Studies on the electron-transfer systems in photosynthetic bacteria IV. Kinetics of light-induced cytochrome reactions and analysis of electron-transfer paths

The light-induced cytochrome reactions and dark steady state changes were studied in photosynthetic bacteria, Chromatium and Rhodospirillum rubrum. The effects of external substrates, reducing agents, inhibitors, O₂ tension etc. on the kinetics and the steady state changes of the cytochrome reactions are presented.

The pattern of electron transfer in the bacterial systems changed markedly under different conditions. O₃ was one of the key factors to control the patterns. In general, apparently “non-cyclic” cytochrome response was observed under the growing conditions; on the other hand, ‘cyclic” or “closed-chain” type characteristics were observed under non-growing aerobic conditions. Kinetic analysis indicated that heptylhydroxyquinoline-N-oxide had an interaction with the reaction of cytochrome c and cytochrome b as had been postulated from difference spectra. Cross-over of the photochemical oxidation and photochemical reduction was observed in the presence of the inhibitor. It was indicated that ascorbate and trichlorophenolidophenol (added singly or combined) did not compete effectively with the internal photochemical reducing system and did not change the steady state of cytochromes. Under certain conditions, however, ascorbate plus trichlorophenolindophenol shifted the steady state of cytochrome b. The formation of an electron-transfer by-pass by N-methylphenazonium methosulfate was confirmed.

Direct interaction of bacteriochlorophyll and cytochrome molecules was postulated in the heptylhydroxyquinoline-N-oxide-insensitive rapid “light-off” reaction or aerobic cells, as well as in the rapid phase of the light-induced oxidation of cytochrome. The possibility of the control of electron transfer by concentration of adenosine phosphates was also discussed.