Review 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. Th