Sialic acids into glycoproteins

Gross, H. J., Brossmer, R. (1988). Enzymatic introduction of a fluorescent sialic acid into oligosaccharide chains of glycoproteins. Eur. J. Biochem., 177, 583-589. 

Modified with peracetylated iST-azidoacetylmannosamine (Ac ManNAz) was added to CHO cell lines containing the recombinant glycoprotein GlyCAM-Ig, and this resulted in metabolic incorporation of the corresponding N-azidoacetyl sialic acid into its glycans. 

Molnar, J., 1967, Glycoproteins of Ehrlich ascites carcinoma cells. Incorporation of ( C)glucosamine and ( C)sialic acid into membrane proteins. Biochemistry 6 3064-3075. 

The scientific work of Gottschalk falls into three, well-defined periods. His early work was mainly in the general area of the metabolism of carbohydrates and of biologically related compounds. Then, about 1947, he became involved in studies on the interaction between the influenza virion and the surface of the red cell, and this led him to his important work on sialic acid. During the last period, Gottschalk extended his interest to the general chemistry and biochemistry of glycoproteins. 

Enzymic hydrolysis is a useful tool for the identification of carbohydrate linkages, as well as for hydrolysis of the (labile) sialic acids. Neeser developed a method wherein the sialic acids are enzymically hydrolyzed and, simultaneously, enzymically converted into stable 2-amino-2-deoxymannose derivatives. This allows determination of carbohydrate constituents of glycoproteins in a single flask. 

These studies demonstrating a protective effect of sialic acid residues on serum glycoproteins provide an explanation for earlier, conflicting observations about the biological effect of, for example, desialylated erythropoietin, which stimulates erythropoiesis only after direct application to bone-marrow cell-cultures, and not after injection into the blood stream.469 In the latter experiment, only the native, sialylated hormone was active. Rapid clearance and inactivation of follicle-stimulating hormone,470 or interferon,471 after treatment with sialidase may be explained by uptake into liver cells. 

A similar mechanism is apparently responsible for removing old erythrocytes from the mammalian bloodstream. Newly synthesized erythrocytes have several membrane glycoproteins with oligosaccharide chains that end in NeuSAc. When the sialic acid residues are removed by withdrawing a sample of blood, treating it with sialidase in vitro, and reintroducing it into the circulation, the treated erythrocytes disappear from the bloodstream within a few hours those with intact oligosaccharides (erythrocytes withdrawn and reintroduced without sialidase treatment) continue to circulate for days. 

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