New Evidence of the Substrate Specificity of Endo-β-N-Acetylglucosaminidase D1

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Abstract
The susceptibility of a variety of oligosaccharides to endo-β-N-acetylglucosaminidase D was investigated. The oligosaccharides having the structures of Manα1→6 (GlcNAcβ1→4Manα1→3)Manβ1→4GlcNAcβ1→4(±Fucal→6)GlcNAcOT, derived from complex type triantennary sugar chains, released ± Fucal→6GlcNActyr upon incubation with the enzyme at almost the same rate as Manα1→6(Manα1→)Manβ1→4GlcNAcβ1→4GlcNAcOT. When the reaction products were reduced with NaB3H4 and analyzed by Bio-Gel P-4 column chromatography, a new radioactive peak was detected in both cases. This new radioactive oligosaccharide was confirmed to be Manαl→6(GlcNAcβ1→4Manα1→3)Manβ1→4GlcNAcOT in the former case and Manαl→6(Manα1→3)Manβ1→4GlcNAcOT in the latter. These results indicated that endo-β-N-acetylglucosaminidase D does not require the presence of a free hydroxyl group at the C-4 position of the α-mannosyl residue of the trisaccharide glycon: Manα1→3Manβ1→4GlcNAcβ1→.