Importance of a Good Fit

The ability of enzymes to preorganize reactants for reaction contributes significantly to their efficacy [21]. The excellent shape complementarity observed in antibody-antigen complexes suggests that antibody binding energy could be exploited for this purpose. Antibody catalysts have been developed for bimolecular Diels-Alder reactions to test this supposition. 

The immunological origins of 1E9 have been traced to a family of highly restricted germline antibodies that bind diverse hydrophobic ligands [30]. A precise fit to the 

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In the second step the bas is recognized by the receptor site and the bas-rep complex forms. As was noted above, the complex is generally bonded by inter-molecular forces. The bas is transferred from an aqueous phase to the receptor site. The receptor site is very much more hydrophobic than is the aqueous phase. It follows, then, that complex formation depends on the difference in intermolecular forces between the bas-aqueous phase and the bas-receptor site. The importance of a good fit between bas and receptor site has been known for many years. The configuration and conformation of the bas can be of enormous importance. Also important is the nature of the receptor. If the receptor is. a cleft, as is the case in some enzymes, steric effects may be maximal as it may not be possible for a substituent to relieve steric strain by rotating into a more favorable conformation. In such a system, more than one steric parameter will very likely be required in order to account for steric effects in different directions. Alternatively, the receptor may resemble a bowl, or a shallow, fairly flat-bottomed dish. Conceivably it may also be a mound. In a bowl or dish, steric effects are likely to be very different from those in a cleft. Possible examples are shown in Fig. 1, 2, and 3. 

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