Carbohydrate-amino acid linkages

Another Fischer achievement was the synthesis of small peptides via the condensation of amino acids. Fischer suggested that there was a common linkage that held pairs of amino acids together in all proteins—the peptide bond. He understood that proteins were tremendously complex, owing to the large number of constituents and the fact of stereoisomerism. By 1916 Fischer had synthesized and characterized 100 peptides, but knew they represented a tiny fraction of what was possible, see also Amino Acid Carbohydrates Isomerism van t Hoff, Jacobus. 

Properties and Structure. a -Acid glycoprotein (a -AGP) has a molecular mass of about 41,000 and consists of a peptide chain having 181 amino acid residues and five carbohydrate units (14,15). Two cystine disulfide cross-linkages connect residues 5 and 147 and residues 72 and 164. The carbohydrate units comprise 45% of the molecule and contain siaUc acid, hexosamine, and neutral hexoses. In phosphate buffer the isoelectric point of the... 

Structures and Types of Carbohydrate-Amino Acid Linkages. 4... 

As mentioned in the Introduction, a variety of unusual carbohydrate -protein linkages is found in Nature. These may be placed in several categories (i) carbohydrates O-glycosylated to jff-hydroxy amino acids (ii) carbohydrates S-glycosylated to cysteine (Hi) carbohydrates N-gly-cosylated to the N-terminal amino group of the protein or (iv) in some... 

One of the most unusual carbohydrate - amino acid linkages so far found in Nature is the thio linkage between glucose or galactose and cysteine.35,40 41 This glycopeptide has not yet been isolated or synthesized. Therefore, in order to obtain 13C-n.m.r. chemical-shift data for... 

The Amino Acid and Carbohydrate Residues in Carbohydrate-Protein Linkages of Mammalian Origin ... 

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. 

The biological activities of several other interleukins also render them likely candidates for therapeutic application. IL-5 represents one such candidate. IL-5 is a 115 amino acid glycoprotein produced mainly by activated T lymphocytes and also by mast cells. It functions as a homodimer, exhibiting a molecular mass of 45 kDa. The individual polypeptide chains interact non-covalently and the overall dimeric structure is stabilized by two interchain disulphide linkages between cysteines 42 and 84 of each chain. Removal or alterations of the cytokine s carbohydrate side-chain does not appear to affect its biological activity. 

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