来自大肠杆菌的tRNA-鸟嘌呤转糖基酶：乒乓动力学机制与亲核催化相一致。
tRNA-guanine transglycosylase from E. coli: a ping-pong kinetic mechanism is consistent with nucleophilic catalysis.
作者信息
Goodenough-Lashua DeeAnne M, Garcia George A
机构信息
Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, MI 48109-1065, USA.
出版信息
Bioorg Chem. 2003 Aug;31(4):331-44. doi: 10.1016/s0045-2068(03)00069-5.
tRNA-guanine transglycosylase (TGT) is a key enzyme in the post-transcriptional modification of certain tRNAs with the pyrrolopyrimidine base queuine. TGT is required for pathogenicity in Shigella flexneri, a human pathogen, and therefore is potentially a novel antibacterial target. Previous work has indicated that the TGT reaction proceeds through a covalent enzyme-tRNA complex [Biochemistry 40 (2001) 14123]. To further substantiate this mechanism, the determination of the kinetic mechanism for the TGT reaction was undertaken. Computational and graphical analyses of initial velocity data are most consistent with a ping-pong kinetic mechanism. The modes of inhibition of 7-methylguanine with respect to both guanine (competitive) and tRNA (uncompetitive) indicate that tRNA binds first to the enzyme. This kinetic mechanism is consistent with the covalent intermediate chemical mechanism and with our earlier study of a mechanism-based inhibitor [7-fluoromethyl-7-deazaguanine, Biochemistry 34 (1995) 15539] in which TGT inactivation was dependent upon the presence of tRNA.
转运RNA-鸟嘌呤转糖基酶（TGT）是某些转运RNA转录后修饰过程中，利用吡咯并嘧啶碱基 queuine 的关键酶。TGT 是人类病原菌福氏志贺氏菌致病性所必需的，因此它可能是一个新型抗菌靶点。先前的研究表明，TGT 反应通过共价酶-转运RNA复合物进行[《生物化学》40（2001）14123]。为了进一步证实这一机制，我们对 TGT 反应的动力学机制进行了测定。对初始速度数据的计算和图形分析与乒乓动力学机制最为一致。7-甲基鸟嘌呤对鸟嘌呤（竞争性）和转运RNA（非竞争性）的抑制模式表明，转运RNA首先与酶结合。这种动力学机制与共价中间体化学机制一致，也与我们早期对基于机制的抑制剂[7-氟甲基-7-脱氮鸟嘌呤，《生物化学》34（1995）15539]的研究一致，在该研究中，TGT失活依赖于转运RNA的存在。
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