A Tryptophyl Circular Dichroic Band at 305 mμ of Hen Egg-white Lysozyme*

A tryptophyl circular dichroic (CD) band at 305 mμ with a small negative ellipticity of hen egg-white lysozyme [EC 3.2.1.17] was found at neutral pH values. The effect of pH on this band and the positive band at 295 mμ which had been observed previously was studied. The pH dependence of the both bands could well be interpreted in terms of the interaction of Trp-108 and Glu-35 with a pK value of about 6. Di- and tri-N-acetylglucosamine and glycol chitin greatly enhanced the negative maximum at 305 mμ. α- and β-Methyl glycosides of N-acetylglucosamine (NAG) enhanced this band slightly, while an equilibrium mixture of α- and β-NAG greatly reduced this band. All these reagents, however, enhanced the positive CD maximum at 295 mμ. The negative CD maximum at 305 mμ was also reduced or abolished in the presence of sucrose, ethanol, urea, or guanidine hydrochloride, which had been shown to interact with lysozyme and enhance the positive maximum at 295 mμ. Glucose and KCl had no significant effect on the 305 mμ-band. These results suggest that the tryptophyl CD band at 305 mμ of lysozyme is more useful than that at 295 mμ for differentiating the interaction of various reagents with lysozyme.