The mechanism of the conservation of energy of biological oxidations

Abstract

In a recent review 111, it was pointed out that in tracing the development of concepts of the mechanism of respiratorychain phosphorylation over a period ofmore than thirty years, four distinct eras can be distinguished in succession, during which one or at most two hypothesis dominated the thinking of workers in this field. These eras were termed: (a) the era of the non-phosphoryhted intermediate; (b) the era of the 'conformational' hypothesis; (c) the era of the chemiosmotic hypothesis (delocalized protons); (d) the era of localized protons. Implicit in this statement is that we are now in the era of localized protons. However, a number of caveats need to be entered. First, since there is a considerable time lag before a current hypothesis enters the text books, these are still practically unanimous in presenting only the chemiosmotic hypothesis. For most of those not directly involved in bioenergetic research, and indeed for many who are, we are still in the era of this hypothesis, even though the possibility of some form of localized protons as the intermediate of oxidative phosphorylation dominates current discussion of the mechanism. Secondly, the review in question dealt specifically with the mechanism of ATP synthesis and not with other ways in which energy is conserved, that may still be adequately described by the chemiosmotic hypothesis. Thirdly, in that review a hypothesis was proposed that contains features of all four hypotheses listed [l]. In this review, 1 shall not repeat the description of the first two hypotheses nor of the evidence in support of the chemiosmotic hypothesis, in which A F H + (difference in electrochemical potential of protons across the energy-transducing membrane) is the obligatory intermediate in oxidative