Biochemical studies of mucin cleaving enzyme and gastric mucus glycoprotein

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Mucus glycoproteins, or mucins, are important components which protect tissues and cells from various, attacking agents. Enzymatical cleavage of oligosaccharides and 0-glycosidic linkage in mucin should greatly expedite structural studies on the protein and sugar part of mucus glycoproteins.The degradation enzymes of mucus glycoproteins were obtained from the culture medium of Streptomyces sp. OH-11242 in which porcine gastric mucus glycoproteins were added as the only source of carbon. A crude enzyme preparation from the culture medium contained endo-glycosidases besides exo-glycosidases and proteases. Detection method of the enzyme activity by HPLC analysis of pyridylaminated(PA) oligosaccharide was developed. The size of oligosaccharides prepared from the medium corresponded to 7-14 glucose oligomers. Reducing end sugars as PA-sugars from PA- oligosaccharide was determined to be galactose, N-acetylglucosamine and N-acetylglucosamine. The endo-glycosidase was partially purified and concluded the presence of a new type of endo-glycosidase liberating not only Gal beta 1-3GalNAc but also other larger oligosaccharides by hydrolysis of the 0-glycosidle linkage between GaINAe and Ser(Thr).Further studies of the structure of rat gastric mucus glycoproteins were carried out. There are two distinct types of mucus glycoprotein subunits in rat stomach ; one is 4.4 X10^5 and the other is 6 X10^6 MW. Their location was differed in the stomach. Sulfate group locations on oligosaccharides of gastric mucus glycoprotein were also differed in the corpus and antrum.