Abstract
The effect of iodination on anti- p-azophenyltrimethylammonium antibody was determined from a correlation of iodine uptake with the loss in immunological activity and the modification of amino acid residues. Compared to anti- p-azophenylarsonate antibody, whose active site is known to contain tyrosine, both the binding sites and the binding affinity of anti- p-azophenyltrimethylammonium antibody were found to be very resistant to destruction by iodination. Even after the modification of essentially all the iodine-reactive residues, fifty-eight tyrosines, fourteen methionines, sixteen histidines and twenty tryptophans, the antibody retained 14·6 per cent of the binding capacity of the original preparation. Furthermore, the presence of the homologous hapten, p-nitrophenyltrimethylammonium ion, did not protect against the effects of iodination and no preferential uptake of iodine by the active sites was observed upon reiodination after removal of the hapten. These data establish that neither tyrosine nor any other iodine-reactive residue is present at the active center of anti- p-azophenyltrimethylammonium antibody and the gradual losses in immunological activity during extensive iodination are the result of nonspecific changes in the tertiary structure.
Published Version
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