Inactivation of TEM-1 beta-lactamase by 6-acetylmethylenepenicillanic acid.

6-Acetylmethylenepenicillanic acid is a new kinetically irreversible inhibitor of various beta-lactamases. Interaction between 6-acetylmethylenepenicillanate and purified TEM-1 beta-lactamase during the inactivation process was investigated. 6-Acetylmethylenepenicillanate inhibited the enzyme in a second-order fashion with a rate constant of 0.61 microM-1 . S-1. The apparent inactivation constant decreased in the presence of increasing concentrations of the substrate benzylpenicillin. Native enzyme (pI 5.4) was converted into two inactive forms with pI 5.25 and 5.15, the latter form being transient and readily converted into the more stable form with pI 5.15. Even a 50-fold excess of inhibitor over enzyme did not produce any other inactivated species of the enzyme. All the results obtained suggest that 6-acetylmethylenepenicillanate is a potent irreversible and active-site-directed inhibitor of TEM-1 beta-lactamase.