Biochemical, Structural and Physiological Characteristics of Vacuolar H^+-Pyrophosphatase

Proton-translocating inorganic pyrophosphatase (H^+-PPase) actively translocates protons across membranes coupled with the hydrolysis of inorganic pyrophosphate (PPi). H^+-PPase, which is composed of a single protein and uses a simple compound as a substrate, has been recognized as a new type of ion pump in addition to the P-, F- and V-type ion-translocating ATPases. H^+- and Na^+-PPases are distributed in various organisms including plants, parasitic protozoa, Archaebacteria and bacteria, but are not present in animals or yeast. Vacuolar H^+-PPase has dual functions in plant cells: hydrolysis of cytosolic PPi to maintain the levels of PPi, and translocation of protons into vacuoles to maintain the acidity of the vacuolar lumen. Acidification performed with the vacuolar-type H^+-ATPase and H^+-PPase is essential to maintain acidic conditions, which are necessary for vacuolar hydrolytic enzymes and for supplying energy to secondary active transporters. Recent studies using loss-of-function mutant lines of H^+-PPase and complementation lines with soluble PPases have emphasized the physiological importance of the scavenging role of PPi. An overview of the main features of H^+-PPases present in the vacuolar membrane is provided in terms of tissue distribution in plants, intracellular localization, structure–function relationship, biochemical potential as a proton pump and functional stability.
ファイル公開日: 2019/07/01