Vacuolar H+-pyrophosphatase

The H+-translocating inorganic pyrophosphatase (H+-PPase) is a unique, electrogenic proton pump distributed among most land plants, but only some alga, protozoa, bacteria, and archaebacteria. This enzyme is a fine model for research on the coupling mechanism between the pyrophosphate hydrolysis and the active proton transport, since the enzyme consists of a single polypeptide with a calculated molecular mass of 71-80 kDa and its substrate is also simple. Cloning of the H+-PPase genes from several organisms has revealed the conserved regions that may be the catalytic site and/or participate in the enzymatic function. The primary sequences are reviewed with reference to biochemical properties of the enzyme, such as the requirement of Mg2+ and K+. In plant cells, H+-PPase coexists with H+-ATPase in a single vacuolar membrane. The physiological significance and the regulation of the gene expression of H+-PPase are also reviewed. (C) 2000 Elsevier Science B.V. All rights reserved.