Inactivation of β-lactamases from Enterobacter cloacae by monophosphams

Amongst the monocyclic β-lactam antibiotics, selected monophosphams were potent mechanism-based inactivators of the P99 and E2 cephalosporinases of Enterobacter cloacae. Inhibition of these enzymes was time-dependent with second order rate constants for inactivation of 100,000 to 20,000,000 1/mole/min. After incubation for 24 h at least 99% of the enzymatic activity was inhibited when enzyme was exposed to a ten-fold excess of inactivator. Amongst the monophosphams three classes of inhibitors were seen: irreversible inactivators as described above, transient inactivators and competitive (inhibitory) substrates.