Kinetics and mechanism of the reduction of horse heart ferricytochrome C by glutathione

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Abstract
A detailed investigation of the reduction of cytochrome c by glutathione showed 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 where the glutathione most likely interacts with the edge of the heme moiety. The electron transfer takes place in a subsequent slower step. Cytochrome c(III) exists in 2 conformational forms at neutral pH; the reduction of cytochrome c by glutathione may be represented by .**GRAPHIC**. At 25.degree. C, pH 7.5 and an ionic strength of 1.0 (NaCl), k1 = 1.2 .times. 10-3 s-1, k2 = 2.0 .times. 10-3 s-1, K1 = 2.9 .times. 103 M-1 and K2 = 5.3 .times. 103 M-1. The reaction is catalyzed by trisulfides; 2nd-order rate constants of 4.55 .times. 103 and 7.14 .times. 103 M-1 s-1 were obtained for methyl trisulfide and cysteine trisulfide, respectively.