Affinity labeling of the heavy and light chains of a myeloma protein with anti-2,4-dinitrophenyl activity

A mouse myeloma protein with high affinity for 2,4-dinitrophenyl (Dnp) ligands was reacted with the bromoacetyl derivatives of N-Dnp-ethylenediamine and (epsilon)-N-Dnp-L-lysine. Up to 1.4 sites per protein molecule were covalently labeled. The labeling reactions were essentially completely blocked by a large excess of Dnp ligands that do not combine covalently (e.g., (epsilon)-Dnp-L-lysine). Analyses of the labeled protein revealed that the bromoacetyl derivative of N-Dnp-ethylenediamine reacted exclusively with tyrosyl in the light chain, while the derivative of (epsilon)-Dnp-L-lysine reacted exclusively with lysyl in the heavy chain. The findings support the conclusion that chains are involved in forming specific combining sites.