PROPERTIES OF A BETA-D-MANNOSIDASE FROM ASPERGILLUS-NIGER

The β-d-mannosidase (β-d-mannoside mannohydrolase, EC 3.2.1.25) from culture filtrate of Aspergillus niger has been purified in large amounts by fractionation with (NH4)2SO4 and DEAE-cellulose chromatography. The removal of traces of α-d-galactosidase was performed on a Sepharose-ε{lunate}-aminocaproylgalactosylamine column. The final enzyme preparation (specific activity 188 units) has no other glycosidase activity and is judged homogeneous. The enzyme has a molecular weight of 130 000 ± 5000 and an isoelectric point of 4.7. The amino acid composition of the enzyme is characterized by high proportion of acidic amino acids and no cysteine residues and a single chain structure of the enzyme is suggested. The enzyme shows maximum activity on p-nitrophenyl-β-d-mannopyranoside at pH 3.5 and 55°C. The presence of 80% of β-sheet structure in the protein and 20.8% of monosaccharides (Gal : 1.3; Man : 7; GlcNAc : 1) could explain this relative high heat stability (up to 2 h at 55°C). Enzyme activity is inhibited by mannose (Ki = 7.85 mM) and the specificity is examined. © 1978.