The cytochrome c3-ferredoxin electron transfer complex: Cross-linking studies

Abstract

The tetrahemic cytochrome c 3 ( M r = 13000) and the ferredoxin I isolated from Desulfovibrio desulfuricans Norway are specific physiological partners in the sulfate-reducing bacteria electron transfer chain. The study of their interaction should improve the understanding of the electron transfer mechanism between heme and iron sulfur clusters. Incubation of cytochrome c 3 and ferredoxin I together with 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide metho- p-toluenesulfonate allows the formation of a covalently cross-linked complex with a stoichiometry of one cytochrome c 3 molecule for one ferredoxin I subunit. The ionic strength dependence of the cross-linking and the absence of a covalent reaction when ferredoxin is replaced by another acidic protein suggest that this covalent complex is a valid model of the native non-covalent complex. The study of its physiological activities indicates the existence of one or several other interacting sites on cross-linked cytochrome and would explain the role of the multihemic cytochrome.