Reactions driven by an electrochemical potential

If ATP reversal operates via the intermediate formation of an electrochemical proton gradient, as the chemiosmatic hypothesis predicts, it should be possible to show the same reverse reaction by the direct imposition of a transmembrane electrochemical proton gradient of the proper polarity. 

Indeed, acid-base transition induces reduction of [76]. The reduction is transient, does not require addition of an external electron donor, but is dependent upon the presence of reduced carriers between the two photosystems which act as electron donors for the transient reduction [82,83]. 

An acid-base transition also drives reversal of the PS Il-induced charge separation indicated by luminescence [84]. The reaction again requires preprovision of an oxidized partner by preillumination, and is stimulated by a simultaneously imposed electric potential gradient of the proper polarity [85]. 

During the last thirty years, intensive investigations by numerous laboratories converted photophosphorylation from a highly debatable and marginally detectable process to a well-established and well-dissected reaction. We have today a wealth of information about the overall photochemical steps, the electron transport reactions driven by it, the electrochemical gradient driven by the electron transport, and the overall reaction responsible for ATP synthesis by the enzyme-bound ATP 

17 Trebst, A. and Avron, M. (eds.) (1977) Photosynthetic Electron Transport and Photophosphorylation, Encyclopedia of Plant Physiology, New Series, Vol. 5, 820 pp., Springer-Verlag, Heidelberg. 

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