The β-Lactamase ofStreptomyces Cacaoi: Interaction with Cefoxitin and β-Iodopenicillanate

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Abstract
Cefoxitin was a very poor substrate for the β-lactamase of Streptomyces cacaoi (kcat = 2.7 × 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 β-iodopenicillanate. In this case, the acyl enzyme rearranged into an α-β unsaturated ester and inactivation was irreversible. In contrast to the situation prevailing with the Streptomyces albus G β-lactamase, no turn-over of β-iodopenicillanate was observed.