Enzymatic process for the manufacture of ascorbic acid 2-keto-L-gulonic acid and esters of 2-keto-L-gulonic acid

Abstract

The present invention is directed toward efficient, high-yield processes for making ascorbic acid, 2-keto-L-gulonic acid, and esters of 2-keto-L-gulonic acid. The processes comprise reacting the appropriate starting materials with a hydrolase enzyme catalyst such as a protease, an esterase, a lipase or an amidase.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/017,879, filed on May 17, 1996.

FIELD OF THE INVENTION

This invention relates to processes for the manufacture of ascorbic acid, 2-keto-L-gulonic acid (KLG), and esters of KLG. More particularly, the present invention relates to the use of enzyme catalysts in the manufacture of ascorbic acid, KLG or esters of KLG.

BACKGROUND OF THE INVENTION

Ascorbic acid, also known as vitamin C, is a dietary factor which must be present in the human diet to prevent scurvy and which has been identified as an agent that increases resistance to infection. Ascorbic acid is used commercially, for example, as a nutrition supplement, color fixing agent, flavoring and preservative in meats and other foods, oxidant in bread doughs, abscission of citrus fruit in harvesting and reducing agent in analytical chemistry.

One current method for the manufacture of ascorbic acid utilizes a modification of the original Reichstein-Grossner synthesis (Reichstein et al., Helv. Chim. Acta, 17:311 (1934); U.S. Pat. No. 2,301,811 to Reichstein; all references cited herein are specifically incorporated by reference). In this process a glucose source is converted to ascorbic acid. During conversion an intermediate of a diacetonide of KLG is produced.

Several two stage methods exists for the manufacture of ascorbic acid. In the first stage, glucose is converted via fermentation processes to either an isolated intermediate of KLG (Sonoyama et al., Applied and Envtl. Microbiology, 43:1064-1069 (1982); Anderson et al., Science, 230:144-149 (1985); Shinjoh et al., Applied and Envtl. Microbiology, 61:413-420 (1995)) or the intermediate of the Reichstein-Grossner synthesis, the diacetonide of KLG.

The second stage, which converts either of the intermediates to ascorbic acid, proceeds by one of two reported routes. The first route, a modification of the latter steps of the Reichstein-Grossner synthesis, requires a multitude of steps whereby the intermediate is esterified with methanol under strongly acidic conditions to produce methyl-2-keto-L-gulonate (MeKLG). The MeKLG is then reacted with base to produce a metal ascorbate salt. Finally, the metal ascorbate salt is treated with an acidulant to obtain ascorbic acid. The second route is a one-step method comprising acid-catalyzed cyclization of KLG, as originally disclosed in GB Patent No. 466548 to Reichstein) and later modified by Yamazaki (Yamazaki, J. Agri. Chem. Soc. Japan, 28:890-894 (1954), and Chem. Abs., 50:5992d) and again by Yodice (WO 87/00839). The Yodice method is commercially undesirable because it uses large amounts of gaseous hydrogen chloride, requires very expensive process equipment and produces an ascorbic acid product requiring extensive purification.

Lipases, a group of hydrolase enzymes, have been used with some success in the synthesis of esters of organic acids. In particular, lipases have been utilized in the transesterification of alcohols in which the esterifying agent is irreversible, such as when vinyl acetate is used as the esterifying agent (Thiel, Catalysis Today, 517-536 (1994)). Gutman et. al., Tetrahedron Lett., 28:3861-3864 (1987), describes a process for preparing simple 5-membered ring lactones from gamma-hydroxy methyl esters using porcine pancreatic lipase as the catalyst. However, Gutman et al., Tetrahedron Lett., 28:5367-5368 (1987), later reported that substituting delta-hydroxy methyl esters for gamma-hydroxy methyl esters and using the same catalyst produced only polymers. In EP 0 515 694 A1 to Sakashita et. al., a synthesis of esters of ascorbic acid, which are acylated on the primary hydroxyl group, comprises reacting ascorbic acid with a variety of fatty acid active esters (i.e., fatty acid vinyl esters) in a polar organic solvent in the presence of a lipase.

Thus, there exists a need in the art for methods of producing (a) ascorbic acid or metal salts thereof from KLG or esters of KLG, (b) KLG from esters of KLG and (c) esters of KLG from KLG, which have high yield and high purity with little or no by-product formation and are conducted under mild conditions. Accordingly, it is to the provision of such that the present invention is primarily directed.

SUMMARY OF THE INVENTION

The present invention discloses an advancement in the chemical and biological arts in which a process for preparing ascorbic acid comprises contacting KLG or an ester of KLG with a hydrolase enzyme catalyst.

In another embodiment of the present invention, a process for producing KLG comprises contacting an ester of KLG in an aqueous solution with a hydrolase enzyme catalyst.

In still another embodiment of the present invention, a process for producing esters of KLG from KLG comprises contacting an alcoholic solution of KLG with a hydrolase enzyme catalyst. The alcoholic solution contains an alcohol corresponding to an alkyl moiety of the ester of KLG to be prepared.

In still another embodiment of the present invention, a process for producing esters of KLG from esters of KLG comprises contacting an alcoholic solution of a first ester of KLG with a hydrolase enzyme catalyst. The alcoholic solution contains an alcohol corresponding to an alkyl moiety of a second ester of KLG which is to be prepared.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to the unexpected discovery that ascorbic acid can be formed from KLG or, more preferably, esters of KLG by inducing ring closure of KLG or esters of KLG using a hydrolase enzyme as a catalyst. The process for producing the ascorbic acid may be performed in the melt or in solution. The process may also be performed in vivo or in vitro. For in vivo processes, the hydrolase enzyme catalyst may be naturally occurring within a host cell or may be introduced into a host cell or organism by recombinant DNA methods.

The present invention is also directed to the unexpected discovery that KLG can be prepared in a reversible reaction by reacting an ester of KLG in an aqueous solution using a hydrolase enzyme as a catalyst. Moreover, the present invention is directed to the unexpected discovery that an ester of KLG can be prepared by reacting KLG or another ester of KLG in an alcoholic solution using a hydrolase enzyme as a catalyst. The alcohol used to prepare the solution corresponds to the alkyl moiety of the ester of KLG being prepared.

The hydrolase enzymes for use as catalysts in the processes of the present invention may be derived from or isolated from any appropriate source organisms. Examples of which include, but are not limited to, plants, microorganisms, and animals, such as yeast, bacteria, mold, fungus, birds, reptiles, fish, and mammals. Hydrolase enzymes for the purposes of this invention are defined generally by the enzyme class E.C.3.-.-.-, as defined in Enzyme Nomenclature (Academic Press, 1992), and are commercially available.

Preferred hydrolase enzymes are those capable of effecting hydrolysis of molecules containing carbonyl or phosphate groups. More specifically, the preferred hydrolases are capable of effecting hydrolysis at a carbonyl carbon bearing a heteroatom single bond. Examples of such carbonyl carbons bearing a heteroatom single bond include, but are not limited to, esters, thioesters, amides, acids, acid halides, and the like. The preferred hydrolases include the enzyme class E.C.3.1.-.-, which includes hydrolases acting on ester bonds, such as esterases and lipases; the enzyme class E.C.3.2-.-, which includes glycosidases; the enzyme class E.C.3.4-.-, which includes peptide hydrolases, such as proteases; and the enzyme class E.C.3.5.-.-, which includes amidases acting on bonds other than peptide bonds. Most preferred hydrolases include proteases, amidases, lipases, and esterases.

More preferred hydrolases contain an active site serine residue which is capable of undergoing esterification or transesterification with KLG or esters of KLG. Even more preferred are those hydrolases which contain the catalytic triad of serine, histidine and apartic acid.

