Calorimetric Investigation of Thermal Stability and Ligand‐binding Characteristics of Disulfide‐bond‐cleaved Ribonuclease T1

A combination of differential titration calorimetry and differential scanning calorimetry was used to study the effect of disulfide bond cleavage and reaction with iodoacetamide of ribonuclease T1 on both the binding of nucleotides and the thermal stability of the free enzyme species. Although guanosine monophosphates still bind to the active site of the modified protein the transition temperature of unfolding and the transition enthalpy decrease drastically indicating a relatively loose structure. The calorimetric data presented in this study suggest a cooperative linkage between the site of the disulfide bonds, the ligand-binding site, and the general thermodynamic stability of the enzyme.