Plasma Membrane ATPase

Abstract

The existence of an ATP-driven proton pump in plant plasma membranes was suggested two decades ago from physiological studies on active transport (Poole 1978) and by measurement of electrical potentials (Spanswick 1981) across the plasma membrane of whole plant cells (Chap. 8). The pioneering work of Hodges et al. (1972) represented the first step toward the molecular characterization of this pump. These authors demonstrated the presence in partially purified plant plasma membranes of a K+-stimulated ATPase distinct from the mitochondrial and chloroplast ATPases. During the last decade the proton-pumping activity of this enzyme has been demonstrated in isolated plasma membrane vesicles (Sze 1985, see Chap. 7) and the ATPase has been partially purified and reconstituted in liposomes catalyzing ATP-driven proton transport (Serrano 1983). These studies also demonstrated similarities between ATPase enzymes from plant and fungal plasma membrane, which together constitute a novel group of ion-pumping ATPase (Serrano 1984a, 1985). Table 1 summarizes the properties of the two types of ion-pumping ATPases identified in biological membranes (Pedersen and Carafoli 1987a,b). The fungal and plant plasma membrane ATPases have the same structure and reaction mechanism as the other (E-P) ATPases involved in Na+, K+, and Ca2+ transport. On the other hand, they operate as electrogenic proton pumps, like most of the (F0F1) ATPases.