Preferred proteases include those derived from bacteria of the genera Bacillus or Aspergillus. Particularly preferred proteases are those obtained from the bacteria Bacillus licheniformis. Preferred proteases are those containing at least 70% sequence homology with Subtilisin. Proteases having sequence homology with Subtilisin are used in the detergent industry and, therefore, are readily available. More preferred are proteases having at least 80% sequence homology with Subtilisin, even more preferred are proteases having at least 90% sequence homology with Subtilisin and, in particular, proteases having at least 95% sequence homology to Subtilisin. A highly preferred protease is Subtilisin itself having an amino acid sequence (SEQ ID NO: 1) described by Smith et al., J. Biol. Chem., 243:2184-2191 (1968), and given below:

__________________________________________________________________________MMRKKSFWLG MLTAFMLVFT MAFSDSASAA QPAKNVEKDYIVGFKSGVKT ASVKKDIIKE SGGKVDKQFR IINAAKAKLDKEALKEVKND PDVAYVEEDH VAKALAQTVP YGIPLIKADKVQAQGFKGAN VKVAVLDTGI QASHPDLNVV GGASFVAGEAYNTDGNGHGT HVAGTVAALD NTTGVLGVAP SVSLYAVKVLNSSGSGTYSG IVSGIEWATT NGMDVINMSL GGPSGSTAMKQAVDNAYARG VVVVAAAGNS GSSGNTNTIG YPAKYDSVIAVGAYDSNSNR ASFSSVGAEL EVMAPGAGVY STYPTSTYATLNGTSMASPH VAGAAALILS KHPNLSASQV RNRLSSTATYLGSSFYYGKG LINVEAAAQ.__________________________________________________________________________

For the convenience of the reader, Table 1 provides a summary of amino acid shorthand used above and in the remainder of the specification.

TABLE 1______________________________________Amino Acid Three-LetterSymbol Abbreviation One-Letter______________________________________Alanine Ala AArginine Arg RAsparagine Asn NAspartic Acid Asp DCysteine Cys CGlutamine Gln QGlutamic Acid Glu EGlycine Gly GHistidine His HIsoleucine Ile ILeucine Leu LLysine Lys KMethionine Met MPhenylalanine Phe FProline Pro PSerine Ser SThreonine Thr TTryptophan Trp WTyrosine Tyr YValine Val V______________________________________

Also encompassed by the scope of the present invention are proteases corresponding to one to six site-specific mutants, sequence additions, and sequence deletions of the sequence given above. Even more preferred are proteases corresponding to zero to two site-specific mutants of the Subtilisin sequence given above.

Esterases suitable for the present invention include those obtained from pig liver extract. Preferred esterases are those having at least 70% sequence homology with pig liver esterase having an amino acid sequence (SEQ ID NO: 2) described in Matsushima et al., FEBS Lett., 293:37 (1991), and given below:

__________________________________________________________________________MWLLPLVLTS LASSATWAGQ PASPPVVDTA QGRVLGKYVSLEGLAFTQPV AVFLGVPFAK PPLGSLRFAP PQPAEPWSFVKNTTSYPPMC CQDPVVEQMT SDLFTNFTGK ERLTLEFSEDCLYLNIYTPA DLTKRGRLPV MVWIHGGGLV LGGAPMYDGVVLAAHENFTV VVVAIQYRLG IWGFFSTGDE HSRGNWGHLDQVAALHWVQE NIANFGGDPG SVTIFGESFT AGGESVSVLVLSPLAKNLFH RAISESGVAL TVALVRKDMK AAAKQIAVLAGCKTTTSAVF TFVHCLRQKS EDELLDLTLK MKFLTLDFHGDQRESHPFLP TVVDGVLLPK MPEEILAEKD FTFNTVPYIVGINKQEFGWL LPTMMGFPLS EGKLDQKTAT SLLWKSYPIANIPEELTPVA TFTDKYLGGT DDPVKKKDLF LDLMGDVVFGVPSVTVARQH RDAGAPTYMY EFQYRPSFSS DKFTKPKTVIGDHGDEIFSV FGFPLLKGDA PEEEVSLSKT VMKFWANFARSGNPNGEGLP HEPFTMYDQE EGYLQIGVNT QAAKRLKGEEVAFWNDLLSK EAAKKPPKIK HAEL.__________________________________________________________________________

Esterases more preferably have at least 80% sequence homology with the sequence of the pig liver esterase given above, even more preferably at least 90% sequence homology, especially preferred at least 95% sequence homology. Highly preferred is the pig liver esterase having the sequence given above.

Also encompassed by the scope of the present invention are esterases corresponding to one to six site-specific mutants, sequence additions, and sequence deletions of the sequence given above. Even more preferred are esterases corresponding to zero to two site-specific mutants of the pig liver esterase sequence given above.

Preferred lipases include those isolated from pigs and other mammals, microorganisms, and plants. This includes, but is not limited to, lipases obtained from the genera Aspergillus, Mucor, Candida, Pseudomonas, Humicola, Rhizopus, Chromobacterium, Alcaligenes, Geotricum, and Penicillium. Preferred lipases also include extracellular lipases, such as cutinases. More preferred lipases have at least 70% sequence homology with Candida Antartica type B lipase, even more preferred have at least 80% sequence homology, still more preferred have at least 90% sequence homology, and even more preferred have at least 95% sequence homology. A highly preferred lipase is the Candida Antartica type B lipase itself which has an amino acid sequence (SEQ ID NO: 3) described by Uppenberg et al., Structure, 2:293, 453 (1994), and given below:

__________________________________________________________________________MKLLSLTGVA GVLATCVAAT PLVKRLPSGS DPAFSQPKSVLDAGLTCQGA SPSSVSKPIL LVPGTGTTGP QSFDSNWIPLSTQLGYTPCW ISPPPFMLND TQVNTEYMVN AITALYAGSGNNKLPVLTWS QGGLVAQWGL TFFPSIRSKV DRLMAFAPDYKGTVLAGPLD ALAVSAPSVW QQTTGSALTT ALRNAGGLTQIVPTTNLYSA TDEIVQPQVS NSPLDSSYLF NGKNVQAQAVCGPLFVIDHA GSLTSQFSYV VGRSALRSTT GQARSADYGITDCNPLPAND LTPEQKVAAA ALLAPAAAAI VAGPKQNCEPDLMPYARPFA VGKRTCSGIV TP.__________________________________________________________________________

Also encompassed by the scope of the present invention are lipases corresponding to one to six site-specific mutants, sequence additions, and sequence deletions of the sequence given above. Even more preferred are lipases corresponding to zero to two site-specific mutants of the Candida Antartica type B sequence given above.

Preferred amidases include those isolated from bacteria of the genus Penicillium. A more preferred amidase has at least 80% sequence homology with Penicillin acylase. A particularly preferred amidase is Penicillin acylase, which is also referred to as Penicillin amidohydrolase, E.C. 3.5.1.11 (Duggleby et al., Nature, 373:264-268 (1995)).

For hydrolases containing serine at their active site, the first step in the reaction of either KLG or esters of KLG is believed to involve formation of a KLG-enzyme ester via acylation by KLG of the active site serine. Intra-molecular ring closure is believed to yield ascorbic acid (or its salts), whereas alcoholysis yields an ester of KLG and hydrolysis yields KLG.

The process of the present invention comprises contacting either KLG or an ester of KLG with a hydrolase enzyme to form ascorbic acid. Preferably, this reaction is performed in the presence of an organic solvent system, an aqueous solvent system or a mixture thereof. The organic solvent is preferably a C.sub.1 -C.sub.6 alcohol. The aqueous solvent system or mixed aqueous and organic solvent systems are more preferable because ascorbic acid, KLG, and esters of KLG are generally more soluble in aqueous solvent systems. For the in vitro production of ascorbic acid from esters of KLG, the mixed aqueous and organic solvent systems or organic solvent systems are preferable to minimize competing hydrolysis reactions which can produce KLG as a byproduct. Aqueous solvent systems are especially preferable when utilizing whole cell systems for the production of ascorbic acid in vivo.

In one aspect of the present invention, the ascorbic acid is produced from KLG or esters of KLG in in vivo, whole cell, and whole organism production systems in the presence of the hydrolase enzyme catalyst. In one embodiment, the hydrolase enzyme is naturally produced by the host organism. In another embodiment, the hydrolase enzyme is produced by the host organism through recombinant DNA technology. For example, a gene sequence encoding a hydrolase enzyme is inserted in a host organism wherein the host organism may be a microorganism, plant, or animal which is capable of expressing the hydrolase enzyme. The host organism producing the hydrolase enzyme is cultured, i.e. provided with nutrients and a suitable environment for growth, in the presence of KLG or esters of KLG to produce the ascorbic acid. Preferably, the host organism is Pantoea citrea, previously referred to as Erwinia herbicola as disclosed in U.S. Pat. No. 5,008,193 to Anderson et al.

