Thermodynamics of the interaction of epsilon-dinitrophenyl-L-lysine and the subunits (Fab) of bovine colostral immunoglobulin G1 anti-dinitrophenyl antibody.

Investigation of the binding of epsilon-DNP-1-lysine to the subunits (Fab') of bovine colostral IgG1 anti-DNP over a wide range of temperatures yielded non-linear van't Hoff plots with curvatures which were indicative of large positive heat capacity changes. Thermodynamic functions which were calculated using a non-linear least-squares procedure revealed an enthalpy-entropy compensation mechanism for binding. While the enthalpy factor was the driving force for the hapten-subunit interaction(s) at low temperatures, the entropy factor assumed greater importance with increasing temperatures. In addition, the enthalpy-entropy compensation plot for the interaction of epsilon-DNP-1-lysine with bovine colostral Fab' anti-DNP, intact anti-DNP IgG1 and rabbit IgG anti-DNP revealed a constant compensation temperature (T degrees c) of 27 degrees which might be considered as indicative of a single kind of protein-solvent conformation.