Article (Scientific journals)
The mechanism of catalysis and the inhibition of the Bacillus cereus zinc-dependent beta-lactamase.
Bounaga, S.; Laws, A. P.; Galleni, Moreno et al.
1998In Biochemical Journal, 331 ( Pt 3), p. 703-11
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Keywords :
Acetamides/pharmacology; Acetanilides; Bacillus cereus/enzymology; Binding Sites/physiology; Catalysis; Cephaloridine/metabolism; Hydrogen-Ion Concentration; Kinetics; Methanol/pharmacology; Molecular Structure; Osmolar Concentration; Penicillin G/metabolism; Sulfhydryl Compounds/pharmacology; Zinc/pharmacology; beta-Lactamase Inhibitors; beta-Lactamases/metabolism
Abstract :
[en] The plot of kcat/Km against pH for the Bacillus cereus 569/H beta-lactamase class B catalysed hydrolysis of benzylpenicillin and cephalosporin indicates that there are three catalytically important groups, two of pKa 5.6+/-0.2 and one of pKa 9.5+/-0.2. Below pH 5 there is an inverse second-order dependence of reactivity upon hydrogen ion concentration, indicative of the requirement of two basic residues for catalysis. These are assigned to zinc(II)-bound water and Asp-90, both with a pKa of 5.6+/-0.2. A thiol, N-(2'-mercaptoethyl)-2-phenylacetamide, is an inhibitor of the class B enzyme with a Ki of 70 microM. The pH-dependence of Ki shows similar pH inflections to those observed in the catalysed hydrolysis of substrates. The pH-independence of Ki between pH 6 and 9 indicates that the pKa of zinc(II)-bound water must be 5.6 and not the higher pKa of 9.5. The kinetic solvent isotope effect on kcat/Km is 1.3+/-0.5 and that on kcat is 1.5. There is no effect on reactivity by either added zinc(II) or methanol. The possible mechanisms of action for the class B beta-lactamase are discussed, and it is concluded that zinc(II) acts as a Lewis acid to stabilize the dianionic form of the tetrahedral intermediate and to provide a hydroxide-ion bound nucleophile, whereas the carboxylate anion of Asp-90 acts as a general base to form the dianion and also, presumably, as a general acid catalyst facilitating C-N bond fission.
Disciplines :
Biochemistry, biophysics & molecular biology
Author, co-author :
Bounaga, S.
Laws, A. P.
Galleni, Moreno ;  Université de Liège - ULiège
Page, M. I.
Language :
English
Title :
The mechanism of catalysis and the inhibition of the Bacillus cereus zinc-dependent beta-lactamase.
Publication date :
1998
Journal title :
Biochemical Journal
ISSN :
0264-6021
eISSN :
1470-8728
Publisher :
Portland Press, United Kingdom
Volume :
331 ( Pt 3)
Pages :
703-11
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 01 December 2015

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