Proton pumping pyrophosphatase

Two types of inorganic diphosphatase, very different in terms of both amino acid sequence and structure, have been characterised to date: soluble and transmembrane proton-pumping pyrophosphatases (sPPases and H(⁺)-PPases, respectively). sPPases are ubiquitous proteins that hydrolyse pyrophosphate to release heat, whereas H⁺-PPases, so far unidentified in animal and fungal cells, couple the energy of PPi hydrolysis to proton movement across biological membranes. The latter type is represented by this group of proteins. H⁺-PPases are also called vacuolar-type inorganic pyrophosphatases (V-PPase) or pyrophosphate-energised vacuolar membrane proton pumps. In plants, vacuoles contain two enzymes for acidifying the interior of the vacuole, the V-ATPase and the V-PPase (V is for vacuolar).

Two distinct biochemical subclasses of H⁺-PPases have been characterised to date: K⁺-stimulated and K⁺-insensitive.