Kinetics of <i>β</i>–Lactamase Inactivation of Penicillins

Abstract

Experiments were conducted that showed Staphylococcusaureusβ-lactamase activity to be inhibited the most by dicloxacillin, cephaloglycin, and 7-ACA, to a lesser degree by cloxacillin, quinacillin, oxacillin, 6-APA, cephalexin, nafcillin, and ancillin and least of all by methicillin. Bacillus cereus β-lactamase activity was inhibited most by nafcillin and dicloxicillin and only moderately by all the other inhibitors cited, including methicillin, which was least effective. The degree of inhibition was shown to depend on the structural characteristics of the inhibitor, the time of exposure of enzyme to inhibitor, and the ratio of amount of inhibitor to amount of substrate. The inhibition was of the competitive type. The compounds having the highest affinity for the enzyme or the lowest K_i value were the strongest inhibitors and were most effective in protecting the susceptible substrate from hydrolysis.

Inactivation of Bacillus cereusβ‐Lactamase by Halogenated Isoxazolylpenicillins

“…The data reported in the present work differ somewhat from the results obtained by Hou and Poole [5] : according to these authors, dicloxacillin (as well as other fl-lactamase-resistant penicillins) causes an inactivation of both Staphylococcus aureus and B. cereus enzymes, the inactivation occurring, however, even at 25 "C and giving a pattern described by the authors as 'competitive' type inhibition (i.e. with a constancy of k t 2 and a decrease of On the other hand, the authors claim that dicloxacillin does not act as a competitive inhibitor when added together with the substrate.…”

Accumulation of acyl-enzyme intermediates during turnover of penicillins by the class A β-lactamase of Staphylococcus aureus PC1

“…Dansylpenicillin appeared to be a normal penicillin substrate of the PCI -lactamase. There was no sign, for example, of A-type substrate [18] behaviour, which has been seen in the interactions of this enzyme with a variety of penicillinase-resistant penicillins [19][20][21][22][23][24][25]. Steadystate kinetic parameters (kcat = 75 + 4 s-1 and Km = 3.0+0.7,UM at pH 7.5, and kcat = 7.4+ 1.0 s-and Km = 6.9 + 2.4 /uM at pH 9.0) were similar to those of benzylpenicillin [7].…”

Association of Halogenated Isoxazolylpenicillins with Penicillinase-Sensitive <i>β</i>-Lactam Antibiotics

“…Using cephaloridine as substrate for the assay of enzyme activity [1,3], the equilibrium constant for inactivation at 37 °C, Kinact, was 69 /¿M with dicloxacillin and 32 ¡XM . with flucloxacillin, as compared to values of 350 and 240 /uM, respectively, for the inhibition constants K/s.…”