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S Saphon

Publications and source records attributed to S Saphon.

4 recordsLinked to original sources
PubMed1975

The functional unit of electrical events and phosphorylation in chromatophores from Rhodopseudomonas sphaeroides.

1. From electron micrographs of chromatophores from Rhodopseudomonas spaeroides and from the estimated bacteriochlorophyll per chromatophore was estimated. The mean diameter of the chromatophore vesicles was 600 A. 2. The decay of the flash-induced electric potential across the chromatophore membrane measured by the carotenoid band shift was 20% accelerated by about one valinomycin molecule per 4700 bacteriochlorophyll, i.e. by one ionophore molecule per chromatophore. 3. The inhibition of the flash-induced ATP formation by valinomycin followed a similar pattern to the accelerated decay of the electric potential. 4. The single turnover flash yield of ATP synthesis gave a mean value of one ATP per 1470 bacteriochlorophyll or about 3 ATP per vesicle. 5. With regard to the partitioning of the ionophore between the membrane (85%) and aqueous phase (15%) we conclude that one molecule of valinomycin per chromatophore is sufficient to begin to collapse the electrical potential and inhibit ATP synthesis. It is therefore suggested that the membrane potential is an essential component of the energized state which is used for phosphorylation. The results correspond to those obtained for the 100-fold larger vesicles in chloroplasts (thylakoids) where one molecule of ioophore is also sufficient to quench both events.

Adenosine Triphosphate↗
PubMed1975

Electrical potential changes, H+ translocation and phosphorylation induced by short flash excitation in Rhodopseudomonas sphaeroides chromatophores.

1. The basal decay of the carotenoid shift of chromatophores from photosynthetic bacteria following short flash excitation is approximately biphasic. The decay indicates the dissipation of the transmembrane electrical potential. 2. The H+ efflux following rapid H+ binding after a flash, measured from the colour change of added cresol red, shows very similar kinetics to the carotenoid shift decay suggesting that the dissipation of the electric potential decay is a consequence of the H+ efflux. 3. The electric potential decay is stimulated when the chromatophore suspension is supplemented with ADP and Pi (in either the presence or absence of antimycin A). 4. The stimulated electric potential decay by ADP and Pi has a similar pH dependence to that of phosphorylation in continuous light. 5. The stimulation of the electric potential decay by ADP and Pi is reversed, by aurovertin, an antibiotic which inhibits phosphorylation. 6. The stimulation of the electric potential decay by ADP+Pi is also reversed by the inhibitors oligomycin and venturicidin. These inhibitors, but not aurovertin, also inhibit the fast phase of the decay under non-phosphorylating conditions. 7. Valinomycin accelerates the overall rate of decay of the electric potential, inhibits the ADP and Pi stimulated electric potential decay, and inhibits the flash-induced phosphorylation. The decay rate of the H+ efflux however, is slower in the presence of this ionophore. 8. Nigericin-type ionophores accelerate the overall decay rate of the H+ efflux and inhibit the ADP and Pi stimulated electric potential decay. The basal rate of the electric potential decay is unaffected by treatment with these ionophores. 9. When a coupling factor associated with the chromatophore ATPase is removed from the membrane, both the stimulation of the electric potential decay by ADP and Pi and ADP phosphorylation are inhibtied. Both reactions are completely restored after reconstitution with the crude coupling factor extract. The basal electric potential decay rate is not affected by the removal of coupling factor.

Adenosine Diphosphate↗
PubMed1975

The extent of the stimulated electrical potential decay under phosphorylating conditions and the H+/ATP ratio in Rhodopseudomonas sphaeroides chromatophores following short flash excitation.

1. In chromatophores from Rps. sphaeroides, the stimulation by ADP and Pi of the electric potential decay indicated by the carotenoid shift is greater than the stimulation of the decay of pH change indicated by the colour change of added cresol red under similar conditions. This difference is attributed to H+ consumption during the synthesis of ATP. The ratio of H+ translocated across the membrane to ATP synthesized was estimated to be approximately 1.7 H+/ATP. 2. The stimulation of the electrical potential decay by ADP and Pi was found to be a constant fraction (10%) of the total decay when the flash intensity was varied. No 'critical' or 'threshold' potential was observed. 3. The stimulated electrical potential decay after a second flash, given within a few seconds of the first, was related to the amplitude of the electrical potential produced by the second flash (10%) but neither to the dark time between the flashes, nor to the total extent of the electrical potential above the dark level. These results are consistent with two hypotheses (a) the chromatophores are a mixed population of vesicles, only a small fraction (10%) of which possess an active ATP synthesizing system (b) the activity of the ATP synthesizing system, though driven by a proton motive force, is controlled by electron transport processess. If alternative (a) is correct then the overall single turnover flash yield of 1 ATP per 1470 bacteriochlorophyll measured in (1) would mean that the yield of the active vesicles is approximately 10 ATP per 1470 bacteriochlorophyll or 30 ATP per vesicle. 4. The stimulation of the electrical potential decay by ADP and Pi is approximately 40% less in antimycin-treated chromatophores. It is shown that this is probably a consequence of antimycin-inhibited H+-release on the inside of the chromatophore vesicles following a flash.

Adenosine Diphosphate↗