Crystallographic and Mechanistic Studies of Cytochrome c Peroxidase

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9420845 Kraut The electron transfer reaction between cytochrome c peroxidase (CcP) and cytochrome c will be examined. CcP is a 34,000 M.W. monomeric heme enzyme that catalyses the reduction of peroxide to water, using cytochrome c as the electron donor. One step in the catalytic cycle of CcP involves rapid electron transfer between the hemes of CcP and cytochrome c, although the heme edges are separated by at least 17 . The crystal structure of CcP and the complex formed between CcP and cytochrome c have been determined in this laboratory. These crystal structures will be used to guide site-directed mutagenesis experiments aimed at perturbing specific elements of the electron transfer pathway between the two hemes. The effect of specific mutations on structure and electron transfer rates will be evaluated using crystallography and transient spectroscopy techniques. The results will help to define the structural elements that are required for the long distance electron transfer reaction between the hemes of CcP and cytochrome c. %%% All aerobic organisms obtain the energy required for biosynthetic reactions from the conversion of oxygen to water. This is accomplished by a highly ordered enzyme system that transfers electrons from metabolites to oxygen, while preserving some of the energy from this reaction for use in synthetic reactions. The cellular electron transfer system consists of a variety of metal centers that are embedded in proteins. It is clear that the electrons are transferred between the metal centers, and the electron transfer is controlled by the protein surrounding the metal centers, but little is known about how the protein matrix makes these electron transfer reactions efficient and highly specific. As a first step in understanding this process, this investigation will examine how electron transfer is conducted rapidly between the metal centers of twm well-defined protein molecules. The larger goal of the work is to understand how aerobic organisms achieve the efficient and specific electron transfer reactions that are required for survival. ***