Distances of tyrosine residues from a spin-label hapten in the combining site of a specific monoclonal antibody.

The nuclear magnetic resonance spectra of an Fab fragment of a monoclonal antibody specifically directed against a nitroxide spin-label hapten have been recorded at different concentrations of the hapten. The hybridoma producing this antibody was grown on deuterated phenylalanine, tryptophan, and 3,5-dideuteriotyrosine or 2,6-dideuteriotyrosine. Difference spectra--without hapten minus with hapten--were calculated for each concentration of hapten. The difference spectra reveal five well-resolved singlet proton resonance signals from tyrosine deuterated in the 3,5-positions (H 2,6 Tyr) and nine from tyrosine deuterated in the 2,6-positions (H 3,5 Tyr). The measured intensities of these signals as a function of combining site occupation have been interpreted in terms of a theory involving intrinsic line widths (T2), the hapten off-rate (k), and distances to the paramagnetic center. Good agreement with theory is found for all of the isolated proton signals. The best estimate of k is 350 s-1; distances in the range 13 to less than 9 A are calculated. Extension of this analysis to other amino acids is discussed.