ABSTRACT
The essential process of biological ATP synthesis is highly endergonic. Some ATP synthesis occurs by classical enzymological mechanisms in which an energy-releasing chemical transformation is strictly coupled to ADP phosphorylation within a single enzyme complex. This chapter reviews the current knowledge of structure of some of the enzymes that catalyse these ionmotive reactions and explores the types of mechanisms by which the coupling of electron transfer to ion translocation across a membrane can be achieved. In the discussions of coupling mechanisms, it describes how such local charge neutralization is likely to form a central feature of the coupling mechanism of several of the more complex ionmotive enzymes. The chapter discusses the protonmotive oxidases and the ion-coupled NADH dehydrogenases, enzymes in which the principle of electroneutrality by counterion uptake may provide a basis for understanding the more intricate coupling mechanisms that may be operative.
