CMP-glycoside

Figure 3. Two models for the O-acetylation of Sia in Golgi-membranes of bovine submandibular glands. A, as CMP-glycoside, before the transfer onto nascent glycoconjugates (mucin) and B, after this transfer. OAT, sialate-7(9)-0-acetyltransferase ST, sialyltransferase M, O-acetylisomerase. For further details see the text.

Shaw, L., and Schauer, R., 1988, The biosynthesis of N-glycoloylneuraminic acid occurs by the hydroxylation of the CMP-glycoside of N-acetylneuraminic acid, Biol. Chem. Hoppe-Seyler 369 477-486. 

Schauer, R., Wember, M., and do Amaral, C. F., 1972, Synthesis of CMP-glycosides of radioactive N-acetyl-, N-glycolyl-, A -acetyl-7-O-acetyl- and N-acetyl-8-O-acetylneu-raminic acids by CMP-sialate synthetase from bovine submaxillary glands, Z. Physiol. Chem. 353 883. 

Nucleotides are the phosphoric acid ester of nucleoside, while nucleosides are compounds in which nitrogenous bases (purines and pyrimidines) are conjugated to the pentose sugar (ribose or deoxyribose) by a b-glycosidic linkage. AMP, ATP, ADP, GMP, CMP, UMP are the examples of mononucleotides. 

Thiem and Treder [278] have used immobilised enzymes [216] for the separate syntheses of Af-acetyllactosamine and CMP-iV-acetylneuraminic acid. These were allowed to react in solution in the presence of the sialyltransferase to give the 6 -N-acetylneuraminyl glycoside on the 50 pmol scale. 

Following the enzymatic synthesis of CMP-Neu5Ac, isolated a2-6-sialyl-transferases could be used to introduce sialic acid to the N-acetyl lactosamine derivates a-f in position 6. This afforded a series of trisaccharide derivates Neu5Aca2-6 Gal l-4GlcNAc l-R. The unblocked trisaccharide a [55], the methyl glycoside b [56], the -Asn derivative c [57], the pentapeptide derivative d [58], the allyl e [59], and the pent-4-enyl glycoside f [48] can be prepared in convincing yields (Fig. 6). 

Free sialic acids are used by the enzymes of sialic acid metabolism, CMP-sialate synthase and Neu5Ac aldolase. However the majority of sialic acid-metabolising and -recognising proteins interact with glycosidically bound sialic acid. There-... 

In brief, glycosidation systems similar to that depicted in Fig. 10.3, with regeneration of sugar nucleotides, have been developed with UDP GIcNAc, GDP Man, GDP Fuc, UDP GlcUA, and CMP NeuSAc. Enzymic sialylation will be described in detail in Section 12.4. 

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