In vitro inhibition of urokinase by penicillins

Urokinase activity was assayed by a two-stage globinolytic method and by a direct chromogenic assay. With both methods, the enzyme activity was found to be inhibited by penicillins. The inhibition by penicillin G, carbenicillin, cloxacillin and penicilloic acid was dose-dependent. The Ki of penicillin G and urokinase with the S-2444 as substrate is 4 mM. This compound exhibited a competitive pattern of inhibition. Ampicillin and 6-amino penicillanic acid failed to inhibit urokinase. These results imply that hydrophobic side chains of penicillins interact with the active site of urokinase. The present observation could be relevant in clinical situation in which high doses of beta-lactam antibiotics could modulate the endogenous fibrinolytic activity of circulating urokinase.