THE PHOTOASSIMILATION OF SUCCINATE TO HEXOSE BY RHODOSPIRILLUM RUBRUM

Abstract

A pathway for the synthesis of hexose from succinate by R. rubrum is proposed. With 2,3 -C14 2-labelled succinate and fumarate as iubstrates in experiments with chromatophores and a soluble enzyme fraction of R. rubrum, it was found that the products of succinate metabolism by the extracts were the same as in whole cells and that the light-dependent oxidation of succinate was catalyzed by the chromatophores. All the other enzymes involved were in the soluble fraction. The presence of all the enzymes required for the proposed pathway was demonstrated in the extracts and their specific activities measured. The overall rate of succinate assimilation was measured manometrically. The activities of the enzymes account for the overall rate of assimilation. The proposed pathway represents the major mechanism for synthesis of hexose from succinate in R. rubrum. The formation of alanine and aspartate was observed in experiments with isotopically labelled substrates, and possible synthetic pathways for these compounds are discussed.