Binds 2 Zn(2+) ions per subunit. Expression is under strict control of the medium composition. Induced by citrate, probably via the two-component regulatory system CitT/CitS. Repressed by rapidly metabolized carbon sources like glucose, glycerol and inositol, via the carbon catabolite repression system. Is also repressed by succinate and glutamate, albeit to a lesser extent. Belongs to the metallo-beta-lactamase superfamily.