The association of protein synthesis with formation of pigments in some photosynthetic bacteria

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Abstract
The antimetabolites ethionine, 8-azaguanine and 5-fluorouracil preferentially inhibited the synthesis of bacteriochloro-phyll and of carotenoids by cultures of Rhodopseudomonas spheroides growing photosynthetically. The chromatophores synthesized in the presence of these antimetabolites had a decreased content of the photo-synthetic pigments. They preferentially inhibited synthesis of [delta] -amino-laevulate synthetase but not succinate dehydrogenase, succinate thio-kinase or alkaline phosphatase. The synthesis of photosynthetic pigments and [delta] -aminolaevulate synthetase by organisms incubated with low aeration was inhibited by ethionine, p-fluorophenylalanine, 8-azaguanine, 5-fluorouracil and chloramphenicol. A N source (added as NH4+ ions) was necessary for the maximal synthesis of bacteriochlorophyll by such suspensions. Suspensions of a mutant of R. spheroides required adenine and histidine for growth and for pigment synthesis when incubated with low aeration. The phenylalanine content of soluble and chromatophore protein in R. spheroides was similar. The rate of incorporation of [1- C] phenylalanine into protein fractions was similar in organisms growing either anaerobically in the light or aerobically in the dark. This preferential incorporation into chromatophore protein occurred only under conditions that permitted pigment synthesis. Incorporation dependent on a N source was inhibited by 8-azaguanine and chloramphenicol. The preferential incorporation is due largely to preferential turnover of the chromatophore fraction during the synthesis of the photosynthetic pigments.