Interaction of Staphylococcal Penicillinase and 6-[D(-

Citri and Zyk (3) recently showed that the penicillinase of Bacillus cereus, on interaction with substrates, may yield conformational changes at the active site of the enzyme. Earlier studies by a number of investigators (1, 2, 4, 6, 8, 11) showed that penicillin analogues resistant to staphylococcal penicillinase, such as methicillin, may cause inactivation ofthe enzyme. In contrast, Richmond (10), working with purified penicillinase, found that methicillin did not affect the enzyme. Hamilton-Miller and Smith (7) found that methicillin did not inhibit staphylococcal penicillinase but did inhibit penicillinase from B. cereus. These investigators, after working with a number of penicillinases, concluded that the state of purity of the enzymes, the source of the enzyme, and the type of penicillinase (whether it was cellbound) were factors that influenced the ability of resistant penicillins to inhibit the enzyme. This report describes the interaction of a-guanidino penicillin and staphylococcal penicillinase, in which both hydrolysis of the compound and inactivation of the enzyme occur. a-Guanidino penicillin, 6-[D(-)-a-guanidino-phenylacetamido]-penicillanic acid, is one of the compounds from a new class of penicillins described by Leanza et al. (9).