Protein quantitation on both branches of the Heidelberger curve by monitoring the kinetic of immunoprecipitation.

For every immunochemical protein quantitation, one must consider the ambiguity of concentration-dependent signals. In immunoprecipitation reactions, where such a phenomenon occurs, the problem has not yet been adequately addressed. Several methods have been cited, which claim to permit an exact concentration determination on the basis of two independent measurements. In the present paper a method is described, in which a concentration determination is unequivocally made through the simultaneous measurement of two (inter-related) reaction parameters. The maximum velocity (Vmax) of the immunoprecipitation and the time (tmax), which was required for the reaction to attain Vmax, are measured simultaneously. Specific test parameters are discussed for the routine protein quantifications. Based on the measurement of 83 samples with pathological immunoglobulins, the findings of this method are compared with those of the classical radial immunodiffusion.