Photosynthesis in Rhodospirillum rubrum. I. Autotrophic carbon dioxide fixation.

The incorporation and distribution of activity from (14)CO(2) was investigated under autotrophic conditions in the facultative photoautotroph, Rhodospirillum rubrum, with cells cultured on hydrogen, carbon dioxide, and ammonium sulfate. In 1 second (14)CO(2) fixation experiments essentially all of the activity was found in 3-phosphoglyceric acid: plotted against time percent incorporation into phosphate esters has a strikingly negative slope. These results suggest that under autotrophic conditions the reductive pentose phosphate cycle or the key reactions of the cycle play a major role in carbon metabolism in this photosynthetic bacterium. Incorporation into amino acids and into intermediates of the tricarboxylic acid cycle was quite low.