[Cold denaturation of staphylococcal nuclease]

It has been shown that the structure of staphylococcal nuclease breaks down reversibly both at a temperature increase above 20 degrees C and at its decrease. Both the heat and cold denaturations of protein are well approximated by a transition between two states differing in heat capacity, which means that the whole protein molecule represents a unique cooperative system with a well developed hydrophobic core. The transfer to a denatured state at a temperature decrease is accompanied by heat release and leads to a complete loss of the unique tertiary structure, decrease of the helicity and increase of the hydrodynamic volume of the molecule.