Calorimetric investigation of ribonuclease thermal denaturation.

Abstract

Thermal denaturation of ribonuclease has been investigated by scanning microcalorimetric, spectrophotometric and polarimetric techniques. It is shown that the temperature changes of ribonuclease are of a complicated character and may be subdivided by the temperature region into two qualitatively different stages: (a) the predenaturational stage, at which neither abrupt changes in physico‐chemical properties nor heat absorption occur, but where the protein partial heat capacity considerably grows; (b) the denaturational stage which is accompanied by intensive heat absorption with the abrupt change in all physico‐chemical properties. Judging by the coincidence of the calorimetric and effective enthalpies, there is a transition at this stage between the two states without intermediate thermodynamically stable forms. Enthalpy values of denaturation, temperature of denaturation and denaturational changes of the heat capacity at various pH values are given.