Variant of Penicillinase Mediated by an R Factor in Escherichia coli

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Abstract
The penicillinase from an Escherichia coli strain harboring an R factor R GN823 was purified and its properties were compared with those of a known type I penicillinase mediated by R factors. The molecular weight and S 20,w of the enzyme were 22,600 and 2.42 S , respectively. The isoelectric point of the enzyme was 6.9. These values are clearly different from those of type I penicillinase. The specific activity of the enzyme was 84,700 units per mg of the purified enzyme protein, which is about 20 times higher than that of the type I penicillinase. However, similarities were observed between the enzyme and the type I-penicillinase at optimal p H (6.5 to 7.0), optimal temperature (40 to 45C), substrate specificity, Michaelis constants for penicillins and cephaloridine, and effect of inhibitors. Furthermore, antiserum against type I penicillinase showed cross-reaction against this enzyme. The enzyme was named type Ib penicillinase, and the original type I penicillinase was renamed type Ia-penicillinase.