Abstract
An α-mannosidase capable of hydrolyzing three Man α1, 2-residues from pyridylamine (PA-) labeled Man9GlcNAc2 was purified from hen oviduct. The purity of the preparation was analyzed by PAGE; its molecular weight was 42, 000 by SDS-PAGE or 50, 000 by gel filtration. The pH optimum was 6.5. The enzyme was inactivated with EDTA; enzyme activity was restored by the addition of Ca2+. The enzyme acitivity was inhibited by 1-deoxymannojirimycin, but not by swainsonine. The substrate specificity of the purified enzyme was analyzed using PA-oligomannose-type sugar chains. When Man9GlcNAc2-PA was digested, Manα1-6 (Manαl-2Manαl-3) Manα1-6 (Manαl-3) Manβ1-4GlcNAcβ1-4Glc-NAc-PA was obtained as an end product, and the enzyme was incapable of hydrolyzing p-nitrophenyl α-D-mannoside and Man α1, 3- or Man α1, 6-residues. Judging from these characteristics, the enzyme was classified as a Man9-mannosidase or Golgi mannosidase I and speculated to participate in the processing or catabolism of glycoproteins.
