Eneyskaya E V, Kulminskaya A A, Savel'ev A N, Shabalin K A, Golubev A M, Neustroev K N
Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg, 188350, Russia.
Biochem Biophys Res Commun. 1998 Apr 7;245(1):43-9. doi: 10.1006/bbrc.1998.8382.
The 160 kDa alpha-mannosidase (E.C. 3.2.1.24) isolated from culture filtrate of Trichoderma reesei has wide aglycon specificity but cleaves the alpha1 --> 2 and alpha1 --> 3 mannosidic bonds with higher rate than alpha1 --> 6 bond and slowly hydrolyses yeast mannan and 1,6-alpha-mannan. The specific activity of the enzyme and rate constant in the reaction with p-nitrophenyl-alpha-D-mannopyranoside were 0.15 U/mg and 1.62 x 10(-4) microM/min/microg, respectively, at optimal pH 6.5. We have found that in vitro enzyme is able to cleave off 30% of total alpha-mannopyranosyl residues from N- and O-linked glycans of secreted glycoproteins. The activity of the alpha-mannosidase toward glycoproteins in vivo was studied comparing the structures of O- and N-linked glycans of glycoproteins isolated from the cultures growing with and without 1-deoxymannojirimycin, an inhibitor of alpha-mannosidases. Difference in structures of these glycans may be explained by postsecretory deglycosylation catalysed by the alpha-mannosidase.
从里氏木霉培养滤液中分离出的160 kDa α-甘露糖苷酶（E.C. 3.2.1.24）具有广泛的苷元特异性，但切割α1→2和α1→3甘露糖苷键的速率高于α1→6键，且缓慢水解酵母甘露聚糖和1,6-α-甘露聚糖。在最佳pH 6.5条件下，该酶与对硝基苯基-α-D-甘露吡喃糖苷反应的比活性和速率常数分别为0.15 U/mg和1.62×10⁻⁴ μM/min/μg。我们发现，体外该酶能够从分泌糖蛋白的N-和O-连接聚糖中切割掉30%的总α-甘露吡喃糖基残基。通过比较在添加和不添加α-甘露糖苷酶抑制剂1-脱氧甘露基野尻霉素的情况下培养所得糖蛋白的O-和N-连接聚糖结构，研究了α-甘露糖苷酶在体内对糖蛋白的活性。这些聚糖结构的差异可能是由α-甘露糖苷酶催化的分泌后去糖基化作用所致。
