Methodology for the Preparation of Pure Recombinant <i>S. cerevisiae</i> Lanosterol Synthase Using a Baculovirus Expression System. Evidence That Oxirane Cleavage and A-Ring Formation Are Concerted in the Biosynthesis of Lanosterol from 2,3-Oxidosqualene
作者:E. J. Corey、Hengmiao Cheng、C. Hunter Baker、Seiichi P. T. Matsuda、Ding Li、Xuelei Song
DOI:10.1021/ja963227w
日期:1997.2.1
The measured Vmax/KM ratios for 1, 3, and 4 were found to be 138, 9.4, and 21.9, respectively, a clear indication that oxirane cleavage and cyclization to form the A-ring are concerted, since the nucleophilicity of the proximate double bond influences the rate of oxirane cleavage. No catalytic metal ions could be detected in purified lanosterol synthase by atomic absorption analysis. Site-directed
羊毛甾醇合酶 [(S)-2,3-环氧角鲨烯变位酶(环化,羊毛甾醇形成),EC 5.4.99.7],来自酿酒酵母的酶,催化甾醇生物合成中复杂的环化/重排步骤,在杆状病毒感染的细胞中过表达并分三步纯化至均一。使用纯酶,使用 Michaelis-Menten 分析对 2,3-氧化角鲨烯 (1) 和其中 C-6 甲基被 H (3) 或 Cl (4) 替代的两种类似物进行环化动力学测定。测得的 1、3 和 4 的 Vmax/KM 比值分别为 138、9.4 和 21.9,这清楚地表明环氧乙烷裂解和环化形成 A 环是一致的,因为最接近的双环的亲核性键影响环氧乙烷裂解的速率。通过原子吸收分析,在纯化的羊毛甾醇合酶中没有检测到催化金属离子。六个高度保守的天冬氨酸残基(D → N 突变)中的每一个的定点诱变研究和...