Weisman L S, Ballou C E
J Biol Chem. 1984 Mar 25;259(6):3457-63.
The methylmannose polysaccharide, found in the cytoplasm of Mycobacterium smegmatis, is composed of 3-O-methylmannose units joined in alpha 1----4 linkage in a chain terminated by unmethylated mannose at the nonreducing end. An alpha 1----4-mannosyltransferase, one of the two enzymes involved in methylmannose polysaccharide elongation, has been identified in cell extracts. The activity is membrane-associated and catalyzes the transfer of mannose from GDP-mannose to oligomeric acceptors composed of 4 to 12 3-O-methylmannoses. 1H NMR spectroscopy and alpha-mannosidase digestion confirm that the mannose is attached by an alpha 1----4 linkage. In competition studies, the enzyme utilizes shorter oligomeric acceptors preferentially. The Km of the mannosyltransferase for MeMan4-OCH3 is 15-20 microM, for MeMan6-OCH3 it is 75-85 microM, and for GDP-mannose it is 55 microM.
在耻垢分枝杆菌细胞质中发现的甲基甘露糖多糖，由3 - O - 甲基甘露糖单元以α 1→4键连接而成，在非还原端由未甲基化的甘露糖终止形成一条链。α 1→4 - 甘露糖基转移酶是参与甲基甘露糖多糖延伸的两种酶之一，已在细胞提取物中被鉴定出来。该活性与膜相关，催化甘露糖从GDP - 甘露糖转移到由4至12个3 - O - 甲基甘露糖组成的寡聚受体上。1H核磁共振光谱和α - 甘露糖苷酶消化证实甘露糖通过α 1→4键连接。在竞争研究中，该酶优先利用较短的寡聚受体。甘露糖基转移酶对MeMan4 - OCH3的Km为15 - 20微摩尔，对MeMan6 - OCH3为75 - 85微摩尔，对GDP - 甘露糖为55微摩尔。
