Free energy changes in alpha-lactalbumin denaturation.

Previous work has shown that native alpha-lactalbumin (N) is completely denatured by the addition of guanidine hydrochloride (conformation D) but that partially denatured conformations appear in other denaturants. In particular, conformation I appears when the pH is lowered from 5.5 to 2.2 (I2.2) or when LiClO4 is added at pH 5.5 (I5.5). We have now determined the free energy changes for the processes N leads to I5.5, N leads to D5.5, and I2.2 leads to D2.2. We have also estimated the maximum value of the free energy change for the process N leads to I.22, and this allows us to estimate the changes for all conformational changes between any two of these five conformations.