The beta-lactamase of Streptomyces cacaoi: interaction with cefoxitin and beta-iodopenicillanate

Cefoxitin was a very poor substrate for the beta-lactamase of Streptomyces cacaoi (kcat = 2.7 x 10(-4) s-1). In the presence of nitrocefin, a good substrate, cefoxitin behaved as a transient inactivator by immobilizing a large proportion of the enzyme as the acyl enzyme intermediate. The enzyme was also inactivated by beta-iodopenicillanate. In this case, the acyl enzyme rearranged into an alpha-beta unsaturated ester and inactivation was irreversible. In contrast to the situation prevailing with the Streptomyces albus G beta-lactamase, no turn-over of beta-iodopenicillanate was observed.