Also preferably, the host organism is one that produces KLG in addition to producing the hydrolase enzyme. Representative organisms are from the genera Pantoea or Gluconobacter, such as disclosed in Shinjoh et al.,Applied and Envtl. Microbiology, 61:413-420 (1995), and the genus Corynebacterium as disclosed in Sonoyama et al., Applied and Envtl. Microbiology, 43:1064-1069 (1982).

As used herein, recombinant DNA technology includes in vitro recombinant DNA techniques, synthetic techniques and in vivo recombinant/genetic recombination and is well known in the art. See, for example, the techniques described in Maniatis et al., Molecular Cloning A Laboratory Manual, Cold Spring Harbor Laboratory, N.Y. (1989); Ausubel et al., Current Protocols in Molecular Biology, Greene Publishing Assoc. and Wiley Interscience, N.Y. (1989); Anderson et al., Science, 230:144-149 (1985); and U.S. Pat. No. 5,441,882 to Estell et. al.

For preparations of KLG from esters of KLG, an aqueous solution of the ester of KLG is reacted with the hydrolase enzyme. A co-solvent may be used in the preparation of KLG and is preferably a C.sub.1 -C.sub.6 alcohol.

For preparations of the esters of KLG from KLG or from other esters of KLG, the starting material is in an alcoholic solution wherein the alcohol corresponds to the alkyl moiety of the ester of KLG to be prepared. The alkyl moiety R of the alcohol ROH from which the preferred ester of KLG is derived may be chosen from branched or straight chain, saturated or unsaturated, alkyl, arylalkyls, aryls, and substituted aryls. Preferred R groups include C.sub.1 to C.sub.6 straight or branched chain, saturated or unsaturated alkyls. Even more preferred esters of KLG that are derived for alkyl moieties include MeKLG, ethyl-KLG, n-propyl-KLG, isopropyl-KLG, n-butyl-KLG, isobutyl-KLG, t-butyl-KLG, and n-pentyl-KLG. The most preferred esters of KLG produced are MeKLG due to its ease of manufacture and butyl-KLG due to the advantageous use of the butanol water azeotroph in water removal. A co-solvent may be used in the preparation of the esters of KLG and is preferably water, a C.sub.1 -C.sub.6 alcohol or a mixture thereof.

Preferred temperatures for conducting the reactions of the present invention are from about 5.degree. C. to about 120.degree. C. Even more preferred temperatures are from about 25.degree. C. to about 100.degree. C., and especially preferred temperatures are from about 38.degree. C. to about 80.degree. C.

The preferred pH for the process of the present invention is between about 1.5 and about 10, and a more preferred pH is between about 3 and about 10. For the preparation of ascorbic acid salts from esters of KLG, a particularly preferred pH range is between about 6 and about 10. For the preparation of ascorbic acid as the free acid, a preferred pH is that under the pKa of ascorbic acid and, more preferred, is that under about 4.2. For the preparation of KLG from esters of KLG, a particularly preferred pH range is between about 5 and about 10 due to the generally enhanced rates of enzyme assisted hydrolysis in this pH range. Alternatively, a pH of between about 1.5 and about 2.5 is particularly desirable for the generation of KLG in protonated form. Finally, for the preparation of esters of KLG from KLG, a particularly preferred pH range is between about 3 and about 6.

Each hydrolase has a temperature optimum, a pH optimum, and a pH and temperature range associated with activity. Thus, the appropriate pH and temperature range for a given hydrolase is that which allows for activity of the hydrolase and avoids conditions which are denaturing or inactivating to the hydrolase. For conditions which may be denaturing, such as high temperature or the use of denaturing solvents such as methanol or the like, a minimal amount of testing may be required to define those hydrolases which remain active under a given set of conditions.

The following examples are offered by way of illustration and are not intended to limit the scope of the claimed invention.

EXAMPLES

Proton and carbon nuclear magnetic resonance (NMR) spectra were recorded on a Varian Gemini 300 NMR instrument operating at 300 MHZ in proton mode and 75 MHZ in carbon mode. All NMR spectra were referenced to tetramethylsilane (TMS) at 0 parts per million (ppm) and peak frequencies were recorded in ppm unless otherwise specified. HPLC (high-performance liquid chromatography) analysis was carried out using ultraviolet (UV) detection. Mass spectra (MS) were obtained using a Fisons VG Analytical Ltd. Autospec Mass Spectrometer in FD (field desorption) mode.

The KLG used in the experiments was obtained by fermentation according to the method of Lazarus et. al., Anderson et al., Science, 230:144-149 (1985), and was purified by concentration and crystallization. KLG may alternatively be prepared by chemical conversion from L-sorbose according to methods well known in the art (see e.g., U.S. Pat. No. 2,301,811 to Reichstein). A standard of methyl-2-keto-L-gulonate was purchased from Aldrich Chemical Company (Rare and Specialty Chemicals Catalog), in addition to being prepared by esterification of KLG by methods similar to the procedure used for the preparation of butyl-KLG, described below.

Enzyme hydrolase samples were obtained from commercial sources, including Sigma Chemical Company, Altus Biologics, Recombinant Biocatalysis, Boehringer Mannheim, Novo Nordisk, Genencor International, Thermogen, and Fluka.

Example 1

This example describes the preparation and purification of butyl 2-keto-L-gulonate.

KLG hydrate (51.62 g) was charged in a 500 ml reaction vessel under argon. The reactor was equipped with a 12" vigreux column attached to a Dean Stark trap. The reactor was then charged with n-butanol (310 g) and p-toluene sulfonic acid (2.3 g). The reaction mixture was brought to reflux (81.degree.-82.degree. C.) under mild vacuum (approximately 150 mm Hg) with stirring. Reflux was maintained for a total of two hours and 40 minutes. Heating was discontinued. The reaction was allowed to cool and remain at room temperature for approximately 3 days. The resulting crystals were filtered through a coarse fritted glass filter and washed with two portions of n-butyl alcohol (139 g followed by 37 g). The resulting solids (24.4 g) were dissolved in hot ethyl acetate (250 ml) and recrystallized by standing overnight at room temperature. The recrystallized butyl-KLG was isolated by filtration and dried under vacuum (1.5 mm Hg) until constant weight (15.97 g) was achieved.

The butyl-KLG thus prepared was found to have a solubility of at least 50 weight percent in water as it was soluble at all concentrations under 50 weight percent in water. The recrystallized butyl-KLG of this example had satisfactory proton and carbon NMR spectra and gave the predicted molecular weight by field desorption mass spectrometry.

.sup.1 H NMR (DMSO, digital resolution=0.11 Hz, TMS at half height=0.5 Hz): 6.49 (OH, d, J=1.4 Hz), 4.96 (OH, d, J=5.0 Hz), 4.84 (OH, d, J=4.8 Hz), 4.78 (OH, d, J=7.4 Hz), 4.17-4.0 (m, 2H), 3.5-3.2 (m, approximately 5H), 1.64-1.5 (m, 2H), 1.4-1.35 (m, 2H), 0.89 (CH.sub.3 t, J=7.3).

.sup.13 C NMR (DMSO, decoupled): 169.4, 96.3, 73.8, 72.8, 69.8, 64.5, 62.8, 30.0, 18.4, 13.5.

FDMS: M=250

Example 2

The following procedure was used to demonstrate enzymes for activity under specific pH and aqueous solvent composition conditions.

Initial enzyme screens were carried out as follows. Enzyme (typically 10 mg), aqueous buffer (typically 860 microliters (ul) or 550 ul), aqueous 0.2M CaCl.sub.2 (10 ul), methanol (typically 90 ul or 400 ul), and an aqueous solution of substrate (typically 90 ul of butyl-KLG at a typical concentration of 110,000 ppm) were added to a 2 ml polypropylene centrifuge tube. The resulting solution was vortexed briefly and placed on a shaker bath at 300 rpm at 38.degree. C. (typically for 18 hours or more). After incubation, samples were centrifuged at 14,000 G's (14,000 times gravity) for 20 minutes to remove enzyme, sampled (300 ul), and diluted to one milliliter with distilled water. If not analyzed by HPLC within the day, samples were frozen prior to analysis.

