DSC measurements have been accomplished in aqueous solutions of bovine pancreatic ribonuclease A (RNAase A) in the presence
of subsaturating amounts of 3′ cytidine monophosphate (3′ CMP) and 2′ cytidine monophosphate (2′ CMP) atpH 5.0 and 5.5. In these conditions the experimental profiles do not conform to a one-step unfolding process. It can be emphasized,
as a general phenomenon, that a strong linkage between the temperature-induced protein unfolding and the ligand binding, when
the ligand is less than the saturation level, causes marked distortions from a two-state transition. A purely equilibrium
thermodynamic analysis gives a correct account of this behaviour and allows to simulate calorimetric curves. It is thus possible
to obtain, in an indirect manner, information about the thermodynamic parameters concerning the binding process, namely the
association constant and the binding enthalpy. The values ofKb and ΔbH for 3′CMP and 2′CMP, so determined, are consistent with the literature data.