Interaction of Urea and Guanidine Hydrochloride with Lysozyme*

Abstract

The effects of urea and guanidine hydrochloride (GuHCl) on the circular dichroism (CD) and ultraviolet absorption spectrum of hen egg-white lysozyme [EC 3. 2.1.17] were studied. Urea and GuHCl enhanced the aromatic CD bands of lysozyme in a nondenaturing concentration range. By analyzing the increase in the CD bands with increasing concentration of urea or GuHCl, it was found that one mole of urea or GuHCl interacts with one mole of lysozyme. The difference absorption spectra of lysozyme produced by urea were also interpreted in terms of urea-lysozyme interaction. On the basis of these facts, the tryptophyl exposure of the lysozyme molecule was discussed.