A Biochemical Comparison of 6-Aminopenicillanic Acid,Benzylpenicillin,and 2,6-Dimethoxyphenylpenicillin

Abstract

Summary

Benzylpenicillin, 2,6-dimethoxyphenylpenicillin, and 6-aminopenicillanic acid were compared with respect to several biochemical activities. 2,6-Dimethoxy-phenylpenicillin and 6-aminopenicillanic acid were hydrolyzed at very low rates, compared to the rate for benzylpenicillin, by partially purified concentrated cell-free preparations of penicillinase derived from B. cereus, and at still lower rates by analogous preparations from S. aureus. For S. aureus, but not B. cereus, the growth-inhibitory concentrations of the two penicillinase-resistant compounds, particularly 2,6-dimethoxyphenylpenicillin, were much lower than that of benzylpenicillin. 2,6-Dimethoxyphenylpeni-cillin was a very effective inducer of penicillinase formation in B. cereus and in S. aureus. 6-Aminopenicillanic acid and benzylpenicillin were considerably less active as inducers of penicillinase in S. aureus than in B. cereus, as measured by effective inducing concentrations and by the amounts of enzyme formed. A mutant of a penicillinase-producing strain of S. aureus of increased resistance to 2,6-di-methoxyphenylpenicillin was obtained by successive subculture in increasing concentrations of the antibiotic. Its resistance did not appear to be due to the increased amount of its penicillinase content.

It is a pleasure to acknowledge the skillful assistance of Miss Emmy Lou Denny.

Addendum: Examination of the manometric assay of the rate of hydrolysis of 6-APA has revealed that this method yields artifactually low results with this particular compound because the product of enzymatic hydrolysis combines with some of the CO₂ liberated from the NaHCO₃ buffer system. Iodometric assay of this reaction shows the real rates of hydrolysis to be several-fold higher than given in Table I.