Denaturation of Proteins. V.* N.M.R. Study of the Arginine Residues of Lysozyme

The heat denaturation of lysozyme has been studied by proton magnetic resonance spectroscopy at 220 MHz in water at pH 2.8. At 20°C a broad resonance is observed at 6.8δ due to the arginine NH 2 resonances, which becomes a well defined triple resonance at 40°C, without any change in the rest of the spectrum. This sharpening of the arginine NH 2 resonances is due to their increased mobilities and/or some normalisation of their chemical shifts. It is proposed that the surface structure of lysozyme is loosened at 40°C, without any change in the hydrophobic core and this is considered to be an intermediate phase in its heat denaturation. The heat denatured product at 80°C in D 2 O retains some noncovalent interactions, since further treatment with guanidine deuterochloride or mercaptoethanol causes sharpening of the aromatic region of the spectrum.