[Calorimetric study of heat denaturation of toxins]

A calorimetric study of reversible heat denaturation of cytotoxin I, neurotoxins I and II in aqueous solution has been carried out. All of them are low molecular proteins from snake venom. Thermodynamic parameters of the transition of the toxins from native to denatured state were determined. Temperature dependences of a specific enthalpy delta dH of the transition were found. It was shown, that upon denaturation the changes in the value of partial heat capacity delta dCp for each of the toxins were constant and did not depend on medium conditions, i.e. composition of a solvent, pH and temperature of the transition. The results of the calorimetric study of the toxins are discussed along with structural peculiarities of low molecular weight proteins (less than 10 000 D) characterized by the amount of van der Waals' interactions between non-polar groups and intramolecular hydrogen bonds.