THERMODYNAMIC CONSEQUENCES OF THE REMOVAL OF A DISULFIDE BRIDGE FROM HEN LYSOZYME

Differential scanning calorimetry experiments as a function of pH have been carried out for native hen egg white lysozyme and a three-disulphide derivative (CM6,127-lysozyme). The results indicate that the enthalpy (ΔH298) and heat capacity changes (ΔCp) for unfolding are closely similar for the two proteins. This shows that the substantial reduction (25 °C at pH 3.8) in Tm resulting from removal of the 6-127 disulphide bond can, to a good approximation, be attributed totally to an increase in the entropy difference between the native and denatured states. The significance of this result for understanding the factors influencing the stability of folded proteins is discussed. © 1992.