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外文期刊>The biochemical journal
>A thiono-β-lactam substrate for the β-lactamase II of Bacillus cereus. Evidence for direct interaction between the essential metal ion and substrate
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A thiono-β-lactam substrate for the β-lactamase II of Bacillus cereus. Evidence for direct interaction between the essential metal ion and substrate
pAn 8-thionocephalosporin was shown to be a substrate of the beta-lactamase II of Bacillus cereus, a zinc metalloenzyme. Although it is a poorer substrate, as judged by the Kcat./Km parameter, than the corresponding 8-oxocephalosporin, the discrimination against sulphur decreased when the bivalent metal ion in the enzyme active site was varied in the order Mn2+ (the manganese enzyme catalysed the hydrolysis of the oxo compound but not that of the thiono compound), Zn2+, Co2+ and Cd2+. This result is taken as evidence for kinetically significant direct contact between the active-site metal ion of beta-lactamase II and the beta-lactam carbonyl heteroatom. No evidence was obtained, however, for accumulation of an intermediate with such co-ordination present./p
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