Murakami K, Yoshida T
Antimicrob Agents Chemother. 1985 May;27(5):727-32. doi: 10.1128/AAC.27.5.727.
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.
羟羧氧酰胺菌素对弗氏柠檬酸杆菌头孢菌素酶活性的抑制作用表明是由于形成了一种暂时稳定的共价复合物，可能是酰基酶。通过在5.7M盐酸胍存在下使用Sephadex G-25凝胶过滤以及分析等电聚焦，将形成的共价复合物与酶共同洗脱来鉴定[14C]羟羧氧酰胺菌素。羟羧氧酰胺菌素的侧链羧基和7α-甲氧基对于稳定复合物都是必需的。羟羧氧酰胺菌素在7β-酰基氨基侧链的α碳方面是外消旋的，与R型差向异构体形成的复合物（半衰期为4.6分钟）比与S型差向异构体形成的复合物（半衰期为130分钟）分解得快得多。对于对β-内酰胺酶稳定的其他β-内酰胺抗生素，酶-抗生素复合物的半衰期小于4分钟。
