Kumano M, Omichi K, Hase S
Department of Chemistry, Osaka University College of Science.
J Biochem. 1996 May;119(5):991-7. doi: 10.1093/oxfordjournals.jbchem.a021340.
A cytosolic neutral alpha-mannosidase was purified from bovine liver. Its molecular weight was found to be 500,000 on gel filtration. The activity of the enzyme toward Man alpha 1-6-(Man alpha 1-3)Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc-PA was increased 26-fold by preincubation with 1 mM Co2+. Man alpha 1-6(Man alpha 1-3)Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc was hydrolyzed by the enzyme to Man alpha 1-3Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc, which was further hydrolyzed to Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc. The rate of hydrolysis was 15-fold greater than that of Man alpha 1-6(Man alpha 1-3)Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc beta 1-4GlcNAc. This substrate specificity suggested that the enzyme could be involved in the degradation of oligomannose-type sugar chains with one GlcNAc residue released from glycoproteins by endo-beta-N-acetylglucosaminidase, and supported a pathway for glycoprotein catabolism via oligomannosyl glycans with one GlcNAc residue proposed on the basis of an earlier study on a cytosolic neutral alpha-mannosidase from Japanese quail oviduct [Oku, H. and Hase, S. (1991) J. Biochem. 110, 982-989].
从牛肝脏中纯化出一种胞质中性α-甘露糖苷酶。通过凝胶过滤法测得其分子量为500,000。该酶对Manα1-6-(Manα1-3)Manα1-6(Manα1-3)Manβ1-4GlcNAc-PA的活性在与1 mM Co2+预孵育后增加了26倍。Manα1-6(Manα1-3)Manα1-6(Manα1-3)Manβ1-4GlcNAc被该酶水解为Manα1-3Manα1-6(Manα1-3)Manβ1-4GlcNAc，后者进一步水解为Manα1-6(Manα1-3)Manβ1-4GlcNAc。其水解速率比Manα1-6(Manα1-3)Manα1-6(Manα1-3)Manβ1-4GlcNAcβ1-4GlcNAc的水解速率高15倍。这种底物特异性表明该酶可能参与了寡甘露糖型糖链的降解，这些糖链是由内切β-N-乙酰葡糖胺酶从糖蛋白释放出一个GlcNAc残基后形成的，这支持了基于早期对日本鹌鹑输卵管胞质中性α-甘露糖苷酶的研究提出的通过带有一个GlcNAc残基的寡甘露糖基聚糖进行糖蛋白分解代谢的途径[Oku, H.和Hase, S. (1991) J. Biochem. 110, 982 - 989]。
