High potential iron sulfur protein (HIPIP) of the purple sulfur bacterium Chromatium warmingii was purified to homogeneity by ion exchange chromatography, gel filtration and ammonium sulfate fractionation. The acidic protein was isolated in the reduced form. The best purity index (A280/A388) obtained was 2.52, and 3.8 μmol of the protein was isolated out of 100 g wet cell material. The molecular weights estimated by sodium dodecylsulfate polyacrylamide gel electrophoresis and gel filtration through Sephacryl S-200 were 8 900 and 10 500, respec­tively. The protein has an isoelectric point at pH 3.6 for the reduced form and at pH 3.8 for the oxidized form, and a midpoint redox potential of +355 mV. One mol of HIPIP contains 4 mol nonheme iron and 4 mol acid-labile sulfur

Chromatium warmingii, Cytochrome c', Cytochrom e c-552, A naerobic Sulfide O xidation, Phototrophic Bacteria Two soluble acidic c-type cytochromes -c' and c-552 -were isolated by ion exchange chromatography, gel filtration and amm onium sulfate fractionation. Cytochrom e c' is a high-spin cytochrome with maxima at 399 nm, 490 nm, and 634 nm in the oxidized form and at 550 nm, 425 nm and a characteristic shoulder at 434 nm in the reduced state. The best purity index obtained (^280/^399) was 0.35. Cytochrome c' is autoxidizable, has a m olecular weight of 12000 (estimated by sodium dodecylsulfate electrophoresis), a m idpoint redoxpotential o f + 10m V and an iso electric point at pH 4.0. The reduced cytochrome c' reacts with carbon monoxide. The reaction is reversible. Cytochrome c-552 shows maxima at 552 nm, 523 nm and 417 nm in the reduced form and at 408 nm in the oxidized state. The best purity index obtained (^280/^408) 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 a m em brane-bound cytochrom e c-552. D uring anaerobic sulfide oxidation, elemental sulfur and sulfate were formed at the sam e time. W hen all sulfide was consumed by the cells, the remaining intracellular elemental sulfur was further oxidized to sulfate. IntroductionReduced sulfur compounds, like sulfide or thiosulfate, are used as electron donors for anoxygenic photosynthesis by phototrophic sulfur bacteria [1,2]. Electron transfer proteins, like cytochromes or high potential iron sulfur proteins, are generally involved in sulfur metabolism in purple and green sulfur bacteria [2,3], The m olecular properties of cytochromes, their distribution and their function in sulfide and thiosulfate oxidation in green sulfur bacteria (Chlorobiaceae) have been intensively studied [4][5][6][7][8][9][10][11][12][13], In these organisms, flavocytochromes act as sulfide: cytochrome c reductases [7,[9][10][11], Cytochrome c-551, only present in the thiosulfate utilizing Chlorobium limicola f thiosulfcitophilum [6,9] and Chlorobium vibrioforme f. thiosulfatopliilum [11] is the only endogenous electron acceptor in thiosulfate oxidation. A small Abbreviations: Chr. Chromatium ; APS, adenylylsulfate; SDS, sodium dodecylsulfate.Reprint requests to Dr. U. Fischer.0341-0382/83/1100-0960 $ 0 1 .3 0 /0 cytochrome c-555, com parable to plant /-type cyto chromes, was found in all green sulfur bacteria and functions as an electron mediator. It accepts the electrons from both cytochromes mentioned above and carries them to bacteriochlorophyll [8,9,13].Cytochromes of the purple sulfur bacteria (Chromatiaceae) have been isolated so far only from small-cell species, like Chromatium vinosum [14][15][16][17] U. Wermter and U. Fischer • Cytochromes and Anaerobic Su lfid e O xidation in Chromatium warmingii 961cytochrome content. The aim of this study was, to isolate and to characterize the cytochromes of Cliromatium warmingii and to com pare the results with those of the small-cell Ch...