DeGasperi R, al Daher S, Daniel P F, Winchester B G, Jeanloz R W, Warren C D
Carbohydrate Unit, Lovett Laboratories, Harvard Medical School, Charlestown, Massachusetts.
J Biol Chem. 1991 Sep 5;266(25):16556-63.
Lysosomal alpha-mannosidases were partially purified from bovine and feline liver and employed to digest a large number of oligosaccharides with structures corresponding to the oligomannosyl parts of complex, hybrid, and high-mannose glycans. The incubation products were identified by high pressure liquid chromatography with reference compounds of defined structure and by acetolysis. For all classes of substrates, the lysosomal alpha-mannosidases displayed a high degree of in vitro specificity with regard to the hydrolysis of mannose residues. Thus, in each case, 1 or at most 2 residues were always preferentially cleaved so that the degradative process proceeded down a well defined pathway. A comparison of the relative efficiency with which lysosomal alpha-mannosidases catalyzed the hydrolysis of particular oligosaccharides and of the structures of the resulting intermediates with those of the compounds accumulated in alpha-mannosidosis allows conclusions to be drawn regarding the nature of the enzymatic defect. In bovine alpha-mannosidosis, the oligosaccharides are those expected for a partial deficiency of normal lysosomal alpha-mannosidase, so that they correspond to intermediates in the normal catabolic pathway. In feline alpha-mannosidosis, in which the alpha-mannosidase deficiency is more severe than in cattle, the accumulated oligosaccharides primarily represent intact oligomannosyl moieties of N-linked glycans rather than the products of residual alpha-mannosidase activity.
溶酶体α-甘露糖苷酶从牛和猫的肝脏中部分纯化出来，并用于消化大量具有与复合聚糖、杂合聚糖和高甘露糖聚糖的寡甘露糖部分相对应结构的寡糖。通过高压液相色谱法，使用具有明确结构的参考化合物并通过乙酰解来鉴定孵育产物。对于所有类型的底物，溶酶体α-甘露糖苷酶在甘露糖残基水解方面表现出高度的体外特异性。因此，在每种情况下，总是优先切割1个或最多2个残基，使得降解过程沿着明确的途径进行。将溶酶体α-甘露糖苷酶催化特定寡糖水解的相对效率以及所得中间体的结构与α-甘露糖苷贮积症中积累的化合物的结构进行比较，可以得出关于酶缺陷性质的结论。在牛α-甘露糖苷贮积症中，寡糖是正常溶酶体α-甘露糖苷酶部分缺乏时预期的那些，因此它们对应于正常分解代谢途径中的中间体。在猫α-甘露糖苷贮积症中，α-甘露糖苷酶缺乏比牛更严重，积累的寡糖主要代表N-连接聚糖的完整寡甘露糖部分，而不是残留α-甘露糖苷酶活性的产物。
