Mono‐ and binuclear Zn‐β‐lactamase from Bacteroides fragilis: catalytic and structural roles of the zinc ions

Abstract
The Bacteroides fragilis Zn‐β‐lactamase is active with a mono‐ and a binuclear zinc site. The apoenzyme produced by removal of both Zn ions does not recover full activity upon readdition of Zn2+ in contrast to an active mono‐Zn form prepared at pH 6.0. Differences in k cat values observed are substrate‐dependent implying distinct mechanisms for the mono‐ and binuclear species. The substrate profile of a Zn,Cd hybrid obtained by selective exchange of one zinc ion is different from that of the Zn2 enzyme with a remarkable 15‐fold increased activity with cefoxitin as substrate.