Generation of succinyl-coenzyme A in photosynthetic bacteria
- 139 Downloads
Pathways of succinyl-Coenzyme A (succinyl-CoA) formation in various photosynthetic bacteria were investigated through several approaches, including determination of activity levels of relevant enzymes. Extracts of photosynthetically grown cells of representative Rhodospirillaceae and Chromatium vinosum showed α-ketoglutarate dehydrogenase (KGD) activities sufficient to account for generation of the succinyl-CoA required for biosynthetic metabolism. Except as noted below, the observed ratios of fumarate reductase/succinate dehydrogenase activities were low, consistent with the conclusion that these organisms produce succinyl-CoA oxidatively from α-ketoglutarate (KG), rather than by reductive metabolism of fumarate. On the other hand, the green bacterium Chlorobium limicola appears to produce succinyl-CoA by the reductive pathway; in this organism, KGD activity could not be detected, and a high fumarate reductase/succinate dehydrogenase ratio was observed. Results obtained with Rhodopseudomonas gelatinosa suggest that this otherwise typical member of the Rhodospirillaceae may be able to generate succinyl-CoA via both “arms” of the citric acid cycle, that is, oxidatively from KG, and reductively from fumarate. To further explore the several physiological roles of the conversion: KG→succinyl-CoA in Rhodopseudomonas capsulata, a mutant (strain KGD 11) almost completely blocked in KGD activity was isolated and studied in detail. Under anaerobic photosynthetic conditions, KGD 11 grows readily on succinate as the sole carbon source; in contrast to the wild type parent, however, it cannot grow with l-glutamate as the source of carbon. The R. capsulata parental strain can grow in darkness as an aerobic heterotroph on various carbon/energy sources including pyruvate, D,L-malate, or succinate. Mutant KGD 11, however, is unable to grow aerobically on the substrates noted. These results indicate that the energy for aerobic dark growth of R. capsulata is provided by ”respiratory phosphorylation” fueled by citric acid cycle function, and that this requires a substantial level of KGD activity. The present findings also indicate that citric acid cycle sequences in most of the Rhodospirillaceae prominently used in current research are geared to operate in the oxidative direction, as in nonphotosynthetic aerobic heterotrophs.
Key wordsPhotosynthetic bacteria Succinyl-Coenzyme A α-Ketoglutarate dehydrogenase Fumarate reductase Succinate dehydrogenase
Unable to display preview. Download preview PDF.
- Arrigoni O, Singer TP (1962) Limitations of the phenazine methosulphate assay for succinic and related dehydrogenases. Nature 193:1256–1258Google Scholar
- Bose SK, Gest H (1962) Hydrogenase and light-stimulated electron transfer reactions in photosynthetic bacteria. Nature 195:1168–1171Google Scholar
- Dawson RMC, Elliott DC, Elliott WH, Jones KM, (eds) (1969) Data for biochemical research. Oxford University Press, New York Oxford, pp 196–197Google Scholar
- Gest H (1980) The evolution of biological energy-transducing systems. FEMS Microbiol Lett 7:73–77Google Scholar
- Meynell GG, Meynell E (1970) Theory and practice in experimental bacteriology. Cambridge University Press, Cambridge, pp 257–259Google Scholar
- Miller JH (1972) Experiments in molecular genetics. Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, pp 130–134Google Scholar
- Niel CB van (1971) Techniques for the enrichment, isolation and inaintenance of the photosynthetic bacteria. In: San Pietro A (ed) Methods in Enzymology, vol 23A, Academic Press, New York London, pp 3–28Google Scholar
- Pfennig N (1965) Anteicherungskulturen für rote und grüne Schwefelbakterien. Zentbl Bakteriol Parasitenkde Infektionskr-Hyg Abt 1, Suppl 1:179–189Google Scholar
- Reed LJ, Mukherjee BB (1969) α-Ketoglutarate dehydrogenase complex from Escherichia coli. In: Lowenstein JM (ed) Methods in Enzymology. vol 13, Academic Press New York London, pp 55–61Google Scholar