Thermodynamic characterization of partially denatured states in the denaturation process of bovine alpha-lactalbumin by inorganic denaturants.

In an attempt to understand the specific effect of inorganic protein denaturants, lithium cation and perchlorate anion, upon the molecular conformation of bovine alpha-lactalbumin and to characterize the denatured states of the protein and the denaturation processes, themodynamic studies on the reversible unfolding of the protein in the presence of lithium chloride, lithium perchlorate and sodium perchlorate were made by means of circular dichroism and ultraviolet absorption measurements. The denaturation reaction caused by lithium chloride was found to take place in a three-state type, while that caused by the two perchlorates in a two-state type. The latter produces the same denatured state as the acid does on the protein, the state where the helical structures remain unchanged. The former produces two kinds of the denatured state, one being a less unfolded state than the acid denatured one and the other a fully unfolded state which is identical with the finally denatured state induced by organic denaturants such as guanidinium chloride, guanidinium thiocyanate and urea.