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. Heterotrimer of UreA (gamma), UreB (beta) and UreC (alpha) subunits. Three heterotrimers associate to form the active enzyme. Carboxylation allows a single lysine to coordinate two nickel ions. Belongs to the metallo-dependent hydrolases superfamily. Urease alpha subunit family. Neither O157 strain expresses urease due to a truncation of ureD, the last gene of the probable operon. Urease activity is restored in O157 / Sakai upon complementation with wild-type ureD. This region of the chromosome is duplicated in strain O157:H7 / EDL933 but not in O157:H7 / Sakai.