pH on-off switching of antibody-hapten binding by site-specific chemical modification of tyrosine.

Tetranitromethane (TNM) chemically mutates the binding sites of antibodies so that the nitrated antibodies exhibit pH-dependent binding near physiological pH. Three monoclonal antibodies were selectively modified, each under different conditions, with the resultant loss of binding activity at pH > 8 which is recovered at pH < 6. Recovery and loss of binding are ascribed to the protonation and deprotonation, respectively, of the hydroxyl group of the resulting 3-nitrotyrosine side chain (pKa approximately 7) at the binding site of these antibodies. pH on-off dependency of binding activity, common to all TNM-modified antibodies studied by us so far, may find use in a variety of applications in which controlled modulation under mild conditions is required.