Studies on the Biosynthetic Mechanism of Bioactive Sulfated Glycosaminoglycans

(1)以小鼠乳腺细胞瘤微粒体片段为酶源，以UDP-GalNAc为糖供体，以合成糖丝氨酸GlcAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-O-Ser为糖受体，观察到GalNAc的转移。然而，这种联系被发现是α -而不是β -连接的。这与我们先前使用从胎牛血清中纯化的酶制剂获得的观察结果一致。(2)以GlcAbeta1-3Gal(4-O-sulfate) β - 1- 3galbeta1 -4 - ylβ - o - ser为糖受体时，没有观察到上述活性，说明硫酸盐基团抑制了α - galnac转移酶反应。(3)另一方面，在类似的培养条件下，除了UDP-GlcNAc作为糖供体外，没有观察到预期用于肝素生物合成的α - glcnac转移酶活性。然而，以六糖[GlcAbeta1-4GlcNAcalpha1-4]_2-GlcAbeta1-4aMan （aMan，无水甘露糖）为受体，观察到良好的GlcNAc转移酶活性，证实了肝素链聚合活性。(4)以上观察结果似乎表明，硫酸软骨素和硫酸肝素/硫酸肝素的生物合成分选机制存在结构要求或未报道的中间体。

(1)Using mouse mastcytoma microsomal fraction as an enzyme source, UDP-GalNAc as a sugar donor and a synthetic glycoserine GlcAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-O-Ser as an sugar acceptor, a GalNAc transfer was observed. However, the linkage was found to be alpha-but not beta-linked. This was in accordance with our previous observation obtained using the enzyme preparation purified from fetal bovine serum.(2)The above activity was not observed with GlcAbeta1-3Gal(4-O-sulfate)beta1-3Galbeta1-4Xylbeta1-O-Ser as an sugar acceptor, indicating that the sulfate group inhibited the alpha-GalNAc transferase reaction.(3)On the other hand, no alpha-GlcNAc transferase activity expected for heparin biosynthesis was observed when assayd under similar incubation conditions except that UDP-GlcNAc was used as a sugar donor. However, a good GlcNAc transferase activity was observed with a hexasaccharide [GlcAbeta1-4GlcNAcalpha1-4]_2-GlcAbeta1-4aMan (aMan, anhydromannose) as an acceptor, confirming the heparin chain polymerization activity.(4)The above observations seem to indicate that there are structural requirements or unreported intermediates necessary for the biosynthetic sorting mechanisms of chondroitin sulfate and heparin / heparan sulfate.