CALORIMETRIC INVESTIGATION OF THERMAL-STABILITY AND LIGAND-BINDING CHARACTERISTICS OF DISULFIDE-BOND-CLEAVED RIBONUCLEASE T-1

A combination of differential titration calorimetry and differential s canning calorimetry was used to study the effect of disulfide bond cle avage and reaction with iodoacetamide of ribonuclease T-1 on both the binding of nucleotides and the thermal stability of the free enzyme sp ecies. Although guanosine monophosphates still bind to the active site of the modified protein the transition temperature of unfolding and t he transition enthalpy decrease drastically indicating a relatively lo ose structure. The calorimetric data presented in this study suggest a cooperative linkage between the site of the disulfide bonds, the liga nd-binding site, and the general thermodynamic stability of the enzyme .