Glycoproteins hydrazide-protein

Hydrazide groups can react with carbonyl groups to form stable hydrazone linkages. Derivatives of proteins formed from the reaction of their carboxylate side chains with adipic acid dihydrazide (Chapter 4, Section 8.1) and the water-soluble carbodiimide EDC (Chapter 3, Section 1.1) create activated proteins that can covalently bind to formyl residues. Hydrazide-modified enzymes prepared in this manner can bind specifically to aldehyde groups formed by mild periodate oxidation of carbohydrates (Chapter 1, Section 4.4). These reagents can be used in assay systems to detect or measure glycoproteins in cells, tissue sections, or blots (Gershoni et al., 1985). 

Figures Selective protein modification using a keto amino acid, p-acetyl-L-phenylalanine. (a) Labeling of fluorescein hydrazide to the Z domain protein. Only the mutant protein containing p-acetyl-L-phenylalanine was labeled and became fluorescent, (b) A general method for preparing glycoprotein mimetics with defined glycan structure.

In glycoprotein detection systems the carbohydrate portions of proteins are oxidized with sodium metaperiodate to generate aldehydes that can react with hydrazides. A biotin hydrazide is used to attach biotin onto the oxidized carbohydrates and horseradish peroxidase-conjugated streptavidin is used for chemiluminescence-based detection (Glycoprotein Detection Module, Amersham Biosciences, Uppsala, Sweden). 

Higgins et al. synthesized a biotin-functionalized terthiophene 2.210 by reaction of biotin hydrazide and a terthiophene which was functionalized by a succinimidyl active ester (Chart 1.43) [299]. The copolymerization of 2.210 with terthiophene on a Pt electrode formed poly(terthiophene) films containing intact biotin moieties. The binding of 5 x 10 " mol of the glycoprotein avidin to the pendant biotin units of the polymer film resulted in a positive shift of the oxidation potential due to specific inferactions and blocking of the ion transport to and from the polymer by the bound protein. 

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