Substrate specificity of mammalian endo-beta-N-acetylglucosaminidase: study with the enzyme of rat liver

The substrate specificity of mammalian endo-β-N-acetylglucosaminidase was studied in detail by using rat liver enzyme. The enzyme hydrolytically cleaves the N,N′-diacetylchitobiose moiety of Manα1 → 6 (Manα1 → 3)Manβ1 → 4GlcNacβ1 → 4R in which R represents either GlcNac → Asn or N-acetylglucosamine. The enzyme can hardly act on the sugar chains with Fucα1 → 3 or 6GlcNac → Asn or N-acetylglucosaminitol as their R residues. The sugar chains substituted at C-3 and C-6 positions of the Manα1 → 6 residue and at C-2 position of the Manα1 → 3 residue by other sugars are also cleaved by the enzyme. The sugar chains substituted at C-4 position of the β-mannosyl residue and at C-2 position of the Manα1 → 6 residue by other sugars are hydrolyzed at one place lower rate. The specificity of the mammalian endo-β-N-acetylglucosaminidase indicates that the enzyme is responsible for the formation of most of the oligosaccharides excreted in the urine of patients with congenital exoglycosidase deficiencies and also explains why large amount of glycopeptides are excreted in the urine of fucosidosis patients.