Characterization of DorC from Rhodobacter capsulatus, a c-type cytochrome involved in electron transfer to dimethyl sulfoxide reductase

The dorC gene of the dimethyl sulfoxide respiratory (dor) operon of Rhodoba cter capsulatus encodes a pentaheme c-type cytochrome that is involved in e lectron transfer from ubiquinol to periplasmic dimethyl sulfoxide reductase , DorC was expressed as a C-terminal fusion to an 8-amino acid FLAG epitope and was purified from detergent-solubilized membranes by ion exchange chro matography and immunoaffinity chromatography, The DorC protein had a subuni t M-r = 46,000, and pyridine hemochrome analysis indicated that it containe d 5 mol heme c/mol DorC polypeptide, as predicted from the derived amino ac id sequence of the dorC gene. The reduced form of DorC exhibited visible ab sorption maxima at 551.5 nm (alpha-band), 522 nm (beta-band), and 419 nm (S oret band). Redox potentiometry of the heme centers of DorC identified five components (n = 1) with midpoint potentials of -34, -128, -184, -185, and -276 mV, Despite the low redox potentials of the heme centers, DorC was red uced by duroquinol and was oxidized by dimethyl sulfoxide reductase.