Specific Excitation Energy Transfer from Antibodies to Dansyl‐Labeled Antigen

The “loop” peptide region of hen egg‐white lysozyme was labeled with the dansyl group. The binding of the labeled peptide to the anti‐“loop” antibodies led to a specific excitation energy transfer from the antibody to the dansyl group on the hapten. This sensitized fluorescence was used for quantitative evaluation of the binding and homogeneity parameters of the “loop”‐anti‐“loop” interaction. The association constant observed was 3.2 × 106M−1 and the homogeneity index was 0.98 ± 0.05, in excellent agreement with values obtained by equilibrium dialysis.