On proton-coupled information transfer along the surface of biological membranes and the mode of action of certain colicins

The colicins are a heterogeneous group of proteinaceous bactericidal agents produced by a variety of bacteria and active against many strains of Escherichia coli; many other bacteriocins active against other bacterial species, and exhibiting broadly similar properties to some of the colicins, have also been described (for review see [1-3]). As Plate has recently pointed out in a short review [4], certain of the colicins, especially those of the El, K and Ia types, which are known to disrupt membrane energy transduction processes in sensitive bacterial strains, may prove' extremely useful as probes of the nature of membrane energy transduction processes themselves. The purpose of the present article is threefold. Primarily, to develop the idea that energytransducing membrane systems normally contain a number of proteinaceous components whose role is to act co-operatively as conformationally switchable proton conductors, permitting fast, controlled lateral proton transfer along the surface of such energy-transducing membranes, and acting as the major energetic links between the various protonmotive sources and proton-accepting sinks embedded in such membranes. Secondly, to draw together evidence that the elements of such a protoneural network are themselves the prime target of the membrane-active colicins, and, thirdly, to point out that the recognition that such a network is an important feature of proton-coupled energy-transducing systems in vivo both provides a ready explanation for a variety of data apparently at odds with most presently accepted schemes of protonmotive energy transduction and renders intelligible a number of experimentally observable features of such systems for which a unifying view has not previously been offered. As will be clear from the following, we make no claim to the originality of many of the ideas presented here; we do believe, however, that our attempt to meld the conclusions drawn from a variety of experimental approaches into a unifying model will be helpful to those concerned with membrane energy transduction processes, their physiological roles and their molecular mechanisms. We begin with an outline summary of current ideas concerning the nature of energy transduction processes catalysed by membrane-located proteins.