Relevance of Proton Uptake induced by Light to the Mechanism of Energy Coupling in Photophosphorylation

Abstract

THE relevance of proton movements which are dependent on energy to energy conservation mechanisms in oxidative phosphorylation and photophosphorylation has recently been extensively debated, particularly with respect to the “chemiosmotic”^1,2 and chemical^3,4 hypotheses. There are a few critical tests of the chemiosmotic theory. These include: (a) the ratio of protons taken up to electrons transported; the value of this H⁺: e⁻ ratio should equal the number of sites of energy conservation in the election transport path; (b) the effect of phosphorylating conditions; during phosphorylation one should observe a fall in the steady state extent of the proton gradient, as a result of the stoichiometric utilization of one or two protons² per ATP synthesized. Reversible _pH changes in spinach chloroplasts induced by light have previously been described in detail^5,6. This communication reports experiments designed to test the chemiosmotic theory by these criteria. The results cannot be reconciled with the theory as it is at present conceived.