Studies on the Biosynthetic Mechanism of Bioactive Sulfated Glycosaminoglycans

(1)以小鼠肥大细胞瘤微粒体组分为酶源，UDP-GalNAc为糖供体，人工合成糖丝氨酸GlcAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-O-Ser为糖受体，观察到GalNAc转移。然而，这种关联被发现是阿尔法关联的，而不是贝塔关联的。这与我们用从胎牛血清中提纯的酶制剂所观察到的结果一致。(2)在GlcAbeta1-3Gal(4-O-sulfate)beta1-3Galbeta1-4Xylbeta1-O-Ser作为糖受体的情况下，没有观察到上述活性，表明硫酸盐基团抑制了α-GalNAc转移酶的反应。然而，以六糖[GlcAbeta1-4GlcNAcalpha1-4]_2-GlcAbeta1-4aMan(Aman，脱水甘露糖)为受体，观察到了良好的GlcNAc转移酶活性，证实了肝素链聚合活性。(4)上述观察似乎表明，硫酸软骨素和肝素/硫酸肝素的生物合成分选机制需要有结构要求或未见报道的中间体。

(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.