The specific nature of the interaction between biological oxidation-reduction proteins is poorly understood. Thus to address this question and the question of the factors mediating protein-protein interactions in general we are investigating the mechanism of electron transfer by c-type cytochromes. Our present focus is in three general areas: 1) the determination of the kinetic mechanism of the oxidation and reduction of mammalian cytochrome c by nonphysiological reactants, 2) the determination of alterations or differences in this mechanism when electron transfer takes place between cytochrome c and other oxidation-reduction proteins, specifically, cytochrome b5 and high potential non-heme iron proteins, and 3) the role of protein motion (dynamics) in the structure and function of cytochromes and, ultimately, proteins in general. It is our ultimate goal to understand in molecular terms the relative contribution of those factors (electrostatics, non-polar interaction, thermodynamics, protein dynamics and coupled conformational changes) mediating protein-protein interactions and to use this information to more fully understand electron-transfer coupled to energy conservation and protein-structure-function relations.