Effect of nucleotides on thermal stability of ferricytochrome C.

The effect of nucleotides on the structure and thermal stability of ferricytochrome c was studied by differential scanning calorimetry. The association of cytochrome c with ATP and ADP resulted in a decrease in the denaturation temperature of cytochrome c by 7 degrees C and 4 degrees C, respectively, at pH 7.0. AMP did not change the denaturation temperature of cytochrome c at pH 7.0. The ratio between van't Hoff and calorimetric enthalpy of denaturation accounts for the fact that cooperative denaturation of 3-4 molecules of cytochrome c occurred in the presence of ATP at the pH range from 5 to 9. ADP gave rise to the interaction of 2-3 molecules of ferricytochrome c at pH 6-7.5, and AMP did not affect the interaction of protein molecules. Cytochrome c alone also associated at pH 7.5-10. At physiological ionic strength, pH 7.0, only ATP induced an association of ferricytochrome c molecules. No intermolecular interaction of ferricytochrome c molecules was observed at concentrations of NaCl higher than 0.2 mol/l not even in the presence of ATP.