Carbohydrate or glycoproteins

The appropriate protocols for diamine modification of various carbohydrate or glycoprotein derivatives may be found in the indicated sections. 

Figure 14.19 Aldehyde-containing molecules, such as periodate-oxidized carbohydrates or glycoproteins, can be coupled to hydrazide-particles to form a hydrazone bond. This bond can be further stabilized by reduction...

Hydrazide-containing PEG-biotinylation reagents provide reactivity with carbonyl groups (e.g., aldehydes) to label carbohydrates or glycoproteins via hydrazone bond formation (Figures 18.19 and 18.20). The hydrazide group also may be coupled with carboxylate-containing... 

The ethylene diamine-dextran derivative may be used for the coupling of carboxylate-contain-ing molecules by the carbodiimide reaction, for the coupling of amine-reactive probes, or to modify further using heterobifunctional crosslinkers. The hydrazide-dextran derivative may be used to crosslink aldehyde-containing molecules, such as oxidized carbohydrates or glycoproteins. 

There are many glycosylation mutants of cultured mammalian cells and yeast. They have been selected as rare survivors of treatments that kill cells expressing a particular carbohydrate or glycoprotein at the cell surface. For example, plants produce a variety of proteins, called lectins, which bind to cell surface oligosaccharides. Lectins are toxic to mammalian cells. They can be used to select for mutants that no longer bind the lectin because they lack a particular carbohydrate at the cell surface. Such glycosylation mutants have low amounts of glycoproteins that require carbohydrates for stable expression. 

Glycoproteins or mucoproieins. Compounds of proteins with carbohydrates. All glycoproteins contain a hexosamine and usually sulphate, ethanoate and glucuronic acid. The carbohydrate-protein linkages are, in some cases covalent and in others of the salt type. Aqueous solutions of glycoproteins are extremely viscous. 

Antibodies against sugars (carbohydrate residues) can be difficult to obtain and lectins are a solution to these problems. Lectins are naturally occurring plant and animal proteins or glycoproteins that selectively bind noncovalently to carbohydrate residues. Lectins can be labeled directly or secondary antibodies against lectins enables the use of other immuno techniques (30) including electron microscopy (31). 

Glycoproteins are proteins that have been modified by the addition of one or more carbohydrate groups. Glycoproteins include blood group substances, among many others. 

Proteins with molecular weights in the millions are the major constituents of all living cells. Simple proteins are hydrolyzed only to amino acids. Coqjugated proteins are hydrolyzed to amino acids and nonpeptide substances known as prosthetic groups. These prosthetic groups include nucleic acids of nucieoproteins, carbohydrates of glycoproteins, pigments (such as hemin and chiorophyli) of chromoproteins, and fats or lipids of lipoproteins. 

It would seem, then, that the carbohydrate portions of glycolipids or glycoproteins, or both, serve a regulatory role in cell division of tissues capable of rapid proliferation. Fucolipids also seem to be involved in these control processes, although no specific biological effect has been suggested for the fucopyranosyl units within these gl yeans. 

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