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Title

Photoreaction center of Ectothiorhodospira sp. Pigment, quinone, and polypeptide composition

AuthorsLefebvre, Suzie; Picorel Castaño, Rafael ; Cloutier, Yves; Gingras, Gabriel
Issue Date1984
PublisherAmerican Chemical Society
CitationBiochemistry 23 (22): 5279-5288 (1984)
AbstractThe photoreaction center of Ectothiorhodospira sp., a member of the family Chromatiaceae, was isolated from its photosynthetic membranes with a yield of approximately 25-35%. The preparation is free of antenna bacteriochlorophyll and associated proteins. Its pigment complement is 4 mol of bacteriochlorophyll, 2 mol of bacteriopheophytin, and 1 mol of spirilloxanthin. On this basis, its molar extinction coefficient was calculated. Whereas chromatophores contain both ubiquinone and menaquinone, the photoreaction center contains only menaquinone, which, therefore, probably is the primary electron acceptor. The protein is composed of three different subunits of apparent molecular weights of 39 100, 31 300, and 24 800. The sum of these weights is very close to the protein minimal molecular weight of the photoreaction center based on its molar extinction coefficient and amino acid content. This indicates a 1:1:1 molar stoichiometry. Four moles of heme c per mole of photoreaction center and cytochromes c-555 and c-552 are also present. Specific staining after polyacrylamide gel electrophoresis shows that all the heme is bound to the 39K polypeptide. A good amino acid composition homology is found between the L and M polypeptides from Ectothiorhodospira sp. and from Rhodospirillum rubrum. A membrane-bound cytochrome from Chromatium vinosum seems to be homologous to the heaviest subunit of the former two organisms.
Publisher version (URL)http://dx.doi.org/10.1021/bi00317a028
URIhttp://hdl.handle.net/10261/96117
DOI10.1021/bi00317a028
Identifiersdoi: 10.1021/bi00317a028
issn: 0006-2960
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