2006 Volume 18 Issue 99 Pages 73-84
The enzyme which catalyzed deglycosylation of human salivary α-amylase family A(HSA-A) to form salivary α-amylase family B(HSA-B) in saliva was revealed to be an endo-β-N-acetylglucosaminidase. It was named endo-β-N-acetylglucosaminidase HS(Endo HS). Endo HS is specific for complex type asparagine-linked oligosaccharides and can release bi, tri and tetrantennary complex type oligosaccharides from native glycoproteins, glycopeptides and asparaginyl oligosaccharides regardless of the existence of fucosyl residue attached to the proximal GlcNAc residue of oligosaccharides. Endo HS can also transfer these oligosaccharides to various monosaccharides. Furthermore, HSA having oligosaccharides at the two potential glycosylation sites was also found, purified, and named human salivary α-amylase family C(HSA-C). It showed the similar antigenicity for HAS-A and HAS-B. HSA-C has two biantennary complex type oligosaccharides. HSA-C was converted to HSA-B via HSA-A by the action of Endo HS. The multiple form pattern of HSA-C was also converted to the same pattern as that of HSA-B. The existence of HSA-C and Endo HS, and the conversion of HSA-C to HSA-B via HSA-A by the action of Endo HS in human saliva suggest that HSA is glycosylated at the two potential glycosylation sites, secreted into saliva, as HSA-C and then deglycosylated by Endo HS to be the oligosaccharide-deficient glycoisoforms such as HAS-A and HAS-B present in human saliva.
