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. Processed into 3 peptides of 72 kDa, 41 kDa and 12 kDa. Defects in MAN2B1 are the cause of lysosomal alpha-mannosidosis (AM). AM is a lysosomal storage disease characterized by accumulation of unbranched oligosaccharide chains. Belongs to the glycosyl hydrolase 38 family.