Inorganic pyrophosphatase (EC: 3.6.1.1) (PPase) [PMID:2160278, PMID:1323891] is the enzyme responsible for the hydrolysis of pyrophosphate (PPi) which is formed principally as the product of the many biosynthetic reactions that utilize ATP. All known PPases require the presence of divalent metal cations, with magnesium conferring the highest activity. Among other residues, a lysine has been postulated to be part of or close to the active site. PPases have been sequenced from bacteria such as Escherichia coli (homohexamer), thermophilic bacteria PS-3 and Thermus thermophilus, from the archaebacteria Thermoplasma acidophilum, from fungi (homodimer), from a plant, and from bovine retina. In yeast, a mitochondrial isoform of PPase has been characterized which seems to be involved in energy production and whose activity is stimulated by uncouplers of ATP synthesis.

The sequences of PPases share some regions of similarities, among which is a region that contains three conserved aspartates that are involved in the binding of cations.