The objectives of this proposal involve the x-ray crystallographic structure determination of electron transfer and membrane-interacting proteins. Proteins to be studied include several species of high-spin cytochrome c', Chromatium flavocytochrome c552, Ch1. thiosulfatophilum cytochrome c555, and C. adamauteus phosphilipase A2. Aims of the work involve extending our knowledge of structural/function relationships in heme proteins and membrane and degrading enzymes; specifically these include: a) the nature of redox-linked conformational changes, b) mechanisms for redox potential regulation, and c) origins of reactive specificity in both electron transfer and protein-membrane interactions. Additional objectives relate to studying how amino acid sequence variations are accommodated in recurring protein structural motifs, and the use of high resolution structural data to study protein dynamical effects.