Ammonia produced by ureolysis increases the gastric pH thereby providing an environment permissive for colonization of the stomach. 2 H(+) + H2O + urea = CO2 + 2 NH4(+) Binds 2 nickel ions per subunit. Nitrogen metabolism; urea degradation; CO(2) and NH(3) from urea (urease route): step 1/1. Heterohexamer of 3 UreA (alpha) and 3 UreB (beta) subunits. Four heterohexamers assemble to form a 16 nm dodecameric complex (By similarity). Also associates with the outer membrane upon autolysis of neighboring bacteria. Carboxylation allows a single lysine to coordinate two nickel ions. The novel dodecameric structure of the enzyme may allow it to remain active at the cell surface at acidic gastric pH. Within this dodecameric structure the 12 active sites are clustered within the interior of the proteinaceous shell. This may allow a high local concentration of ammonia within the enzyme which may protect the nickel-chelating groups from protonation (By similarity). Belongs to the metallo-dependent hydrolases superfamily. Urease alpha subunit family. The orthologous protein is known as the alpha subunit (UreC) in most other bacteria.