No abstract

No abstract

No abstract

No abstract

Observations on the direction of proton translocation coupled to photo-oxidoreduction and to respiration show that in chromatophores (or sonic particles) of Rhodospirillurn rubrum and Rhdopseudomonm spheroides the direction is inwards, but in the intact organisms the direction is outwards. The relative proton translocation activities associated with photo-oxidoreduction and respiration appear to depend on the relative extent of developmcnt of the alternative pigment systems produced during growth.The direction of proton translocation associated with the oligomycin-sensitive ATPase activity in chromatophores of R. rubrunz was the same as that associated with photo-oxidoreduction or respiration, suggesting that the proton current generated either by light or by respiration might alternatively drive ATP synthesis.Proton translocation, associated with photo-oxidoreduction or respiration, is directed outwards in intact A d a m variabilis.Respiration and ATP hydrolysis in intact mitochondria are coupled t o the outward translocation of protons [l, 21. Similarly, respiration in certain bacteria is coupled to outward proton translocation [3]. I n chloroplasts [4,5] and in bacterial chromatophores [6-81, on the other hand, photo-oxidoreduction is coupled to the inward translocation of protons.If it were true, as required by the chemiosmotic hypothesis, that ATP synthesis is caused by driving the proton-translocating ATPase of the coupling membrane backwards with a current of protons, in photosynthetic bacteria such as Bhodospirillum rubrum, which can synthesise ATP either photosynthetically or by respiration, the proton current coupled to photo-oxidoreduction should have the same polarity as the proton current coupled to respiration. E'urther, the polarity of proton translocation should be the same for oxidoreduction as for ATP hydrolysis. It was previously shown by Mitchell and Moyle [9]that sonic particles of beef heart mitochondria were of the opposite polarity to the intact mitochondria with respect to proton translocation driven by respiration and ATP hydrolysis. The question therefore arose as to whether proton translocation in intact photosynthetic bacteria had the same polarity as in the chromatophores produced by sonic disintegration, or whether the chromatophores were effectively inside out. It was also desirable to compare the polarity of proton translocation in the grana or lamellae of chloroplasts of higher plants with that across the membranes of more primitive organisms such as blue-green algae and bacteria. The light falling on the culturcs was estimated, using a Weston Master V light meter, to be 250 foot candles. Under these conditions, growth was exponential up to an absorbance at 750 mp of 1.5. Cells were harvested late in the exponential phase of growth.Rps. spheroides was grown aerobically in the dark a t 28" in 10-litre flasks containing 1 litre of medium S. Cultures were started with a 0.3O/, inoculum of exponential phase photosynthetically grown subculture and harvested a t about 1 mg dry weight...