| Summary: | <p>Data from ¹H nuclear magnetic resonance studies on the Fv fragment of protein 315, a Dnp-binding BALB/c mouse lgA(λ<sub>2</sub>) myeloma protein, have been used to refine a predicted structure of the combining site of the protein. The Dnp-binding subsite in the modified structure is composed of the side chains of three aromatic amino acids Trp 93<sub>L</sub>, Tyr 3<sup>4</sup><sub>L</sub> and 3<sup>4</sup><sub>H</sub>. A fourth aromatic amino acid residue is close to the side chain-NH-CH 2 -group, this is Tyr 33 H - The antibody-hapten binding is a simple encounter process, which causes no extensive conformation change in the Fv fragment.</p> <p>A method for paramagnetic structural studies has been devised using Dnp derivatives with cllgophosphate side chains, which create a specific manganese binding site on the Fv fragment-hapten complex. The distances from the bound metal ion to the imidazole side chains of two of the three hlstldine residues of protein 315 have been determined.</p> <p>¹H nuclear magnetic resonance has been used to study the histidine residues of the Fv fragment of protein 315. It has been shown that one of the three histidine residues (102<sub>H</sub>) is close to the combining site, but that this residue does not participate directly in binding haptens. <sup>31</sup> P nuclear magnetic resonance studies have shown the presence of a positively charged amino acid side chain near the entrance of the combining site of the Fv fragment. This residue has been identified as Arg 95<sub>L</sub>.</p> <p>The mode of binding of trini trophenyl derivatives to the Fv fragment has been studied by <sup>1</sup>H nuclear magnetic resonance. It is concluded that these haptens, when bound to the Kv fragment, make contacts with the same amino acid side chains as Dnp derivatives.</p>
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