期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2004
卷号：101
期号：43
页码：15341-15345
DOI：10.1073/pnas.0406781101
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The structures of several powerful inhibitors of hydrolytic enzymes resemble that of the altered substrate in the transition state, except that a hydrogen atom replaces one substituent (typically the leaving group). To test the hypothesis that a water molecule might be present in the gap resulting from this replacement, we examined a transition-state analogue complex formed by Escherichia coli cytidine deaminase by Fourier transform ion cyclotron resonance MS in electrospray mode. Upon nebularization from aqueous solution under conditions (pH 5.6) where the enzyme is active, cytidine deaminase remains dimeric in the vapor phase. In the presence of inhibitor, the enzyme's exact mass can be used to infer the presence at each active site of zinc, 5-fluoro-3,4-dihydrouridine, and a single water molecule.
