No abstract

1H-n.m.r. studies of horse, tuna, Candida krusei and Saccharomyces cerevisiae cytochromes c showed that each of the proteins contains a similar cluster of residues at the bottom of the protein that assists in shielding the haem from the solvent. The relative positions of the residues forming these clusters vary continuously with temperature, and they change with the change in protein redox state. This conformational heterogeneity is discussed with reference to the conformational flexibility of cytochrome c around residues 57, 59 and 74. Spectroscopic measurements of pKa values for Lys-55 (horse and tuna cytochromes c) and His-33 and His-39 (C. krusei and S. cerevisiae cytochromes c) are in excellent agreement with expectations based on chemical-modification studies of horse cytochrome c. [Bosshard & Zürrer (1980) J. Biol. Chem. 255, 6694-6699] and on the X-ray-crystallographic structure of tuna cytochrome c [Takano & Dickerson (1981) J. Mol. Biol. 153, 79-94, 95-115].

A review of the literature concerning the structure and electron-transfer function of cytochrome c is presented. Emphasis is placed upon the conformational heterogeneity of cytochrome c, particularly of the region around the exposed edge of the haem that is the reductase and oxidase interaction region, and upon the variation in sequence of eukaryotic cytochromes c.

The relevance of this finding to the electron‐transfer function of cytochrome c is discussed.