Sterol C -methyl transferase from Prototheca wickerhamii mechanism, sterol specificity and inhibition
作者:Anil T Mangla、W.David Nes
DOI:10.1016/s0968-0896(00)00040-7
日期:2000.5
C24, C23 or C22 are particularly potent non-competitive inhibitors (Ki for the most potent inhibitor tested, 25-azacycloartanol, was ca. 2 nM, four orders of magnitude less than the Km for cycloartenol of 28 microM), supporting the intermediacy of the 24-methyl C24(25)-carbenium ion intermediate. Ergosterol, but neither cholesterol nor sitosterol, was found to inhibit SMT activity (Ki = 80 microM). The
发现来自Prototheca wickerhamii(一种非光合酵母样藻类)的膜结合固醇甲基转移酶(SMT)酶将适当的delta24(25)-甾醇受体分子C-甲基化为delta25(27)-24beta-甲基产品立体选择性地。与底物对一起孵育-[2H3-甲基] AdoMet和环戊烯醇,以及AdoMet和[27-(13)C]羊毛甾醇-随后通过同位素标记产品的1H和13C NMR分析,显示了si-face(beta-面部攻击)的C-甲基化机制和羊毛甾醇上的Pro-Z甲基(C27)形成delta25(27)-双键的区域特异性。该酶对具有3β-羟基,平面原子核和侧链的甾醇具有底物偏爱,该甾醇定向为天然底物环戊烯醇的“右手”结构(20R手性)特征。通过Superose 6 FPLC测定,SMT的表观天然分子量约为154,000。含有取代C24和C25或相关结构修饰的杂原子的一系列固醇类似物,包括甾体