Microiodometric determination of beta-lactamase activity.

The product of beta-lactamase activity (a penicilloic acid in the case of a penicillin) is stoichiometrically oxidized by iodine. Hence, the beta-lactamase activity can be measured as decolorization of the blue starch-iodine complex. Since the decolorization is a slow process, the rate of decolorization gave an underestimate of the rate of penicillin hydrolysis until a steady state was obtained after 15 to 20 min. If the reaction mixture (3 ml) contained no more than 0.001 unit of enzyme, a correct determination of beta-lactamase activity was obtained from the microiodometric method described. The method is sensitive and some applications are mentioned.