Summarized below in Table 2 is the HPLC data of the products (and remaining substrate) upon reaction of butyl-KLG (BuKLG) with a variety of enzyme hydrolases in water/methanol solution. The data were reported in terms of parts per million of KLG, MeKLG, ascorbic acid (ASA) and butyl-KLG. The reporting of a 0 (zero) indicated that the amount of material present was below the detection threshold of the instrument. Samples labeled as "no enzyme" were controls within a given run. The controls contained substrate but no enzyme and thus represented experimental and HPLC background data.

TABLE 2______________________________________Enzyme Screen forHydrolysis/Methanolysis of Butyl-KLG(38.degree. C. for 41 Hours/38% Methanol-Water/0.1 MES Buffer) Measured, BuKLGEnzyme pH KLG MeKLG ASA (ppm)______________________________________ESL-001-01 5.8 1180 2352 766 4603ESL-001-02 5.6 704 1084 302 7736ESL-001-03 5.7 386 527 257 8931ESL-001-04 5.8 550 752 833 6229ESL-001-05 5.9 456 684 469 7942ESL-001-06 5.6 547 661 129 8896ESL-001-07 5.7 311 755 489 6540No Enzyme 108 325 33 10177No Enzyme (repeat) 107 303 0 9459No Enzyme 117 327 42 9878No Enzyme (repeat) 103 269 2 8593No Enzyme 116 322 0 9473______________________________________

Table 2 illustrates that the hydrolases provided by Recombinant Biocatalysis (ESL-001-01 through ESL-001-07) showed appreciable conversion of butyl-KLG to ascorbic acid, MeKLG, and KLG in a 38% methanol-water solution buffered with morpholinoethane sulfonic acid (MES) hemisodium salt at a pH controlled between 5.5 and 6. These hydrolase enzymes are sold commercially by Recombinant Biocatalysis as recombinant esterases and lipases from thermophilic organisms under the tradename CloneZyme.TM..

Example 3

Table 3 below illustrates that a variety of acylases, esterases, lipases, and proteases showed appreciable conversion of butyl-KLG to ascorbic acid, MeKLG, and KLG in a 38% methanol-water solution buffered at pH 4.8 to 5.8 with MES buffer. The enzymes labeled as ChiroClec.TM. are crystalline crosslinked enzymes sold commercially by Altus Biologics. ChiroClec.TM. -CR is a lipase from Candida rugosa, ChiroClec.TM. -BL is a crystalline form of Subtilisin (a protease), and ChiroClec.TM. -PC is a lipase from Pseudomonas cepacia. Candida Antartica B (a lipase), pig liver esterase (a hydrolase), and Bacillus Species protease showed particularly high levels of activity.

TABLE 3______________________________________Enzyme Screen for Hydrolysis/Methanolysis of Butyl-KLG(38.degree. C. for 16 Hours/38% Methanol-Water/0.1M MES Buffer) Mea- sured BuKLGEnzyme pH KLG MeKLG ASA (ppm)______________________________________Pig Liver Esterase 5.3 446 4377 294 5711Pseudomonas cepacia Lipase 5.3 98 295 65 11355Porcine Pancreatic Lipase 5.4 81 316 49 10709Candida Rugosa Lipase 5.7 122 197 180 10689Alpha-Chymotrypsin 4.9 57 152 20 11174Penicillin Acylase 5.6 83 1307 15 12007Aspergillus niger Lipase 5.7 302 541 55 12290no enzyme 5.1 88 210 5 10393no enzyme 5.1 87 199 1 11553Candida Antartica `A` Lipase 5.4 88 242 37 10670Candida lipolytica Lipase 5.3 91 92 5 11604Candida antartica `B` Lipase 4.8 2915 6807 0 0Humicola lanuginosa Lipase 5 63 90 6 10191Bacillus Species Protease 4.8 2587 5386 9 1251no enzyme 5.2 94 194 1 11552ChiroCLEC-CR (Dry) 5.1 113 222 2 10988ChiroCLEC-BL (Dry) 5.4 194 642 3 5123ChiroCLEC-PC (Pseudomonas 5.7 147 566 1 10471cepacia)Rhizoipus Delmar Lipase 5.5 51 99 1 7392Rhizopus Niveus Lipase 5.1 80 252 17 10453Rhizopus Oryzae Lipase 5.5 58 172 5 10873Chromobacterium Viscosum 5.5 433 187 1 10843LipaseGeotricum Candidum Lipase 5 33 407 7 10000Mucor Javanicus Lipase 5.5 33 167 97 9950Aspergillus Oryzae Protease 5.8 289 781 96 7429Amano-Lipase 5.3 56 300 49 9143PS30 (Pseudomonas)Amano-Lipase AK 5.6 74 167 93 11372(Pseudomonas)______________________________________

Example 4

Table 4 below illustrates that a variety of acylases, esterases, lipases, and proteases showed appreciable conversion of butyl-KLG to ascorbic acid, MeKLG, and KLG in a 38% methanol-water solution buffered at pH 5 to 5.8 with MES buffer. Pig liver esterase, Subtilisin Carlsberg (a protease), Bacillus species protease, ChiroClec.TM. -BL, and Candida Antartica B lipase all show particularly high levels of activity.

TABLE 4______________________________________Enzyme Screen for Hydrolysis/Methanolysis of Butyl-KLG(38.degree. C. for 47.5 Hours/38% Methanol-Water/0.1MMES Buffer) Mea- sured BuKLGEnzyme pH KLG MeKLG ASA (ppm)______________________________________Pig Liver Esterase 5.3 705 2720 246 1368Pseudomonas cepacia Lipase 5.5 77 288 46 6222Porcine Pancreatic Lipase 5.4 229 613 222 10899Candida rugosa Lipase 5.8 104 205 155 5417Alpha-Chymotrypsin 5.1 82 248 54 6092Penicillin Acylase 5.8 100 1607 30 6192Aspergillus niger Lipase 5.3 214 391 29 6470Mucor meihei Lipase 5.6 54 189 108 7041ChiroCLEC-CR 5.5 115 218 99 3769Subtilisin Carlsberg 5.1 3072 47 0 0Candida antarctica A 5.4 166 316 35 5943Candida lipolytica Lipase 5.7 150 166 0 6445Candida antartica B 5.3 2210 3520 60 0Humicola lanuginosa Lipase 5.2 129 241 42 8017Bacillus Sp Protease 5.3 3722 1940 29 38ChiroCLEC-BL protease 5 3744 1724 54 634ChiroCLEC PC lipase 5.7 108 196 5 4148Candida Rugosa esterase 5.6 70 309 61 6734L-1 (Pseudomonas sp)) 5.4 90 336 11 7066L-2 (Candida antartica B) 5.5 2622 3764 14 913L-3 (Candida cylindracea) 5.7 88 158 37 10343L-5 (Candida antartica A) 5.5 153 665 42 4626L-6 (Pseudomonas sp) 5.7 0 379 13 6183L-7 (Porcine pancreas) 5.8 94 884 120 5488L-8 (Humicola sp) 5.5 98 219 7 7299no enzyme 5.6 75 234 5 5508no enzyme 5.5 68 209 6 4968no enzyme 5.6 65 277 16 5320______________________________________

Example 5

Table 5 below illustrates that a variety of lipases and proteases showed appreciable conversion of butyl-KLG to ascorbic acid, MeKLG, and KLG in a 38% methanol-water solution buffered at pH 5.7 to 6.1 with MES buffer. On comparison with the other enzymes in this table, Prozyme 6 (a protease from Aspergillus oryzae), Protease 2A (from Aspergillus oryzae), and GC899 (a commercial detergent protease from Genencor International) showed higher levels of activity.

