Coherent Properties of Energy-Coupling Membrane Systems

Abstract

An understanding of the organization of biological systems is predicated upon an understanding of their energetics. Thus the present chapter will give a very broad overview of some of the current thinking in bioenergetics, with especial reference to the formation of ATP linked to the transport of electrons down their electrochemical potential gradient, as catalyzed by biomembranes containing mobile protein complexes participating in the two half-reactions (Fig. 1). Here we see how the downhill reactions of electron transport are coupled to the otherwise endergonic ATP synthase reaction through the transfer of one or more quanta of free energy (Fig. 1 A). Arguably, the major problem of bioenergetics concerns the nature of this free-energy-transducing quantum, and Fig. IB shows some of the salient possibilities under discussion (Kell and Harris 1985a). Only the celebrated chemiosmotic model may be regarded as reasonably well developed (Nicholls 1982; Harold 1986), but since its perceived shortcomings have been discussed elsewhere in extenso (e.g. Ferguson and Sorgato 1982; Kell 1979, 1986a, 1987a, 1988; Ferguson 1985; Kell and Hitchens 1983; Westerhoff et al. 1984a; Kell and Westerhoff 1985), I shall not concentrate on it in detail here, where a more heuristic overview is appropriate.