Control of porphyrin synthesis in Rhodopseumomonas spheroides

Abstract

1. 1. Photosynthetic cultures of Rhodopseudomonas spheroides strain Ga, deprived of sulphur do not form bacteriochlorophyll, but do excrete porphyrins. The same is true of cultures of strain M-17 which requires methionine, when deprived of this amino acid. 2. 2. Cultures of strain Ga starved for sulphur and cultures of strain M-17 starved for methionine excrete porphyrins despite increase in light intensity, prevention of protein synthesis, or certain low oxygen tensions, all of which are known to inhibit bacteriochlorophyll synthesis without causing porphyrin excretion. 3. 3. Step-up in light intensity, inhibition of protein synthesis, or certain oxygen tensions which inhibit bacteriochlorophyll synthesis do not prevent strain Ga from converting δ-aminolevulinic acid to porphyrins, even in the presence of methionine and sulphur. These results are interpreted as indicating that control over porphyrin synthesis occurs by a “feed-back” inhibition of δ-aminolevulinic acid synthesis. We suggest that the inhibitor is a precursor of bacteriochlorophyll, that its synthesis requires methionine, and that its conversion to bacteriochlorophyll is prevented by inhibition of protein synthesis, by increase in light intensity, or by oxygen. 4. 4. High oxygen tensions, unlike increase in light intensity or inhibitor of protein synthesis, bring about an inhibition of the conversion of δ-aminolevulinic acid to porphyrins. This suggests that there is an additional control of porphyrin synthesis besides the proposed feedback regulation of δ-aminolevulinic acid formation. 5. 5. Chloromycetin was found to inhibit formation of porphyrins from δ-aminolevulinic acid; this is not due to inhibition of protein synthesis.