TABLE 5__________________________________________________________________________Enzyme Screen for Hydrolysis/Methanolysis of Butyl-KLG(38.degree. C. for 19 Hours/38% Methanol-Water/0.1 M MES Buffer)Enzyme Comment Measured pH KLG MeKLG ASA BuKLG (ppm)__________________________________________________________________________PS30 (Pseudomonas) Lipase 5.9 83 213 32 10424GC4 (Geotricum candidum) Lipase 5.7 0 166 0 7475AK (Pseudomonas) Lipase 6 27 205 26 9815G (Penicillium) Lipase 5.8 0 0 0 9441Newlase A (Aspergillus) Protease 5.9 83 299 6 10368Protease M (Aspergillus) Protease 6 498 1054 281 6990Prozyme 6 (Aspergillus) Protease 6 1489 2259 0 4965MAP10 (Mucor) Lipase 6.1 21 148 145 8968No enzyme 5.9 71 169 22 9463No enzyme 5.9 75 191 6 9391No enzyme 5.9 79 196 7 9539D (Rhizopus) Lipase 5.7 44 156 3 8562Newlase II (Rhizopus) Protease 5.9 36 164 12 9586AY30 (Candida) Lipase 6 0 192 33 8725L-10 (Candida) Lipase 5.7 0 0 0 9608CES (Pseudomonas) Lipase 5.8 52 296 42 9491N (Rhizopus) Lipase 5.8 78 404 27 98342A (Protease, Aspergillus) Protease 6.1 937 1158 215 8951Hog Pancreatic Lipase Fluka 6 58 529 130 11114Lipase (Sigma-1754) Lipase 5.8 57 98 47 9845Lipase (Sigma-1754) Lipase 5.8 46 88 82 9428Lipase (Sigma-8525) Lipase 5.9 178 222 60 9041Lipase (Sigma-1754) Lipase 5.7 76 145 89 14257Lipase (Sigma-3126) Lipase 5.9 90 415 130 12756F-15 (Rhizopus) Lipase 5.8 55 165 14 10262Lipozyme (Novo-Liquid) Lipase 6 82 122 160 9100GC899 (protease) Protease 5.8 791 2735 312 11607__________________________________________________________________________

Example 6

Table 6 below illustrates that a variety of lipases and proteases showed appreciable conversion of butyl-KLG to ascorbic acid, MeKLG, and KLG in a 8.6% methanol-water solution buffered at a pH of 5.3 to 6 with MES buffer. Protease M (Aspergillus oryzae), Prozyme 6 (a protease from Aspergillus oryzae), Protease N (Subtilisin), and Protease 2A Aspergillus oryzae), all showed particularly high levels of activity.

TABLE 6__________________________________________________________________________Enzyme Screen for Hydrolysis/Methanolysis of Butyl-KLG(38.degree. for 19 Hours/8.6% Methanol-Water/0.1 M MES)Enzyme Comment Measured pH KLG MeKLG ASA BuKLG (ppm)__________________________________________________________________________PS30 (Pseudomonas) Lipase 5.9 341 163 157 8363GC4 (Geotricum candidum) Lipase 5.9 424 0 8 4192AK (Pseudomonas) Lipase 6 295 432 125 8255G (Penicillium) Lipase 5.8 253 323 0 7678Newlase A (Aspergillus) Protease 5.7 692 302 126 13408R-10 (Penicillium) Lipase 6 527 208 583 5570Protease M (Aspergillus) Protease 6 3650 2262 328 1696Prozyme 6 (Aspergillus) Protease 5.3 7207 694 0 0MAP10 (Mucor) Lipase 6 369 0 231 8334No enzyme 5.8 378 239 132 8272No enzyme 5.8 380 205 19 8582No enzyme 5.8 382 295 43 8785D (Rhizopus) Lipase 5.9 595 326 76 11656Newlase II (Rhizopus) Protease 5.9 323 212 28 8535AY30 (Candida) Lipase 5.9 330 249 254 10195L-10 (Candida) Lipase 5.8 302 69 55 11057AP12 (Aspergillus) Lipase 6 1448 738 129 7730CES (Pseudomonas) Lipase 5.9 197 252 0 8092N (Rhizopus) Lipase 6 582 348 61 9598N (Protease, Bacillus) Protease 5.7 1572 1289 26 18222A (Protease, Aspergillus) Protease 5.7 5891 616 160 764Hog Pancreatic Lipase Fluka 5.8 890 791 158 5284Lipase (Sigma-1754) Lipase 5.9 283 116 148 6196Lipase (Sigma-1754) Lipase 6 348 189 415 8098Lipase (Sigma-8525) Lipase 6 326 93 15 4112Lipase (Sigma-1754) Lipase 6 300 150 154 8057Lipase (Sigma-3126) Lipase 5.8 787 488 99 8829F-15 (Rhizopus) Lipase 5.9 218 124 0 8682Lipozyme (Novo-Liquid) Lipase 5.8 380 95 101 7251GC899 (protease) Protease 5.6 3354 1765 201 6991__________________________________________________________________________

Example 7

Table 7 below illustrates that a variety of acylases, esterases, lipases, and proteases showed appreciable conversion of butyl-KLG to ascorbic acid, MeKLG, and KLG in a 8.6% methanol-water solution buffered at a pH of approximately 5 to 6 with MES buffer. Candida Antartica B lipase, pig liver esterase, and Bacillus species protease showed particularly high levels of activity.

TABLE 7______________________________________Enzyme Screen for Hydrolysis/Methanolysis of Butyl-KLG(38.degree. C. for 19 Hours/8.6% Methanol-Water/0.1M MES)Enzyme Comment KLG MeKLG ASA BuKLG______________________________________L-1 (Pseudomonas sp)) Lipase 137 116 47 7601L-2 (Candida antartica B) Lipase 5249 1921 0 768L-3 (Candida cylindracea) Lipase 183 64 107 6920L-4 (Pseudomonas sp) Lipase 239 163 88 9957L-5 (Candida antartica A) Lipase 278 344 0 6245L-6 (Pseudomonas sp) Lipase 90 219 15 6613L-7 (Porcine pancreas) Lipase 1007 575 106 5392L-8 (Humicola sp) Lipase 209 70 150 7957no enzyme 168 152 6 8753no enzyme 152 144 3 8233no enzyme 170 137 18 8157ESL-001-01 Recom- 1271 906 375 4635ESL-001-02 binant 883 329 332 5949ESL-001-03 Biocat- 290 123 447 7333ESL-001-04 alysis 511 161 306 6207ESL-001-05 Enzymes 364 124 299 6402ESL-001-06 329 117 118 6934ESL-001-07 0 122 430 15752Pig Liver Esterase 2726 3731 423 10Pseudomonas cepacia 241 109 224 9135LipasePorcine Pancreatic Lipase 333 291 314 7888Candida rugosa Lipase 296 86 451 8697no enzyme 153 116 8 8234Alpha-Chymotrypsin protease 330 1076 65 3855Penicillin Acylase 187 1248 157 8110no enzyme 100 73 3 5296no enzyme 144 113 7 8106Aspergillus niger Lipase 479 72 84 8455Mucor meihei Lipase 229 278 156 8620ChiroCLEC-CR lipase 233 155 11 7569Subtilisin Carlsberg 4463 93 0 4428Candida antarctica A lipase 215 0 175 7573Candida lipolytica Lipase 198 62 92 8445Bacillus Sp Protease 4920 642 13 72ChiroCLEC-BL protease 2860 1233 135 4051ChiroCLEC PC lipase 127 62 2 5653Candida Rugosa esterase 178 120 225 9382______________________________________

Example 8

Table 8 below illustrates that a variety of acylases, esterases, lipases, and proteases showed appreciable conversion of butyl-KLG to ascorbic acid, MeKLG, and KLG in a 8.6% methanol-water solution buffered at a pH of approximately 5.8 to 6.2 with MES buffer. Pig liver esterase, Candida Antartica B lipase, Bacillus species protease, and lightly crosslinked crystalline Subtilisin (ChirClec-BL) showed particularly high levels of activity.

