Partial purification and characterization of two soluble c-type cytochromes from Chromatium vinosum

Abstract

Two c-type cytochromes from Chromatium vinosum have been partially purified and characterized. Cytochrome c 550, which appears to function as an electron carrier in the cyclic electron transport chain of this photosynthetic purple sulfur bacterium, has a molecular weight of approximately 15,000 and an oxidation-reduction midpoint potential ( E m) of + 240 mV at pH 7.4. It has (in the reduced form) an α band at 550 nm and a β band at 520 nm. Cytochrome c 551 is characterized by absorbance maxima at 354 and 409 nm in the oxidized form and 418, 523, and 551 nm in the reduced form. The reduced cytochrome reacts with CO. Cytochrome c 551 is a monomeric protein with a molecular weight of 18,800 ± 700 and E m = −299 ± 5 mV (pH independent between pH 6.3 and 8.0). It appears to lack a methionine axial ligand as indicated by the absence of an absorbance band at 695 nm in the oxidized form.