KINETICS AND MECHANISM OF THE REDUCTION OF HORSE HEART FERRICYTOCHROME-C BY GLUTATHIONE

A detailed investigation of the reduction of cytochrome c by glutathione has shown that the reaction proceeds through several steps. A rapid combination of the reducing agent with the cytochrome leads to the formation of a glutathione-cytochrome intermediate in which the glutathione most likely interacts with the edge of the heme moiety. The electron transfer takes place in a subsequent slower step. Since cytochrome c(III) exists in two conformational forms at neutral pH [Kujundzic, N., & Everse, J. (1978) Biochem. Biophys. Res. Commun. 82, 1211], the reduction of cytochrome c by glutathione may be represented by [Formulae ommited] At 25 °C, pH 7.5 and an ionic strength of 1.0 (NaCl), k1 = 1.2 × 10-3 s-1, k2 = 2.0 × 10-3 s-1 k1 = 2.9 × 103 M-1 and K2 = 5.3 × 103 M-1. The reaction is catalyzed by trisulfides and second-order rate constants of 4.55 × 103 and 7.14 × 103 s-1 were obtained for methyl trisulfide and cysteine trisulfide, respectively. © 1979, American Chemical Society. All rights reserved.