TABLE 8__________________________________________________________________________Enzyme Screen for Hydrolysis/Methanolysis of Butyl-KLG(38.degree. C. for 21 Hours/8.6% Methanol-Water/0.2 M MESEnzyme Comment pH KLG MeKLG ASA BUKLG (ppm)__________________________________________________________________________Pig Liver Esterase 5.8 2373 4167 717 83Pseudomonas cepacia Lipase 5.9 173 169 25 7384Porcine Pancreatic Lipase 5.9 303 320 78 6860Candida rugosa Lipase 5.9 260 112 271 7351Alpha-Chymotrypsin protease 5.9 506 1239 146 4707Penicillin Acylase 6 176 1172 98 5392Aspergillus niger Lipase 5.9 493 259 84 6364Mucor meihei Lipase 5.9 243 283 54 7067no enzyme 5.9 198 173 2 7137no enzyme 5.9 216 153 0 7115no enzyme 5.9 223 154 1 7319Candida Antartica `A` Lipase 5.9 222 142 148 6683Candida lipolytica Lipase 6 721 123 25 6721Candida antartica `B` Lipase 5.9 2708 709 20 28Humicola lanuginosa Lipase 5.9 176 129 10 7215Bacillus Species Protease 5.8 5553 603 0 33ChiroCLEC-CR (Dry) 6.1 229 170 2 7191ChiroCLEC-BL (Dry) 5.9 4293 1282 6 1376ChiroCLEC-PC (P. cepacia-Dry) 6.1 240 268 2 7539Rhizoipus Delmar Lipase 6 178 0 0 7097Rhizopus Niveus Lipase 6.2 178 181 61 7102Rhizopus Oryzae Lipase 6.1 159 119 26 7611Chromobacterium Viscosum Lipase 6 415 181 2 7275Geotricum Candidum Lipase 6.1 146 122 6 6140Mucor Javanicus Lipase 6.2 167 95 141 7422Aspergillus Oryzae Protease 6.1 2193 1462 39 2904Candida Rugosa Esterase 5.8 129 132 17 7164__________________________________________________________________________

Example 9

Table 9 below demonstrates the statistical reproduction of the activity detected for highly active enzymes in the preceding examples. Eight of the enzymes from the previous examples, which were identified as showing particularly high levels of activity, were compared under tight pH control. All of the previously identified enzymes with high levels of activity maintained this high level of activity on reanalysis. The enzymes exhibited appreciable conversion of butyl-KLG to ascorbic acid, MeKLG, and KLG in a 8.6% methanol-water solution buffered at a pH of approximately 5.6 to 6 with 0.2M MES buffer. Candida Antartica B lipase, pig liver esterase, and Bacillus species protease showed particularly high levels of activity within this comparative example. Pig liver esterase showed a selectivity toward transesterification as well as significant conversions to ascorbic acid.

TABLE 9______________________________________Enzyme Screen for Hydrolysis/Methanolysis of Butyl-KLG(38.degree. C. for 19 Hours/8.6% Metanol-Water/0.2M MES Buffer) BuKLGEnzyme Comment pH KLG MeKLG ASA (ppm)______________________________________N Protease Protease 6 700 1166 297 5435Candida Antartica B Lipase 5.8 4347 2207 283 0Pig Liver Esterase Esterase 5.9 1947 4258 650 0Bacillus sp Protease Protease 5.6 5137 745 55 0ChiroClec-BL (Dry) Subtilisin 5.8 3485 1235 215 3045Prozyme-6 Protease 5.8 3405 1518 73 1624Protease M Protease 6 554 668 271 63292A Protease Protease 5.9 1585 1501 153 3954no enzyme 6 135 149 14 8170no enzyme 5.9 136 127 16 8418no enzyme 6 142 133 13 8570______________________________________

Example 10

Table 10 below compares the same enzymes as in Example 9 except at a higher concentration of organic solvent. Candida Antartica B and Bacillus species protease showed particularly high levels of activity in that they exhibited appreciable conversion of butyl-KLG to ascorbic acid, MeKLG, and KLG in a 38% methanol-water solution buffered at a pH of approximately 5.6 to 6.2 with 0.2M MES buffer. Decreased, although still appreciable, activity is observed for pig liver esterase relative to that shown in Example 9.

TABLE 10______________________________________Enzyme Screen for Hydrolysis/Methanolysis of Butyl-KLG(38.degree. C. for 19 Hours/38% Methanol-Water/0.2M MES Buffer) BuKLGEnzyme Comment pH KLG MeKLG ASA (ppm)______________________________________N Protease Protease 5.9 176 1144 126 8153Candida Antartica B Lipase 5.8 1701 5710 213 199Pig Liver Esterase Esterase 6 203 1654 173 7030Bacillus sp Protease Protease 5.6 3104 4032 182 213ChiroClec-BL (Dry) Protease 5.8 1261 1693 102 5572Prozyme-6 Protease 6 350 1268 47 7517Protease M Protease 6.2 141 408 199 94002A Protease Protease 6.1 178 626 90 8666no enzyme 6 69 221 8 9418no enzyme 5.9 61 189 7 8790no enzyme 6 63 203 9 9367______________________________________

Example 11

Table 11 below compares the same enzymes as in Example 9 except at a pH buffered around 5.2. Candida Antartica B and pig liver esterase showed particularly high levels of activity in that they exhibited appreciable conversion of butyl-KLG to MeKLG and KLG in a 8.6% methanol-water solution buffered at a pH of approximately 4.9 to 5.3 with 0.2M pyridine/pyridinium hydrochloride buffer. Decreased, although still appreciable, activity is observed for Bacillus species protease relative to Example 9.

TABLE 11______________________________________Enzyme Screen for Hydrolysis/Methanolysis of BUKLG(38.degree. C. for ca. 19 Hours/8.6% Methanol-Water/0.2M Pyridine/Pyridiniuym Hydrochloride) BuKLGEnzyme Comment pH KLG MeKLG ASA (ppm)______________________________________N Protease Protease 5.2 87 237 47 8320Candida Antartica B Lipase 4.9 3460 3097 53 0Pig Liver Esterase Esterase 5.2 1613 5787 37 390Bacillus sp Protease Protease 5.1 1613 2473 70 3757ChiroClec-BL (Dry) Protease 5.1 987 1360 67 5603Prozyme-6 Protease 5.2 700 840 7 6470Protease M Protease 5.3 187 357 0 83872A Protease Protease 5.2 480 643 0 7523no enzyme 5.3 97 0 153 9750no enzyme 5.2 73 0 80 9547______________________________________

Example 12

Table 12 below compares the same enzymes as in Example 11 except at a higher concentration of organic solvent. Candida Antartica B showed particularly high levels of activity in that it exhibited appreciable conversion of butyl-KLG to MeKLG and KLG in 38% methanol-water solution buffered at a pH of approximately 4.7 to 5.1 with 0.2M pyridine/pyridinium hydrochloride buffer. All of the enzymes showed reduced activity relative to Examples 9 and 11.

TABLE 12______________________________________Enzyme Screen for Hydrolysis/Methanolysis of BuKLG(38.degree. C. for ca. 19 Hours/H 4.9/38% Methanol-Water)Enzyme Comment pH KLG MeKLG ASA BuKLG______________________________________N Protease Protease 4.8 0 0 17 9093Candida Antartica B Lipase 4.7 1953 6470 0 5373Pig Liver Esterase Esterase 4.9 47 197 0 11750Bacillus sp Protease 4.9 333 2113 30 10043ProteaseChiroClec-BL (Dry) Protease 4.9 97 447 7 10950Prozyme-6 Protease 4.9 0 113 3 12730Protease M Protease 5.1 73 203 0 158872A Protease Protease 5 67 150 0 13920no enzyme 4.9 87 13 27 11753______________________________________

Example 13

Table 13 below compares the same enzymes as in Examples 9 and 11 except at a pH buffered around 2.3. All enzymes tested showed reduced activity relative to Examples 9 and 11 for conversion of butyl-KLG to ascorbic acid, MeKLG, and KLG in a 8.6% methanol-water solution buffered at a pH of approximately 2.3-2.7 with 0.2M phosphate buffer.

