<p>Urease (urea amidohydrolase, <db_xref db="EC" dbkey="3.5.1.5"/>) catalyses the hydrolysis of urea to form ammonia and carbamate. The subunit composition of urease from different sources varies [<cite idref="PUB00010725"/>], but each holoenzyme consists of four structural domains [<cite idref="PUB00005206"/>]: three structural domains and a nickel-binding catalytic domain common to amidohydrolases [<cite idref="PUB00004994"/>]. Urease is unique among nickel metalloenzymes in that it catalyses a hydrolysis rather than a redox reaction. In <taxon tax_id="210">Helicobacter pylori</taxon>, the gamma and beta domains are fused and called the alpha subunit (<db_xref db="INTERPRO" dbkey="IPR008223"/>). The catalytic subunit (called beta or B) has the same organisation as the Klebsiella alpha subunit. Jack bean (<taxon tax_id="3823">Canavalia ensiformis</taxon>) urease has a fused gamma-beta-alpha organisation (<db_xref db="INTERPRO" dbkey="IPR008221"/>).</p> <p> The N-terminal domain is a composite domain and plays a major trimer stabilising role by contacting the catalytic domain of the symmetry related alpha-subunit [<cite idref="PUB00005206"/>]. </p>