Biochemical studies of mucin cleaving enzyme and gastric mucus glycoprotein

粘液糖蛋白或粘蛋白是保护组织和细胞免受各种侵袭剂攻击的重要成分。粘蛋白中寡糖和0-糖苷键的酶解将大大加快粘液糖蛋白的蛋白质和糖部分的结构研究。粘液糖蛋白的降解酶是从链霉菌的培养基中获得的。OH-11242，其中添加猪胃粘液糖蛋白作为唯一的碳源。从培养基中提取的粗酶制剂除含有外糖苷酶和蛋白酶外，还含有内糖苷酶。建立了吡啶层状低聚糖(PA)的高效液相色谱(HPL C)测定方法。从该培养基制得的低聚糖的大小对应于7-14个葡萄糖低聚物。从PA-寡糖中提取的还原末端糖确定为半乳糖、N-乙酰氨基葡萄糖和N-乙酰氨基葡萄糖。对内切糖苷酶进行了部分纯化，证明存在一种新型的内切糖苷酶，它不仅能释放半乳糖β1-3GalNAc，还能通过水解GaInAe和丝氨酸(Thr)之间的0-糖苷键释放出其他较大的寡糖。大鼠胃内有两种截然不同的粘液糖蛋白亚基，一种为4.4×10~(-5)mW，另一种为6×10~(-6)mW。它们在胃中的位置不同。胃粘液糖蛋白低聚糖的硫酸盐基团在胃体和胃窦中的位置也不同。

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.