Abstract
Endo-β-N-acetylglucosaminidase H from Streptomyces griseus completely hydrolyzed thyroglobulin Unit A (mannose-N-acetylglucosamine unit) glycopeptides, but did not act on “side-chain*-free” thyroglobulin Unit B (complex heteropolysaccharide unit) glycopeptides. Endo-β-N-acetylglucosaminidase H also did not act on intact or “side-chain-free ” IgG glycopeptides. α-L-Fucosidase [EC 3. 2. 1. 51] treatment did not make the above glycopeptides susceptible to endo-β-N-acetylglucosaminidase H.
[14C]-Acetyl-AsnGlcNAc2Man1 prepared from [14C]-acetyl-AsnGlcNAc2Man5 by α-mannosidase [EC 3. 2. 1. 24] digestion was resistant not only to endo-β-N-acetyl-glucosaminidase H, but also to endo-β-N-acetylglucosaminidase D from Diplococcus pneumoniae.
A disaccharide isolated from a “side-chain-free” bovine IgG glycopeptide by treatment with endo-β-N-acetylglucosaminidase D, followed by α-mannosidase digestion had a probable structure of Manβ1→4GlcNAc, suggesting that a common sequence of the mannose-N-acetylglucosamine unit (Manβ1→4GlcNAcβ1→4GlcNAc→Asn) is present in glycopeptides of complex heteropolysaccharide unit.
We propose that endo-β-N-acetylglucosaminidase H and endo-β-N-acetylglucosaminidase D have opposite specificities; i.e., the former generally hydrolyzes glycopeptides of the mannose-N-acetylglucosamine unit, and the latter generally hydrolyzes “side-chain-free” glycopeptides of the complex heteropolysaccharide unit, and that the two enzymes recognize the structural differences of α-mannosyl residues in the oligomannosyl cores of the two units.
