Necessary for the catabolism of N-linked carbohydrates released during glycoprotein turnover. Hydrolysis of terminal, non-reducing alpha-D-mannose residues in alpha-D-mannosides. Binds 1 zinc ion per subunit. Homodimer. Processed into 5 peptides of 35/38 kDa (A), 11/13 kDa (B) and 22 kDa (C), 38 kDa (D) and 13/15 kDa (E). The A, B and C peptides are disulfide-linked into a 67 kDa complex. Heavily glycosylated. Some sugar chains are of the high-mannose type. Defects in MAN2B1 are the cause of lysosomal alpha-mannosidosis (AM). AM is a lysosomal storage disease characterized by accumulation of unbranched oligosaccharide chains. The disease manifests itself by head tremor, aggressive tendency, ataxia, failure to thrive, and early death. Belongs to the glycosyl hydrolase 38 family.