Photosynthesis in Rhodospirillum rubrum. 3. Metabolic control of reductive pentose phosphate and tricarboxylic acid cycle enzymes.

Enzymes of the reductive pentose phosphate cycle including ribulose-diphosphate carboxylase, ribulose-5-phosphate kinase, ribose-5-phosphate isomerase, aldolase, glyceraldehyde-3-phosphate dehydrogenase and alkaline fructose-1,6-diphos-phatase were shown to be present in autotrophically grown Rhodospirillum rubrum. Enzyme levels were measured in this organism grown photo- and dark heterotrophically as well. Several, but not all, of these enzymes appeared to be under metabolic control, mediated by exogenous carbon and nitrogen compounds. Light had no effect on the presence or levels of any of these enzymes in this photosynthetic bacterium. The enzymes of the tricarboxylic acid cycle and enolase were shown to be present in R. rubrum cultured aerobically, autotrophically, or photoheterotrophically, both in cultures evolving hydrogen and under conditions where hydrogen evolution is not observed. Light had no clearly demonstrable effect on the presence or levels of any of these enzymes.