title: A thiono-beta-lactam substrate for the beta-lactamase II of Bacillus cereus. Evidence for direct interaction between the essential metal ion and substrate.
abstract: An 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.
authors.affiliation: Department of Chemistry, Wesleyan University, Middletown, CT 06457.
authors.forename: B P
authors.initials: BP
authors.lastname: Murphy
authors.forename: R F
authors.initials: RF
authors.lastname: Pratt
mesh_terms: D001409:Bacillus cereus / Q000201:enzymology*; D001665:Binding Sites; D002104:Cadmium / Q000378:metabolism; D002510:Cephalosporinase / Q000378:metabolism*; D002511:Cephalosporins / Q000378:metabolism*; D003035:Cobalt / Q000378:metabolism; D007700:Kinetics; D008345:Manganese / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism; D015032:Zinc / Q000378:metabolism; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D002511:Cephalosporins; D013438:Sulfhydryl Compounds; D002104:Cadmium; D003035:Cobalt; D008345:Manganese; D002510:Cephalosporinase; D001618:beta-Lactamases; D015032:Zinc