Haptenic group

The concept of catalytic antibodies was suggested succinctly by Jencks. If complementarity between the active site and the transition state contributes significantly to enzymatic catalysis, it should be possible to synthesize an enzyme by constructing such an active site. One way to do this is to prepare an antibody to a haptenic group which resembles the transition state of a given reaction. The combining sites of such antibodies should be complementary to the transition state and should cause an acceleration by forcing bound substrates to resemble the transition state. ... 

Since the components of each set were eluted by the same hapten group, galactose or lactose, and each protein combines with the same structural unit of the antigen, the individual proteins of each set have been designated as isoantibodies. This definition is a more restrictive definition of an isoantibody than is employed by immunologists (32) but is in line with the terminology employed by enzymologists for multi-molecular forms of enzymes (33). 

An enzyme immunoassay using adenosine deaminase as the enzyme label has been described (318). Potentiometric rate measurements were made with an ammonia gas-sensing electrode. The immunoassay system employed is based on competition between a model haptenic group, dinitrophenyl (DNP) covalently coupled to adenosine deaminase, and free DNP hapten for the available binding sites on the anti-DNP antibody molecules. The detection limit is 50 ng antibody. 

Figure 8-6. A haptenic group, DNP covalently bound to the e-amino group of a lysine residue. The solid line encloses the hapten and the broken line encloses what might represent a determinant. Note that residues R, and are found in very different areas of the polypeptide chain even though both residues are part of the antigenic determinant.

This is a simple, direct procedure - that does not require the preparation and isolation of an active derivative. The coupling procedure is carried out directly with the hapten, and the product usually contains 1 -25 hapten groups per molecule of albumin. As an example of this method, the coupling of cortisone-21-hemisuccinate to protein is illustrated (Fig. 2). The haptenic group was converted in situ to an acid anhydride, which could then react in an aqueous-acetone solution with the amino groups of serum albumin. 

Generally, the haptenic group has an absorbance spectrum that can allow one to differentiate it from the protein carrier. This is particularly true for azo derivatives, which absorb in the visible range. However, even if there is overlap in the two spectra, reasonably accurate determinations of the number of haptenic molecules per carrier protein can be determined from difference spectra. 

EW Voss Jr, RW Watt. Steric orientation of hapten groups and the effects. Immunochemistry 14 741, 1977. 

B-cell determinants or haptenic determinants, as they are frequently called, are comparatively well defined with regard to dimensions and specificity relationships. The problem of their size has attracted considerable interest during the last two decades and seems now satisfactorily elucidated. A recent careful review of these aspects has been provided by Goodman (1975). It has been known for some time that haptenic groups such as DNP and BPO do not comprise the entire deter-... 

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