Studies on the biosynthesis of porphyrin and bacteriochlorophyll by Rhodopseudomonas spheroides. 1. The effect of growth conditions

Abstract

Rhodopseudomonas spheroides was grown either aerooicany in the dark or anaerobically in the light with suboptimum amounts of biotin. These cultures formed porphyrlns and bacterlochlorophyll when illuminated in the presence of [alpha]-oxoglutarate and glycine only when biotin was added at this stage. The same results were obtained when succinate was substituted for [alpha]-oxoglutarate. There was a close association between growth, as determined by dry weight, and the formation of porphyrins and bacteriochlorophyll. Deficiency of nicotinlc acid or thiamine affected dry weight and porphyrin and bacteriochlorophyll formation in the same way as deficiency of biotin. Organisms deficient in biotin, nicotinic acid or thiamine had decreased amounts of bacterio-chlorophyll/unit dry weight The concentration of carotenolds as determined in biotin-deficient orgasisms was found to be reduced. Chromatophores from these organisms also showed a reduced concentration of bacterlochlorophyll and of the yellow carotenold but little change in other components measured. Extracts of organisms deficient in any of the 3 vitamins or grown with acetate in place of malate showed a marked reduction in the activity of aminolaevulate synthetase and in some cases of aminolaevulate dehydratase. There was no significant change in L-theronine dehydrogenase, D-[beta]-hydroxybutyric dehydrogenase or L-alanine-[gamma] [image]-dloxovalerate amlnotransferase where these were determined. A preparation of commercial avidin inhibited aminolaveulate synthetase. Preincubatlon with biotin did not abolish this inhibition. On further purification the inhibitory power of avidin decreased and finally disappeared. It is therefore believed that biotin is not directly concerned in the synthesis of aminolaevulate. It is concluded that the synthesis of bacteriochlorophyll and growth are linked in some unknown manner; but additional mechanisms exist to regulate the synthesis of porphyrins and bacteriochlorophyll including inhibition and repression of aminolaevulate synthetase.