Biotin-hydrazide groups

Biotin-hydrazide also may be used to couple with carboxylate-containing molecules. Hydrazidcs can be coupled with carboxylic acid groups by using the carbodiimide reaction (Chapter 3, Section 1.1). The carbodiimide activates a carboxylate to an o-acylisourea intermediate. Biotin-hydrazide can react with this intermediate via nucleophilic addition to form a stable covalent bond. 

Biotin-hydrazide has been used to biotinylate antibodies at their oxidized carbohydrate residues (O Shanessy et al., 1984, 1987 O Shanessy and Quarles, 1985 Hoffman and O Shannessy, 1988), to modify the low-density lipoprotein (LDL) receptor (Wade et al., 1985), to biotinylate nerve growth factor (NGF) (Rosenberg et al., 1986), and to modify cytosine groups in oligonucleotides to produce probes suitable for hybridization assays (Reisfeld et al., 1987) (Chapter 27, Section 2.3). 

The following protocol describes the use of biotin-hydrazide to label glycosylated proteins at their carbohydrate residues. Control of the periodate oxidation level can result in specific labeling of sialic acid groups or general sugar residues (Chapter 1, Section 4.4). 

Figure 20.9 Polysaccharide groups on antibody molecules may be oxidized with periodate to create aldehydes. Modification with biotin-hydrazide results in hydrazone linkages. The sites of modification using this technique often are away from the antibody-antigen binding regions, thus preserving antibody activity.

Biotin-Hydrazide Modification of Bisulfite-Activated Cytosine Groups... 

If a free amino group forms a portion of the protein that is essential for activity (e.g., the antigen-combining site for antibody), biotinylation with the succinimide ester will lower or destroy the activity of the protein, and other methods of labeling should be tried. Biotin hydrazide has been used to modify the carbohydrate moieties of antibodies (10,11). Other alternatives are the thiol-reactive biotin maleimide (12) or biotin iodoacetamide (13). 

An analog of this biotinylation reagent with a longer spacer arm also exists. Biotin-LC-hydrazide contains a 6-aminocaproic acid extension off its valeric acid group (Pierce). The increased length of this spacer (24.7 A) provides more efficient interaction potential with avidin or streptavidin probes, possibly increasing the sensitivity of assay systems. The reactions of biotin-LC-hydrazide are identical to those of biotin-hydrazide. 

Dissolve a hydrazide-containing enzyme or other protein at a concentration of 10 mg/ml in 0.1 M sodium phosphate, 0.15 M NaCl, pH 7.2. For the preparation of a hydrazide-activated enzyme see Chapter 16, Section 2.4. For modification with a hydrazide-containing probe, such as biotin-hydrazide, use a concentration of 5 mM in the phosphate buffer. For conjugation through the amine groups of a secondary molecule, dissolve the amine-containing protein at 10 mg/ml in 0.2 M sodium carbonate, pH 9.6. 

Streptavidin Biotin (LSAB) procedure for example. Conjugation with biotin also involves two steps, as biotin must first be derivatized to the biotinyl N hydroxysuccinimide ester or to biotin hydrazide before it can be reacted with the epsilonamino groups of the enzyme. 

Another y-hydrazide derivative of MTX was prepared by Rosowsky and Forsch [333] from a-t-butyl MTX by a mixed anhydride activation of the y-carboxyl group (/-BuOCOCl-Et3N) followed by addition of biotin hydrazide and treatment with trifluoroacetic acid (room temperature, 10 min) to obtain the biotinyl derivative (VIII.228). The overall yield for the coupling and deprotection steps was approximately 30%. 

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