Mannosyl-oligosaccharide 1,2-ñ-mannosidase (, mannosidase 1A, mannosidase 1B, 1,2-ñ-mannosidase, exo-ñ-1,2-mannanase, mannose-9 processing ñ-mannosidase, glycoprotein processing mannosidase I, mannosidase I, Man<sub>9</sub>-mannosidase, ManI, 1,2-ñ-mannosyl-oligosaccharide ñ-<small>D</small>-mannohydrolase) is an enzyme with systematic name 2-ñ-mannosyl-oligosaccharide ñ-<small>D</small>-mannohydrolase. It catalyses the hydrolysis of the terminal (1âÂÂ2)-linked ñ-<small>D</small>-mannose residues in the oligo-mannose oligosaccharide Man<sub>9</sub>(GlcNAc)<sub>2</sub>.
This enzyme is involved in the synthesis of glycoproteins.
Kifunensine is a potent inhibitor of mannosidase I.