Reduction kinetics of bacterial cytochromes c2

Abstract

In a continuing effort to understand the mechanism of electron transfer by c-type cytochromes we have extended our investigations of the oxidation and reduction of Rhodospirillum rubrum cytochrome c 2. We have utilized the oxidant, oxidized azurin, and the reductants SO 2 −, S 2O 4 2−, sodium ascorbate, and reduced azurin. The results of these studies demonstrate that, as found previously with the iron hexacyanides, electron transfer apparently takes place at the exposed heme edge. Furthermore, we report studies on the reduction of ferricytochrome c 2 from Rhodopseudomonas sphaeroides, Rhodopseudomonas capsulata, Rhodomicrobium vannielii, and Rhodopseudomonas palustris by potassium ferrocyanide. Based on the amino acid sequence homology between the various cytochromes c 2 and presumed structural homology, the observed rates of electron transport are analyzed in terms of the structure in the region of the exposed heme edge.