Studies on effects of certain quinones. III. Photosynthetic ¹⁴CO₂ incorporation by Rhodospirillum rubrum

Substituted naphthoquinones, 2,3,-dichloro-1,4-naphthoquinone, and 2-methyl-1,4-naphthoquinone produced marked changes in the pattern of ¹⁴C-distribution during ¹⁴CO₂-fixation by photosynthetic bacterium Rhodospirillum rubrum. The most obvious change in the labeling pattern during photoautotrophic ¹⁴CO₂-fixation was a several-fold increase in 3-phosphoglyceric acid accompanied with a decrease in the amount of glutamate. In photoheterotrophic cells, quinones caused an appreciable increase in ¹⁴C-glycolic acid and concomitant decrease, although not proportional, in the amount of ¹⁴C-sugar phosphate. The level of ¹⁴C-incorporated in poly-β-hydroxybutyrate and ether-extractable lipids was considerably decreased in photoautotrophic and photoheterotrophic cells treated with quinones. The ability of quinones to interfere with the synthesis of NADH and ATP, and their ability to interact with sulfhydryl enzymes and coenzymes appears to be responsible for the changes observed.