The unfolding of hen egg-white lysozyme induced by urea and guanidine hydrochloride (GuHCl) has been studied by "phase diagram" method of fluorescence. In the absence of 2-mercaptoethanol, the conformational transi-tion from the native state to a partially folded intermediate of this protein occurs in the range of urea concentration (0～4.0 mol/L) and GuHGl concentration (0～3.0 mol/L), and the transition from the intermediate to the unfolded state of this protein occurs in the range of urea concentration (4.0～8.0 mol/L) and GuHCl concentration (3.0～6.0 mol/L) , indicating that lysozyme unfolding follows a three-state model under such conditions. In the presence of this reducing agent, however, the denaturation of lysozyme induced by urea obeys a typical two-state model and there is only one conformational transition from the native to the unfolded states during the unfolding. The experimental results show that the "phase diagram" method of fluorescence can be used to detect unfolding intermediates of proteins.

Key words: LYSOZYME, UREA, guanidine hydrochloride, GUANIDINES, FLUORIMETRIC ANALYSIS, PROTEIN, PHASE DIAGRAM