Molecular Properties of High Potential Iron Sulfur Protein of Chromatium warmingii

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Abstract
High potential iron sulfur protein (HIPIP) of the purple sulfur bacterium C. 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 .mu.mol 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 8900 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 midpont redox potential of +355 mV. One mole of HIPIP contains 4 mol nonheme iron and 4 mol acid-labile sulfur.