title: Covalent binding of moxalactam to cephalosporinase of Citrobacter freundii.
abstract: The inhibition of Citrobacter freundii cephalosporinase activity by moxalactam is shown to be due to the formation of a transiently stable covalent complex, probably acyl enzyme. The covalent complex formed was identified by coelution of [14C] moxalactam with the enzyme by using Sephadex G-25 gel filtration in the presence of 5.7 M guanidine hydrochloride and by analytical isoelectric focusing. Both the side-chain carboxyl group and the 7 alpha-methoxy group of moxalactam were necessary to stabilize the complex. Moxalactam is racemic with respect to the alpha carbon of the 7 beta-acylamino side chain, and the complex with the R epimer (half-life, 4.6 min) decomposed much more rapidly than that formed with the S epimer (half-life, 130 min). For other beta-lactam antibiotics that were stable to beta-lactamase, the half-lives of enzyme-antibiotic complexes were less than 4 min.
mesh_terms: D002510:Cephalosporinase / Q000302:isolation & purification / Q000378:metabolism*; D002850:Chromatography, Gel; D002954:Citrobacter / Q000201:enzymology*; D006207:Half-Life; D007525:Isoelectric Focusing; D007700:Kinetics; D009070:Moxalactam / Q000378:metabolism* / Q000494:pharmacology; D011485:Protein Binding; D013056:Spectrophotometry, Ultraviolet; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D065093:beta-Lactamase Inhibitors; D002510:Cephalosporinase; D001618:beta-Lactamases; D009070:Moxalactam