Iodometric Assay of Penicillinase

Abstract

THE series of iodometric methods¹ for assaying penicillinase reported here permits enzyme activity to be measured easily over wide ranges of pH and temperature, with higher speed, accuracy or sensitivity than were previously attainable². Although designed for the penicillinase of B. cereus NRRL-569, it appears likely that they may be equally suitable in principle for penicillinase from other sources. ‘Unit rate of penicillin destruction’ is used here to mean a destruction-rate of 1 µmol./hr. Since the amount of a penicillinase which will give unit rate of destruction depends on the nature of the enzyme and the conditions to which it is exposed, a ‘unit dose’ (U.D.) of B. cereus NRRL-569 penicillinase is here defined as that amount of the enzyme which gives unit rate of destruction when exposed to 0.005 M sodium benzyl penicillin in 0.2 M potassium phosphate buffer at pH 6.5 and 30° C. The commercial crystalline sodium penicillin G of Glaxo, Ltd., is used in the following assays; its potency is stated to be 1,650 I.U./mgm.