Temporal evolution of the sensitivity to tetranitromethane of the active site of anti-Tobacco mosaic virus antibodies.

Rabbit anti-TMV antibody taken 9 days after antigen injection is inactivated by much lower concentrations of tetranitomethane (TNM) than anti-body taken after 30 days. This change in sensitivity to TNM occurs in a very heterogeneous population of molecules, including IgM and IgG classes, but the affinity of the antibody remains unchanged. Thus, the phenomenon is not the result of selection of antibody-producing cells under the influence of antigen. Inactivation of early anti-TMV antibody appears to result from the nitration of one tyrosyl residue per Fab fragment. This tyrosine is probably located in the heavy chain and most probably in the variable portion. The moderate sensitivity of late anti-body to TNM is attributed to the lower reactivity of a tyrosine in the active site, and to the fact that nitration of this tyrosine does not inactivate the binding site. The suggested interpretation is that the majority of molecules of a very heterogeneous anti-TMV antibody pool may have a common structure in their active site during the early stage of the antibody response. This may later be replaced in most molecules by different structures.