<p>Microorganisms that can utilise halogenated compounds as growth substrates produce enzymes that cleave carbon-halogen bonds and are commonly called dehalogenases. The hydrolytic dehalogenases catalyse a nucleophilic displacement reaction, with water as the sole co-substrate [<cite idref="PUB00000125"/>]. They are divided into haloalkane dehalogenases and haloacid dehalogenases (HAD). HADs belong to a large superfamily of hydrolases with diverse substrate specificity, which also includes epoxide hydrolases, phosphoglycolate phosphatases, histidinol phosphate phosphatases, nitrophenyl phosphatases and numerous other proteins [<cite idref="PUB00003337"/>]. </p>This entry represents the pyrophosphatase PpaX subfamily of the HAD superfamily. These enzymes hydrolyse pyrophosphate formed during P-Ser-HPr dephosphorylation by HPrK/P [<cite idref="PUB00054962"/>]. They may play a role in controlling the intracellular pyrophosphate pool.