Mechanistic Evaluation of <i>MelA</i> α-Galactosidase from <i>Citrobacter freundii</i>: A Family 4 Glycosyl Hydrolase in Which Oxidation Is Rate-Limiting
作者:Saswati Chakladar、Lydia Cheng、Mary Choi、James Liu、Andrew J. Bennet
DOI:10.1021/bi101808h
日期:2011.5.24
as mercaptoethanol. To delineate the mechanism of action for this GH4 enzyme, we measured leaving group effects, and the derived βlg values on V and V/K are indistinguishable from zero (−0.01 ± 0.02 and 0.02 ± 0.04, respectively). Deuterium kinetic isotope effects (KIEs) were measured for the weakly activated substrate phenyl α-d-galactopyranoside in which isotopic substitution was incorporated at C-1
来自弗氏柠檬酸杆菌的MelA基因已编码并在大肠杆菌中表达,该基因编码糖基水解酶家族4(GH4)α-半乳糖苷酶。重组酶通过氧化还原消除机制(包括C-3处的羟基氧化和C-1–C-2键之间的苯酚消除)来催化苯基α-半乳糖苷的水解,从而生成酶结合的糖中间体。为了获得最佳活性,MelA酶需要两个辅因子NAD +和Mn 2+,并需要添加还原剂(例如巯基乙醇)。划定此GH4酶作用的机制,我们测量的离去基团的效果,和所导出的β LG上的值V和V / K与零是无法区分的(分别为-0.01±0.02和0.02±0.04)。测量了弱活化的底物苯基α- d-吡喃半乳糖苷的氘动力学同位素效应(KIEs),其中同位素取代在C-1,C-2或C-3处并入。对于1-2 H,2- 2 H和3- 2 H同位素底物,分别在V上测得的KIE为1.06±0.07、0.91±0.04和1.02±0.06 。V / K上的对应值分别为1