Thermodynamic analysis of thermal transitions in globular proteins. I. Calorimetric study of ribotrypsinogen, ribonuclease and myoglobin

Thermal confonnalional transformations of globular proteins, chymotrypsinogen, ribo‐nudcase and myoglobin in solutions at different pH values were studied microcalorimetrically. It was shown that the heat effects observed in the process of heating have a complicated form and their explanation necessitates an assumption on the existence of two stages of the process separated by temperature: (I) a pre‐denaturational stage where the protein partial heat capacity changes are probably connected with a labilization of the globule structure and (II) a denaturational stage representing a single‐step transition of the protein into a state with a higher enthalpy. Transitions without enthalpy change, the existence of which is shown for the first time in globular proteins, necessitates a more cautions approach to the thennudynamical analysis of different physical parameters on the basis of the van't Hoff equation.