Glycosidases of Aspergillus niger

Abstract A highly purified preparation of 1,2-α-mannosidase has been obtained from Aspergillus niger by using 2-O-α-d mannobiose as substrate. The disaccharide has been synthesized by the condensation of α-acetobromomannose with 1,3,4,6-tetra-O-acetyl-d-mannose followed by deacetylation of the resulting product. The enzyme shows a pH optimum of 4.8 and is stable in the pH range of 5.0 to 8.0. The Km and Vmax values for the enzyme are 2 mm and 1.3 µmoles per mg per min, respectively. The enzyme does not seem to be Zn++-dependent and is inhibited only weakly by d-mannono-(1→5)-lactone. The enzyme is highly specific for 1,2-α-d-mannosidic bonds and therefore readily hydrolyzes 2-O-α-mannobiose and 2-O-α-mannotriose. It does not hydrolyze 3-O-α-, 4-O-α-, and 6-O-α-mannobioses. The 2-acetamido-2-deoxy-3-O-α-, 4-O-α-, and 6-O-α-d-mannopyranosyl-d-glucoses are also not hydrolyzed. It does not release mannose from yeast mannan, ovalbumin, β-galactosidase-β-N-acetyl-glucosaminidase-treated desialyzed human chorionic gonadotropin, α1 acid glycoprotein, and fetuin.