title: Substitution of aspartic acid-217 of Citrobacter freundii cephalosporinase and properties of the mutant enzymes.
abstract: On the assumption that Asp-217 of a Citrobacter freundii cephalosporinase forms a salt-bridge with the conserved Lys-67, Asp-217 was changed to glutamic acid, threonine or lysine. The mutant enzymes retained about the same level of activity as that of the wild-type enzyme, and the participation of Asp-217 in the salt-bridge was ruled out. However, the mutations resulted in an increase in hydrolytic activity toward oxyimino-cephalosporins such as cefuroxime, cefmenoxime and ceftazidime, suggesting a possible mechanism of the bacterial resistance to the novel beta-lactams by a single mutation in cephalosporinases.
authors.affiliation: Division of Microbial Chemistry, Faculty of Pharmaceutical Sciences, Chiba University, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Tsukamoto
authors.forename: R
authors.initials: R
authors.lastname: Kikura
authors.forename: R
authors.initials: R
authors.lastname: Ohno
authors.forename: T
authors.initials: T
authors.lastname: Sawai
mesh_terms: D001224:Aspartic Acid; D002510:Cephalosporinase / Q000235:genetics* / Q000378:metabolism; D002954:Citrobacter / Q000201:enzymology* / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005971:Glutamates; D018698:Glutamic Acid; D007700:Kinetics; D008239:Lysine; D009154:Mutation; D013379:Substrate Specificity; D013912:Threonine; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D005971:Glutamates; D013912:Threonine; D001224:Aspartic Acid; D018698:Glutamic Acid; D002510:Cephalosporinase; D001618:beta-Lactamases; D008239:Lysine