few have been studied in vitro. GenK is one such enzyme that catalyzes methylation of the 6′-carbon of gentamicin X2 (GenX2) to produce G418 during the biosynthesis of gentamicins. Reported herein, several alternative substrates and fluorinated substrate analogs were prepared to investigate the mechanism of methyl transfer from Cbl to the substrate as well as the substrate specificity of GenK. Experiments
已经通过序列比对和/或遗传分析鉴定了许多依赖
钴胺素(Cbl)的自由基S-
腺苷-1-甲
硫氨酸(S
AM)甲基转移酶。但是,很少有体外研究。GenK是一种这样的酶,其在
庆大霉素的
生物合成期间催化
庆大霉素X 2(GenX 2)的6'-碳的甲基化以产生G418。本文报道,制备了几种替代的底物和
氟化的底物类似物以研究甲基从Cbl转移到底物的机理以及GenK的底物特异性。此处还显示了具有
氘代底物的实验,以证明6'- pro - RGenX 2的-氢原子被5'-dAdo·自由基立体选择性地提取出来,并且甲基化发生并保留了C6'处的构型。基于这些观察结果,提出了GenK催化模型,其中防止了带有自由基的碳的自由旋转,并且自由基S
AM机制相对于酶活性位点中的底物与Me-Cbl辅因子相邻而不是相反。