Partial purification and characterization of the glucosidases involved in the processing of asparagine-linked oligosaccharides

A glucosidase preparation with activity toward certain glucose-containing oligosaccharides was partially purified from calf liver membranes by Triton X-100 solubilization and DEAE-cellulose and hydroxylapatite chromatography. The enzyme preparation hydrolyzed the glucose residues from (glucose)₁,(mannose)₉(N-acetylglucosamine)₁, and (glucose)₂(mannose) ₉(N-acetylglucosamine)₁ but was totally inactive toward (glucose)₃(mannose)₉(N-acetylglucosamine) ₁. In contrast, crude membrane preparations of the calf liver were active toward all three substrates. The partially purified enzyme had a pH optimum of 6.7 and was very unstable in the absence of added 20% glycerol. The rate of glucose release from the one-and two-glucose-containing oligosaccharides was significantly decreased when four or five of the mannose residues were first removed from the substrate. The release of glucose from (glucose)₁(mannose)₉(N-acetylglucosamine)₁ was inhibited by p-nitrophenyl-α-d-glucoside much more effectively than by p-nitrophenyl-β-d-glucoside, suggesting that this glucose residue may be linked α to the mannose residue. We conclude that during oligosaccharide processing at least two different glucosidases are involved in glucose removal.