Isolation and characterization of a high molecular weight cytochrome from the sulfate reducing bacterium Desulfovibrio gigas.

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 e533 (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.