Catalysis of the hydrolysis of the alpha-D-mannosyl-(1->6)-beta-D-mannosyl-(1->4)-beta-D-N-acetylglucosaminyl-(1->4)-beta-D-N-acetylglucosaminyl sequence of glycoprotein to alpha-D-mannosyl-(1->6)-D-mannose and beta-D-N-acetylglucosaminyl-(1->4)-beta-D-N-acetylglucosaminyl sequences.
endo-beta-mannosidase activity