Isolation and characterization of a high molecular weight cytochrome from the sulfate reducing bacteriumDesulfovibrio gigas

Abstract

A high molecular weight c‐type cytochrome (Hmc) was purified and characterized from Desulfovibrio gigas. The molecular weight was estimated to be 67 kDa by SDS‐PAGE and its N‐terminus is homologous to those of the 16 hemes containing high molecular weight cytochrome c from Desulfovibrio vulgaris strains Hildenborough and Miyazaki. The purified hemoprotein shows c‐type cytochrome absorption spectrum with ε₅₅₃(red) = 368 mM⁻¹ · cm⁻¹. A band at 640 nm, characteristic of high‐spin hemes, was detected. The EPR spectra show the presence of two high‐spin heme species, plus several non‐equivalent low‐spin hemes. The heme reduction potentials, at pH 7.6, range from −50 mV to −315 mV. In contrast to what has been described for D. vulgaris Hmc, the protein isolated from D. gigas directly accepts electrons from hydrogenase and further reduces other redox proteins.