An hypothetical structure for an intermolecular electron transfer complex of cytochromes c and b5.

Abstract An hypothetical structural complex of cytochromes c and b5 which optimizes intermolecular complementary charge and steric interactions was generated by a least-squares fitting process. The interactions formed in this complex constrain the two heme prosthetic groups to be nearly coplanar at a closest approach distance for resonant heterocyclic porphyrin ring atoms of 8.4 A. The structural properties of the complex are discussed in the general context of oxidoreduction processes carried out by reversibly bound protein electron carriers.