Structure, function and regulation of primary H and Ca pumps

Pumps are proteins fuelled by cellular metabolites that transport solutes across biological membranes against their electrochemical gradients. Among the solutes handled by pumps, the active transport of protons (H + ) plays a pivotal role in the interconversion of biological energy forms such as chemical, osmotic and electrical energy. Thus, transport of H + is a fundamental cellular process. Most membranes in a living plant cell employ pumps to develop and maintain an unequal distribution of H + across the lipid bilayer. Although different families of H + pumps all transport the same ion, they have very different structures and mechanisms. Whereas H + pumps are the major focus of this review, other pumps in the plant, transporting cations such as Ca 2+ , will also be discussed so as to provide a general overview of pumps in a plant cell.