Cytochromes of the green sulfur bacterium Chlorobium vibrioforme f. thiosulfatophilum. Purification,characterization and sulfur metabolism

Three cytochromes of the thiosulfate-utilizing green sulfur bacterium Chlorobium vibrioforme f. thiosulfatophilum were highly purified by ion exchange column chromatography and ammonium sulfate fractionation. All three cytochromes are located in the soluble fraction. Cytochrome c-551 (highest purity index obtained: A₂₈₀/A₄₁₆=0.39) shows maxima at 551 nm (-band), 521 nm (-band), and 416 nm (-band) for the reduced form. This cytochrome is an acidic protein with a molecular weight of 32,000, a redox potential of 150 mV, and an isoelectric point at pH 6.0. Cytochrome c-553 (highest purity index obtained: A₂₈₀/A₄₁₇=0.8) is also an acidic protein with maxima at 553,5 nm, 523,5 nm and 417 nm for the reduced form, a molecular weight of 63,000, a redox potential of 90 mV, an isoelectric point at pH 6.3, and it contains FAD as flavin component. It is autoxidizable and participates in sulfide oxidation, but cannot catalyze the reverse reaction. The cytochrome c-555 (highest purity index obtained: A₂₈₀/A₄₁₈=0.16) is a small basic protein with maxima at 555 nm, 523 nm and 418 nm (reduced form), a molecular weight of 12,500, an isoelectric point between pH 10 and 10.5, and a redox potential of 155 mV. The ratio of the cytochrome contents to each other is constant and does not change when the organism has only thiosulfate or sulfide as the main electron donor in the medium.The soluble fraction further contains the non-heme ironcontaining proteins rubredoxin and ferredoxin. The anaerobic sulfide oxidation in a growing culture of Chlorobium vibrioforme f. thiosulfatophilum is accompanied by a rapid formation of thiosulfate, which is only utilized when sulfide is no longer available, while the elemental sulfur concentration increases constantly until thiosulfate is consumed.Non-common abbreviations C Chlorobium - SDS sodium dodecylsulfate - HIPIP high-potential-iron-sulfur-protein