[Temperature changes in ribonuclease]

Deuteroexchange kinetics of ribonuclease is studied by the change of IR-spectra in the range of 1400--1900 cm-1 at different temperatures in solutions with two pD values, 2.6 and 5.1. It is shown that in the pre-denaturational temperature range the enthalpy of unfolding is 1.5 kcal/mol, i. e. two orders lower than the enthalpy of unfolding in the denaturational temperature range (100--120 kcal/mol). Thus in the pre-denaturational range of temperatures the disclosure of a compact protein structure can proceed at the expense of separate non-cooperative disruptures of bonds. However, the concentration of these disruptures is so low that they cannot give an explanation to the observed pre-denaturational macroscopic changes of protein.