Bacterial three-subunit ureases assemble into a (UreABC)3 holoenzyme whose UreC subunit houses a dinuclear nickel metallocenter bridged by a carboxylated lysine residue, matured in vivo by the UreD, UreF, UreG, and UreE accessory proteins.
"The active site of urease contains two nickel atoms bridged by a carboxylated lysine and a solvent molecule, as shown for the K. aerogenes enzyme (Fig. 2).19 In addition, Ni1 is coordinated by two His residues plus a terminal water molecule while Ni2 is coordinated by two His, an Asp, and a terminal solvent."