Kamisango K, Dell A, Ballou C E
J Biol Chem. 1987 Apr 5;262(10):4580-6.
From the 70% ethanol extract of Mycobacterium smegmatis cells, we isolated a mixture of weakly acidic oligosaccharides composed mainly of glucose and 6-O-methylglucose. The elution pattern from a Bio-Gel P-4 column suggested that the oligosaccharides were smaller than the O-methylglucose polysaccharide (MGP) and could be biosynthetic precursors. Analysis by fast-atom-bombardment mass spectrometry revealed that the oligosaccharides fit into a pattern for polysaccharide synthesis based on an alternate glucosylation-methylation mechanism until the chain reached the composition methylglucose11glucose5glyceric acid, at which time 2 glucose units are added to give glucose2methylglucose11glucose5glyceric acid. The addition of the last 2 glucoses and methylation of one of them to give mature MGP (methylglucose1glucose3methylglucose11glucose5glyceric acid) apparently occurs rapidly because the expected intermediates were not observed. Only 4 glucose units are present at the glyceric acid end of some molecules during all stages of the elongation process, and these represent precursors of a minor MGP homolog with an extra methyl group on the beta 1----3-linked glucose unit of MGP. alpha-D-Glucopyranosyl-(1----2)-D-glyceric acid and alpha-D-glucopyranosyl-(1----6)-alpha-D-glucopyranosyl-(1----2)-D-glycer ic acid were also isolated from the extract and correspond in structure to the expected initial precursors.
从耻垢分枝杆菌细胞的70%乙醇提取物中，我们分离出了一种主要由葡萄糖和6-O-甲基葡萄糖组成的弱酸性寡糖混合物。来自Bio-Gel P-4柱的洗脱模式表明，这些寡糖比O-甲基葡萄糖多糖（MGP）小，可能是生物合成前体。快速原子轰击质谱分析表明，这些寡糖符合基于交替糖基化-甲基化机制的多糖合成模式，直到链达到甲基葡萄糖11葡萄糖5甘油酸的组成，此时添加2个葡萄糖单元得到葡萄糖2甲基葡萄糖11葡萄糖5甘油酸。最后2个葡萄糖的添加以及其中一个的甲基化以产生成熟的MGP（甲基葡萄糖1葡萄糖3甲基葡萄糖11葡萄糖5甘油酸）显然迅速发生，因为未观察到预期的中间体。在延伸过程的所有阶段，一些分子的甘油酸末端仅存在4个葡萄糖单元，这些代表了一种次要MGP同系物的前体，该同系物在MGP的β1----3连接的葡萄糖单元上有一个额外的甲基。α-D-吡喃葡萄糖基-(1----2)-D-甘油酸和α-D-吡喃葡萄糖基-(1----6)-α-D-吡喃葡萄糖基-(1----2)-D-甘油酸也从提取物中分离出来，其结构与预期的初始前体一致。
