Affinity site labeling of a mouse myeloma protein which binds dinitrophenyl ligands.

A mouse myeloma protein of the immunoglobulin A class, which specifically binds dinitrophenyl ligands, has been successfully affinity labeled (site-directed labeling) with several diazonium reagents, leading to inactivation of the combining sites. The labeling reagents reacted only with tyrosine residues of light chain origin. The 7S subunit of the myeloma protein appears to contain only one reactive site.