Effect of Solution pH and Composition on Horse Liver Alcohol Dehydrogenase Thermostability

The influence of solution composition (pH, salts, and chelant) on the thermostability of horse liver alcohol dehydrogenase was studied by differential scanning calorimetry (DSC) in the pH range from7.51 to 9.50 and showing the enzyme catalytic activity. The experiments demonstrated that the effect of increasing pH on the heat denaturation temperature of the enzyme was slight, but the denaturation enthalpy was considerably increased, indicating the enzyme conformation alteration by changing pH and the presence of enthalpy-entropy compensation. The effect of ionic strength on thermostability was not noticeable, i.e., the electrostatic interactions were not a dominant factor for the thermostability. The anions Cl⁻ and SCN⁻ imposed diverse influence upon the enzyme thermostability, and SCN⁻can reduce the thermostability considerably. The chelant 1,10-phenanthroline, which can reversibly bind together with the zinc ions functioning the catalytic action in the enzyme molecules, increases the thermostability considerably. The hydration of the enzyme plays an important role to the thermostability. This revised version was published online in July 2006 with corrections to the Cover Date.