Both the mono- and di-anions of ellagic acid are effective inhibitors of the serine beta-lactamase CTX-M-15

Ellagic acid, a delta-lactone with ionisable phenolic residues, is an efficient time-dependent inhibitor of the serine beta-lactamase enzyme CTX-M-15. The pH-dependence of the rate of inhibition shows that both the mono- and di-anionic species of ellagic acid are effective inhibitors, both with second order rate constants of similar to 1.5 x 10(4) M-1 s(-1). The structurally similar delta-lactone urolithin A, which lacks the geometrically appropriate phenolic residue, shows only modest inhibitory activity against CTX-M-15. It is proposed that this inhibition by ellagic acid anions involves acylation of the active site serine and that the negative charge on the inhibitor is required for binding to the active site.