Biosynthesis of phenylalanine from phenylacetate by Chromatium and Rhodospirillum rubrum.

Cultures of Chromatium strain D and Rhodospirillum rubrum incorporated (14)C from phenylacetate-1-(14)C during anaerobic growth. The radioactivity in the protein fraction of cells was mainly in phenylalanine. Phenylalanine from Chromatium cells grown in phenylacetate-1-(14)C was labeled at carbon 2. Incorporation of phenylacetate by Chromatium was decreased in the presence of exogenous phenylalanine, and de novo synthesis of phenylalanine from bicarbonate was less in medium containing either phenylalanine or phenylacetate. These organisms, and also certain anaerobic rumen bacteria, apparently carboxylate phenylacetate to synthesize the phenylalanine carbon skeleton. The mechanism of the carboxylation is unknown; however, it appears to be dependent upon anaerobic conditions, since R. rubrum did not synthesize phenylalanine from phenylacetate during aerobic growth in the dark.