Purification and characterization of triheme cytochrome c7 from the metal-reducing bacterium, Geobacter metallireducens.

A soluble c-type cytochrome was first purified from Geobacter metallireducens to an electrophoretically homogeneous state. The purified cytochrome c showed absorption peaks at 530 and 409 nm in the oxidized form and 552, 522, and 418 nm in the reduced form. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate allowed us to calculate the molecular mass at 9.5 kDa. It contained 3 mol of heme c per molecule of the protein on the basis of heme c and protein concentration. The mid-point redox potential at pH 7.0 was determined to be -190 mV. Although the N-terminal amino acid sequence of the first 17 residues was similar to that of Desulfuromonas acetoxidans cytochrome c7, G. metallireducens cytochrome c did not show Fe(III)-reducing activity.