Structure and regulation of insect plasma membrane H⁺ V-ATPase

H⁺V-ATPases (V-ATPases) are found in two principal locations, in endomembranes and in plasma membranes. The plasma membrane V-ATPase from the midgut of larval Manduca sexta is the sole energizer of all transepithelial secondary transport processes. At least two properties make the lepidopteran midgut a model tissue for studies of general aspects of V-ATPases. First, it is a rich source for purification of the enzyme and therefore for structural studies: 20 larvae provide up to 0.5 mg of holoenzyme, and soluble, cytosolic V₁ complexes can be obtained in even greater amounts of up to 2mg. Second, midgut ion-transport processes are strictly controlled by the regulation of the V-ATPase, which is the sole energizer of all ion transport in this epithelium. Recent advances in our understanding the structure of the V₁ and V(o) complexes and of the regulation of the enzyme's biosynthesis and ion-transport activity will be discussed.