Hapten conjugating amine-containing

The above methods were utilized to conjugate a carboxyl group on a hapten to an amino residue on a protein. Obviously, the above reactions could be, and have been, utilized to conjugate an amino residue on a hapten to the carboxyl residues on proteins. However, there are additional methods which have proven useful for conjugating amine containing haptens to proteins. ... 

The Mannich reaction can be used for the immobilization of certain drugs, steroidal compounds, dyes, or other organic molecules that do not possess the typical nucleophilic groups able to participate in traditional coupling reactions (Hermanson et al., 1992). It also can be used to conjugate hapten molecules to carrier proteins when the hapten contains no convenient nucleophile for conjugation (Chapter 19, Section 6.2). In this case, the carrier protein contains the primary amines and the hapten contains at least one sufficiently active hydrogen to participate in the condensation reaction. 

The crosslinking scheme using this method can make use of the native e- and N-terminal amines on carrier proteins as the source of primary amine for the condensation reaction. Added to the conjugation reaction then is formaldehyde and the desired hapten to be coupled containing an appropriately active hydrogen. 

To increase the yield of conjugated hapten using this procedure, cBSA is used as the carrier protein in the method described below (see Section 2.1, this chapter for additional information on this carrier). The greater density of amine groups on cBSA available for participation in the Mannich reaction over that available on native proteins provides better results in coupling active-hydrogen-containing haptens. 

Hapten molecules containing aldehyde residues may be crosslinked to carrier molecules by use of reductive animation (Chapter 3, Section 4). At alkaline pH values, the aldehyde groups form intermediate Schiff bases with available amine groups on the carrier. Reduction of the resultant Schiff bases with sodium cyanoborohydride or sodium borohydride creates a stable conjugate held together by secondary amine bonds. 

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