TABLE 13______________________________________Enzyme Screen for Hydrolysis/Methanolysis of BUKLG(38.degree. C. for 20 Hours/8.6% Methanol-Water/pH 2.3 0.2M PhosphateBuffer)Enzyme Comment pH KLG MeKLG ASA BuKLG______________________________________N Protease Protease 2.4 203 0 3 8980Candida Antartica B Lipase 2.4 397 323 0 8463Pig Liver Esterase Esterase 2.4 417 93 0 9500Bacillus Sp Protease Protease 2.3 347 0 0 10987ChiroClec-BL (Dry) Protease 2.3 387 0 0 10580Prozyme-6 Protease 2.4 440 0 0 12357Protease M Protease 2.6 137 333 0 122372A Protease Protease 2.7 163 347 0 10600No enzyme 2.3 487 0 0 10417No enzyme 2.3 413 0 0 9897No enzyme 2.3 407 0 0 9873______________________________________

Example 14

Table 14 below compares the first 5 enzymes of Examples 9 and 11 at a buffered pH of about 6 in their ability to catalyze the esterification of KLG to methyl KLG (MeKLG) or their ability to catalyze ring closure of KLG to ascorbic acid. Low levels of activity are observed relative to examples 9 and 11.

TABLE 14______________________________________Enzyme Screen for Methanolysis of KLG(38.degree. C. for 19 Hours/8.6% Methanol-Water/0.2M MES Buffer)Enzyme Comment pH KLG MeKLG ASA BuKLG______________________________________N Protease Protease 6 3791 0 0 0Candida Antartica B Lipase 6 4258 0 0 0Pig Liver Esterase Esterase 6 4393 0 0 0Bacillus sp Protease Protease 6 4099 0 0 0ChiroClec-BL (Dry) Subtilisin 6.1 3270 0 0 0no enzyme 6 4340 0 0 0no enzyme 6 3295 0 0 0no enzyme 6 4029 0 0 0______________________________________

Example 15

Table 15 below demonstrates the production of MeKLG from KLG using Candida Antartica B lipase as catalyst in 8.6% aqueous methanol at a pH of 3-3.2. The buffer was chosen as a mixture of KLG and its sodium salt (approximately 1/9). The first three entries include enzyme catalyst and are the same conditions in triplicate. The second three entries also run in triplicate and are the same conditions as the first three entries except that no enzyme was present. The first three entries show significant esterification of KLG to MeKLG in the presence of Candida Antartica B lipase. The second three entries demonstrate that the conversion does not proceed in the absence of Candida Antartica B lipase.

TABLE 15__________________________________________________________________________Enzyme Screen for Esterification of KLG68 Hours at 38.degree. C./8.6% Methanol in AqueousPhase/Buffer = KLG + NaKLGEnzyme Comment pH KLG MeKLG ASA BuKLG__________________________________________________________________________Candida Antartica B 8.6% MeOH + KLG 3.1 9227 460 0 0Candida Antartica B 8.6% MeOH + KLG 3.1 9303 530 0 0Candida Antartica B 8.6% MeOH + KLG 3.2 9213 413 0 0no enzyme 8.6% MeOH + KLG 2.9 9530 0 0 0no enzyme 8.6% MeOH + KLG 2.9 9477 0 0 0no enzyme 8.6% MeOH + KLG 2.9 9600 0 0 0__________________________________________________________________________

Example 16

This is example demonstrates the slow decomposition of ascorbic acid under the conditions of HPLC analysis. HPLC sample standards were prepared by dissolving KLG, MeKLG, ascorbic acid (ASA), and butyl-KLG to the appropriate concentration in water. Samples of these standards were placed in filled and sealed vials, stored at room temperature, and analyzed periodically. The HPLC was calibrated on the area response for standards that were injected onto the HPLC as soon as possible after the preparation of the standards. Table 16 below shows the recorded responses for KLG, MeKLG, ascorbic acid, and butyl-KLG standards of 50, 100, and 500 ppm at time 0 (calibration time), at approximately 6.5 hours, approximately 12 hours after sample preparation.

TABLE 16______________________________________ AmountTime Found(minutes) Amount Prepared KLG MeKLG ASA BuKLG______________________________________0 50 ppm standard 51 51.4 53.4 50.6400 39.9 47.7 28.3 42.7715 52 43 0 38.20 100 ppm standard 102 103 107 101400 94.3 106.8 96.6 100.1715 81.8 90.2 57.2 94.20 500 ppm standard 510 514 534 506400 479 496 487 512715 493 495 473 499______________________________________

The ascorbic acid responses were non-linear over time with respect to the other standards and, particularly, with respect to standards of 100 ppm or less. Given that the treatment for Examples 2-16 included approximately 16 hours or more at 38.degree. C. on a shaker bath prior to HPLC analysis, it follows that the actual level of ascorbic acid formed was greater than reported.

This invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

SEQ ID NO: 1 SEQ ID NO: 2 SEQ ID NO: 3 __________________________________________________________________________SEQUENCE LISTING(1) GENERAL INFORMATION:(iii) NUMBER OF SEQUENCES: 3(2) INFORMATION FOR SEQ ID NO:1:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 379 amino acids(B) TYPE: Amino Acid(D) TOPOLOGY: Linear(ii) MOLECULE TYPE: protein(xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:MetMetArgLysLysSerPheTrpLeuGlyMetLeuThrAlaPheMet151015LeuValPheThrMetAlaPheSerAspSerAlaSerAlaAlaGlnPro202530AlaLysAsnValGluLysAspTyrIleValGlyPheLysSerGlyVal354045LysThrAlaSerValLysLysAspIleIleLysGluSerGlyGlyLys505560ValAspLysGlnPheArgIleIleAsnAlaAlaLysAlaLysLeuAsp65707580LysGluAlaLeuLysGluValLysAsnAspProAspValAlaTyrVal859095GluGluAspHisValAlaHisAlaLeuAlaGlnThrValProTyrGly100105110IleProLeuIleLysAlaAspLysValGlnAlaGlnGlyPheLysGly115120125AlaAsnValLysValAlaValLeuAspThrGlyIleGlnAlaSerHis130135140ProAspLeuAsnValValGlyGlyAlaSerPheValAlaGlyGluAla145150155160TyrAsnThrAspGlyAsnGlyHisGlyThrHisValAlaGlyThrVal165170175AlaAlaLeuAspAsnThrThrGlyValLeuGlyValAlaProSerVal180185190SerLeuTyrAlaValLysValLeuAsnSerSerGlySerGlyThrTyr195200205SerGlyIleValSerGlyIleGluTrpAlaThrThrAsnGlyMetAsp210215220ValIleAsnMetSerLeuGlyGlyProSerGlySerThrAlaMetLys225230235240GlnAlaValAspAsnAlaTyrAlaArgGlyValValValValAlaAla245250255AlaGlyAsnSerGlySerSerGlyAsnThrAsnThrIleGlyTyrPro260265270AlaLysTyrAspSerValIleAlaValGlyAlaValAspSerAsnSer275280285AsnArgAlaSerPheSerSerValGlyAlaGluLeuGluValMetAla290295300ProGlyAlaGlyValTyrSerThrTyrProThrSerThrTyrAlaThr305310315320LeuAsnGlyThrSerMetAlaSerProHisValAlaGlyAlaAlaAla325330335LeuIleLeuSerLysHisProAsnLeuSerAlaSerGlnValArgAsn340345350ArgLeuSerSerThrAlaThrTyrLeuGlySerSerPheTyrTyrGly355360365LysGlyLeuIleAsnValGluAlaAlaAlaGln370375(2) INFORMATION FOR SEQ ID NO:2:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 584 amino acids(B) TYPE: Amino Acid(D) TOPOLOGY: Linear(ii) MOLECULE TYPE: protein(xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:MetTrpLeuLeuProLeuValLeuThrSerLeuAlaSerSerAlaThr151015TrpAlaGlyGlnProAlaSerProProValValAspThrAlaGlnGly202530ArgValLeuGlyLysTyrValSerLeuGluGlyLeuAlaPheThrGln354045ProValAlaValPheLeuGlyValProPheAlaLysProProLeuGly505560SerLeuArgPheAlaProProGlnProAlaGluProTrpSerPheVal65707580LysAsnThrThrSerTyrProProMetCysCysGlnAspProValVal859095GluGlnMetThrSerAspLeuPheThrAsnPheThrGlyLysGluArg100105110LeuThrLeuGluPheSerGluAspCysLeuTyrLeuAsnIleTyrThr115120125ProAlaAspLeuThrLysArgGlyArgLeuProValMetValTrpIle130135140HisGlyGlyGlyLeuValLeuGlyGlyAlaProMetTyrAspGlyVal145150155160ValLeuAlaAlaHisGluAsnPheThrValValValValAlaIleGln165170175TyrArgLeuGlyIleTrpGlyPhePheSerThrGlyAspGluHisSer180185190ArgGlyAsnTrpGlyHisLeuAspGlnValAlaAlaLeuHisTrpVal195200205GlnGluAsnIleAlaAsnPheGlyGlyAspProGlySerValThrIle210215220PheGlyGluSerPheThrAlaGlyGlyGluSerValSerValLeuVal225230235240LeuSerProLeuAlaLysAsnLeuPheHisArgAlaIleSerGluSer245250255GlyValAlaLeuThrValAlaLeuValArgLysAspMetLysAlaAla260265270AlaLysGlnIleAlaValLeuAlaGlyCysLysThrThrThrSerAla275280285ValPheThrPheValHisCysLeuArgGlnLysSerGluAspGluLeu290295300LeuAspLeuThrLeuLysMetLysPheLeuThrLeuAspPheHisGly305310315320AspGlnArgGluSerHisProPheLeuProThrValValAspGlyVal325330335LeuLeuProLysMetProGluGluIleLeuAlaGluLysAspPheThr340345350PheAsnThrValProTyrIleValGlyIleAsnLysGlnGluPheGly355360365TrpLeuLeuProThrMetMetGlyPheProLeuSerGluGlyLysLeu370375380AspGlnLysThrAlaThrSerLeuLeuTrpLysSerTyrProIleAla385390395400AsnIleProGluGluLeuThrProValAlaThrPheThrAspLysTyr405410415LeuGlyGlyThrAspAspProValLysLysLysAspLeuPheLeuAsp420425430LeuMetGlyAspValValPheGlyValProSerValThrValAlaArg435440445GlnHisArgAspAlaGlyAlaProThrTyrMetTyrGluPheGlnTyr450455460ArgProSerPheSerSerAspLysPheThrLysProLysThrValIle465470475480GlyAspHisGlyAspGluIlePheSerValPheGlyPheProLeuLeu485490495LysGlyAspAlaProGluGluGluValSerLeuSerLysThrValMet500505510LysPheTrpAlaAsnPheAlaArgSerGlyAsnProAsnGlyGluGly515520525LeuProHisTrpProPheThrMetTyrAspGlnGluGluGlyTyrLeu530535540GlnIleGlyValAsnThrGlnAlaAlaLysArgLeuLysGlyGluGlu545550555560ValAlaPheTrpAsnAspLeuLeuSerLysGluAlaAlaLysLysPro565570575ProLysIleLysHisAlaGluLeu580(2) INFORMATION FOR SEQ ID NO:3:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 342 amino acids(B) TYPE: Amino Acid(D) TOPOLOGY: Linear(ii) MOLECULE TYPE: protein(xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:MetLysLeuLeuSerLeuThrGlyValAlaGlyValLeuAlaThrCys151015ValAlaAlaThrProLeuValLysArgLeuProSerGlySerAspPro202530AlaPheSerGlnProLysSerValLeuAspAlaGlyLeuThrCysGln354045GlyAlaSerProSerSerValSerLysProIleLeuLeuValProGly505560ThrGlyThrThrGlyProGlnSerPheAspSerAsnTrpIleProLeu65707580SerThrGlnLeuGlyTyrThrProCysTrpIleSerProProProPhe859095MetLeuAsnAspThrGlnValAsnThrGluTyrMetValAsnAlaIle100105110ThrAlaLeuTyrAlaGlySerGlyAsnAsnLysLeuProValLeuThr115120125TrpSerGlnGlyGlyLeuValAlaGlnTrpGlyLeuThrPhePhePro130135140SerIleArgSerLysValAspArgLeuMetAlaPheAlaProAspTyr145150155160LysGlyThrValLeuAlaGlyProLeuAspAlaLeuAlaValSerAla165170175ProSerValTrpGlnGlnThrThrGlySerAlaLeuThrThrAlaLeu180185190ArgAsnAlaGlyGlyLeuThrGlnIleValProThrThrAsnLeuTyr195200205SerAlaThrAspGluIleValGlnProGlnValSerAsnSerProLeu210215220AspSerSerTyrLeuPheAsnGlyLysAsnValGlnAlaGlnAlaVal225230235240CysGlyProLeuPheValIleAspHisAlaGlySerLeuThrSerGln245250255PheSerTyrValValGlyArgSerAlaLeuArgSerThrThrGlyGln260265270AlaArgSerAlaAspTyrGlyIleThrAspCysAsnProLeuProAla275280285AsnAspLeuThrProGluGlnLysValAlaAlaAlaAlaLeuLeuAla290295300ProAlaAlaAlaAlaIleValAlaGlyProLysGlnAsnCysGluPro305310315320AspLeuMetProTyrAlaArgProPheAlaValGlyLysArgThrCys325330335SerGlyIleValThrPro340__________________________________________________________________________

Claims

1. A process for preparing ascorbic acid comprising contacting a compound selected from the group consisting of 2-keto-L-gulonic acid and an ester of 2-keto-L-gulonic acid with a hydrolase enzyme catalyst to form ascorbic acid.

2. The process of claim 1 wherein the hydrolase enzyme catalyst is selected from the group consisting of a protease, an esterase, a lipase and an amidase.

3. The process of claim 2 wherein the protease is obtained from a genera selected from the group consisting of Bacillus or Aspergillus.

4. The process of claim 3 wherein the protease is obtained from a Bacillus licheniformis bacteria.

5. The process of claim 4 wherein the protease is the Subtilisin protease having the sequence as shown in SEQ ID NO: 1.

6. The process of claim 2 wherein the esterase is obtained from pig liver extract.

7. The process of claim 6 wherein the esterase is the pig liver esterase having the sequence as shown in SEQ ID NO: 2.

8. The process of claim 2 wherein the lipase is obtained from a genera selected from the group consisting of Aspergillus, Mucor, Candida, Pseudomonas, Humicola, Rhizopus, Chromobacterium, Alcaligenes, Geotricum and Penicillium.

9. The process of claim 8 wherein the lipase is the Candida Antartica B lipase having the sequence as shown in SEQ ID NO: 3.

10. The process of claim 2 wherein the amidase is obtained from a genus Penicillium.

11. The process of claim 10 wherein the amidase is the Penicillin acylase.

12. The process of claim 1 wherein the hydrolase enzyme catalyst contains an active site serine residue.

13. The process of claim 12 wherein the hydrolase enzyme catalyst contains a catalytic triad of serine, histidine and aspartic acid.

14. The process of claim 1 wherein, prior to contacting the compound with the hydrolase enzyme catalyst, the compound is formed into a solution with a solvent.

15. The process of claim 14 wherein the solvent is selected from the group consisting of water, a C.sub.1 to C.sub.6 alcohol and a mixture thereof.

16. The process of claim 1 wherein contacting the compound with the hydrolase enzyme catalyst occurs at a pH between about 1.5 and 10.

17. The process of claim 1 wherein contacting the compound with the hydrolase enzyme catalyst occurs at a temperature from about 5.degree. C. to about 120.degree. C.

18. The process of claim 1 wherein, prior to contacting the compound with the hydrolase enzyme catalyst, the hydrolase enzyme catalyst is naturally expressed from a host organism in vivo.

19. The process of claim 1 wherein, prior to contacting the compound with the hydrolase enzyme catalyst, a gene sequence encoding the hydrolase enzyme catalyst is inserted into a host organism and the host organism is cultured to express the hydrolase enzyme catalyst in vivo.

20. The process of claim 19 wherein the host organism is Pantoea citrea.

21. The process of claim 18 or claim 19 wherein the host organism produces 2-keto-L-gulonic acid.