Mannosyl-oligosaccharide 1,2-α-mannosidase (EC 3.2.1.113, mannosidase 1A, mannosidase 1B, 1,2-α-mannosidase, exo-α-1,2-mannanase, mannose-9 processing α-mannosidase, glycoprotein processing mannosidase I, mannosidase I, Man9-mannosidase, ManI, 1,2-α-mannosyl-oligosaccharide α-D-mannohydrolase) is an enzyme with systematic name 2-α-mannosyl-oligosaccharide α-D-mannohydrolase.
[1][2] It catalyses the hydrolysis of the terminal (1→2)-linked α-D-mannose residues in the oligo-mannose oligosaccharide Man9(GlcNAc)2.
This enzyme is involved in the synthesis of glycoproteins.
Kifunensine is a potent inhibitor of mannosidase I.