On the extent of localization of the energized membrane state in chromatophores from Rhodopseudomonas capsulata N22

Abstract

1. The principle of the double-inhibitor titration method for assessing competing models of electron transport phosphorylation is expounded. 2. This principle is applied to photophosphorylation by chromatophores from Rhodopseudomonas capsulata N22. 3. It is found that, in contrast to the predictions of the chemiosmotic coupling model, free energy transfer is confined to individual electron transport chain and ATP synthase complexes. 4. This conclusion is not weakened by arguments concerning, the degree of uncoupling in the native chromatophore preparation or the relative number of electron transport chain and ATP synthase complexes present. 5. Photophosphorylation is completely inhibited by the uncoupler SF 6847 at a concentration corresponding to 0.31 molecules per electron transport chain. 6. The apparent paradox is solved by the proposal, consistent with the available evidence on the mode of action of uncouplers, that uncoupler binding causes a co-operative conformation transition in the chromatophore membrane, which leads to uncoupling and which is not present in the absence of uncoupler.

Determination of the Proton Electrochemical Gradient across Biological Membranes

“…Similar conclusions have been drawn from double-inhibitor titration studies (Baum et al, 1971;Hitchens and Kell, 1982a;Westerhoff et al, 1982). Similar conclusions have been drawn from double-inhibitor titration studies (Baum et al, 1971;Hitchens and Kell, 1982a;Westerhoff et al, 1982).…”

The Roles of Osmotic Stress and Water Activity in the Inhibition of the Growth, Glycolysis and Glucose Phosphotransferase System of Clostridium pasteurianum

“…Glucose was added to a concentration of 20 mM. All procedures were done anaerobically, and pH changes were recorded in a vessel (Hitchens & Kell, 1982), and using the apparatus (Hitchens & Kell, 1984), described previously. The reaction volume was 8 ml and the temperature was 37 "C. Other media and additions are given in the legends to Figures.…”

A model system for delocalized chemiosmotic coupling exhibited the features thought diagnostic of localized coupling

“…that proton leakage is insignificant; cf. Hitchens & Kell (1982a)], or [Westerhoff et al, 1983a;Van der Bend et al, 1985;Westerhoff & Van Dam, 1986] an improved formulation of the rules of thumb (the results obtained in our reconstituted system do differ systematically from those obtained in the more physiological systems). Hans V. WESTERHOFF NIH, Building 2, Room 319, Bethesda, MD 20892,…”

“…Does this prove that free-energy transduction is organized in a delocalized fashion? Of course not: our contentions merely prove that double-inhibitor experiments plus the rules of thumb as they have been formulated by Hitchens & Kell (1982a cannot serve as sole evidence that energy coupling is organized in a localized fashion. In interpreting this type ofexperiment one needs additional knowledge of the system [e.g.…”

“…For delocalized coupling, Hitchens & Kell's (1982a) rule of thumb for ii experiments has been that the potency be reduced; for ui experiments, that the potency of the uncoupler not be increased. Baum et al (1971Baum et al ( , 1978, Hitchens & Kell (1982a,b, 1983a and we (Westerhoff et al, 1983a,b) found that experimental results in actual energy-coupling systems conflicted with these rules of thumb. This has been taken as evidence against delocalized coupling.…”