A common target for protein modification is the carbohydrate portion of glycoproteins, which can be reacted with hydrazide derivatives of biotin. Oxidative treatment of glycoproteins using 10 mM periodate is used to generate reactive aldehydes from the cis-diols of a variety of carbohydrate moieties.
An aldehyde can be reacted specifically with a hydrazide group at pH 4 to 6, forming a stable hydrazone linkage. Sialic acid residues on glycoproteins can be specifically oxidised with sodium periodate (NaIO₄) under mild conditions. At 1 mM periodate and a temperature of 0 °C, oxidation is restricted primarily to sialic acid residues. Sialic acid residues also can be biotinylated with hydrazide derivatives by pretreatment with neuraminidase to generate galactose groups. The galactose and N-acetylgalactosamine residues on whole cells can be selectively biotinylated with Biotin-Hydrazides by further treatment with galactose oxidase. This enzyme will convert the primary hydroxyl groups on these sugars to their corresponding aldehydes.
Biocytin-Hydrazide: Can be used to label DNA and RNA through cytosine residues. More water soluble than Biotin-LC-Hydrazide.
Biotin-Hydrazide: Carbohydrate reactive. Must be dissolved in DMSO before adding to aqueous buffer.
Biotin-LC-Hydrazide: Use the EDC crosslinker to couple this analogue to carboxyl (–COOH) groups. Water soluble. Longer chain length for reduction of steric hindrance.
Biotin-PEG4-Hydrazide: Water soluble analogue of Biotin-LC-Hydrazide. PEG-based spacer arm increases solubility of labeled molecules.