Maitra S K, Ballou C E
J Biol Chem. 1977 Apr 25;252(8):2459-69.
The 3-O-methyl-D-mannose-containing polysaccharide (MMP) from Mycobacterium smegmatis, first described by Gray and Ballou (Gray, G. R., and Ballou, C. E. (1971) J. Biol. Chem. 246, 6835-6842) is now shown to be a mixture of at least four isomers separable by gel filtration owing to differences in size and degree of methylation. The major component is 3-O-methylmannose but all contain small amounts of mannose. The molecular weights range from 2040 to 2490 and all are nonreducing. After Smith degradation, all yield a single large and one or more small fragments that give 3-O-methylmannose as the sole product of complete acid hydrolysis. The large Smith-degraded MMP components (SD-MMP) are similar to intact MMP and vary from 1830 to 2130 daltons, consistent with the loss of a single mannose; whereas the smaller fragments are the size of tri- to hexasaccharides and result from fragmentation of incompletely methylated chains. Controlled acid hydrolysis of [methyl-3H]MMP releases 6% of the methyl groups as [3H]methanol at a rate characteristic for the hydrolysis of methyl alpha-D-mannopyranoside. Proton magnetic resonance spectra of MMP and SD-MMP show a major methyl ether proton peak and a second small peak at higher field equivalent to about one methyl group per molecule. The results are consistent with the presence of an alpha-methyl aglycon at the reducing end of the chains. Methylation analysis of MMP isomers purified by high pressure liquid chromatography confirms that they are linear and unbranched. Methylation of [methyl-3H]MMP yields unlabeled tetra-O-methylmannose, showing that the chains are terminated by mannose. However, digestion of [methyl-3H]MMP with alpha-mannosidase releases mannose and exposes [methyl-3H]3-O-methylmannose. Smith degradation of [methyl-3H]MMP III yields a penta-to hexasaccharide product that can be resolved by high pressure liquid chromatography into two components. The distribution of radioactivity between these two fragments suggests that the chain was cleaved near the middle and that there must be an unmethylated mannose at that position. We conclude that the 3-O-methylmannose polysaccharides are linear unbranched chains of 11 to 14 sugar units, each terminated by a single mannose at the nonreducing end and by a methyl aglycon at the reducing end. Each isomer shows microheterogeneity, with 1 or 2 unmethylated mannose units near the middle of some but not all of the chains.
耻垢分枝杆菌中含3 - O - 甲基 - D - 甘露糖的多糖（MMP），最初由格雷和巴卢描述（格雷，G.R.，和巴卢，C.E.（1971年）《生物化学杂志》246，6835 - 6842），现在表明它是至少四种异构体的混合物，由于大小和甲基化程度的差异可通过凝胶过滤分离。主要成分是3 - O - 甲基甘露糖，但都含有少量甘露糖。分子量范围从2040到2490，且都是非还原性的。史密斯降解后，所有产物都产生一个大的片段和一个或多个小片段，完全酸水解的唯一产物是3 - O - 甲基甘露糖。大的史密斯降解的MMP成分（SD - MMP）与完整的MMP相似，分子量在1830到2130道尔顿之间，这与单个甘露糖的丢失一致；而较小的片段是三糖到六糖的大小，是不完全甲基化链断裂的结果。[甲基 - ³H]MMP的控制酸水解以α - D - 甘露吡喃糖苷水解的特征速率释放6%的甲基基团作为[³H]甲醇。MMP和SD - MMP的质子磁共振谱显示一个主要的甲基醚质子峰和在较高场强的第二个小峰，相当于每个分子约一个甲基。结果与链的还原端存在α - 甲基糖苷配基一致。通过高压液相色谱纯化的MMP异构体的甲基化分析证实它们是线性且无分支的。[甲基 - ³H]MMP甲基化产生未标记的四 - O - 甲基甘露糖，表明链以甘露糖结尾。然而，用α - 甘露糖苷酶消化[甲基 - ³H]MMP会释放甘露糖并暴露出[甲基 - ³H]3 - O - 甲基甘露糖。[甲基 - ³H]MMP III的史密斯降解产生一个五糖到六糖的产物，可通过高压液相色谱分离成两个成分。这两个片段之间的放射性分布表明链在中间附近被切割，并且在那个位置一定有一个未甲基化的甘露糖。我们得出结论，3 - O - 甲基甘露糖多糖是由11到14个糖单元组成的线性无分支链，每个链在非还原端由单个甘露糖终止，在还原端由甲基糖苷配基终止。每个异构体都表现出微不均一性，在一些但不是所有链的中间附近有1或2个未甲基化的甘露糖单元。
