Cytochromes and anaerobic sulfide oxidation in the purple sulfur bacterium chromatium warmingii

Abstract

Two soluble acidic c-type cytochromes –c′ and c-552–were isolated by ion exchange chromatography, gel filtration and ammonium sulfate fractionation.Cytochrome c′ is a high-spin cytochrome with maxima at 399nm, 490nm, and 634nm in the oxidized form and at 550nm, 425nm and a characteristic shoulder at 434nm in the reduced state. The best purity index obtained (A280/A399) was 0.35.Cytochrome c′ is autoxidizable, has am olecular weight of 12000(estimated by sodium dodecylsulfate electrophoresis), am idpoint redoxpotential of +10mV and an isoelectric point at pH 4.0.The reduced cytochrome c′ reacts with carbon monoxide.The reaction is reversible.Cytochrome c-552 shows maxima at 552nm, 523nm and 417nm in the reduced form and at 408nm inthe oxidized state.The best purity index obtained (A280/A408) was 0.94.Cytochrome c-552 has a molecular weight of 30000 and an isoelectric point between pH 4.3 and 5.0. Chromatium warmingii also contains amembrane-bound cytochrome c-552.During anaerobic sulfide oxidation, elemental sulfur and sulfate were formed at the same time.When all sulfide was consumed bythe cells, the remaining intracellular elemental sulfur was further oxidized to sulfate. © 1983, Walter de Gruyter. All rights reserved.