[6][7] 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.

[12] Though the precise mechanism of catalysis via inorganic pyrophosphatase in most organisms remains uncertain, site-directed mutagenesis studies in Escherichia coli have allowed for analysis of the enzyme active site and identification of key amino acids.

Direct coordination with these four magnesium ions and hydrogen bonding interactions with Arg43, Lys29, and Lys142 (all positively charged residues) have been shown to anchor the substrate to the active site.

By promoting the rapid hydrolysis of pyrophosphate (PPi), Inorganic pyrophosphatase provides the driving force for the activation of fatty acids destined for beta oxidation.

Examination of prokaryotic and eukaryotic forms of soluble inorganic pyrophosphatase (sPPase, Pfam PF00719) has shown that they differ significantly in both amino acid sequence, number of residues, and oligomeric organization.