Abstract: The unfolding of egg white lysozymes induced by urea and guanidine hydrochloride was studied by using intrinsic fluorescence emission spectra and phase diagram method of fluorescence. The result showed that in these two unfolding procedures, an egg white lysozyme intermediate separately existed at about 4.0 mol/L of urea or 3.0 mol/L of guanidine hydrochloride in denaturation solution, and both of these two unfolding procedures followed a three-state model. Based on the three-state unfolding, an equation which describes the residual activity ratios of egg white lysozymes under different urea and guanidine hydrochloride concentrations in denaturation solution was presented and through this equation two characteristic unfolding parameters, the thermodynamic equilibrium constant k for the conformational transition of protein molecules from their one conformational states to their another ones and the number m of denaturant molecules associated with one protein molecule during the unfolding of protein molecules, can be simultaneously derived. Through using these two characteristic unfolding parameters, we could further describe the distribution and transition of each conformational state of egg white lysozymes under different urea and guanidine hydrochloride concentrations in denaturation solution.

Key words: Egg white lysozyme, Unfolding, Urea, Guanidine hydrochloride, Characteristic unfolding parameter