THERMODYNAMICS OF DENATURATION OF LYSOZYME BY GUANIDINE HYDROCHLORIDE .I. DEPENDENCE ON PH AT 25 DEGREES

The denaturation of hen egg-white lysozyme has been studied at 25°, as a function of the concentration of guanidine hydrochloride and of the pH. The results of this study show that the pH dependence between pH 1 and 4 is primarily due to two acidic groups that have abnormally low pK’s in the native state. The known three-dimensional structure of the protein, together with literature data on the effects of pH on saccharide binding, suggest that the two groups may be glutamic acid residue 7 and aspartic acid residue 52 or 103. To account for the pH dependence between the pH range covered by this study and earlier data at pH 5.5 requires the presence of additional abnormal acidic groups in the native protein, one of these being the carboxyl group at residue 35, which has been suggested as having an abnormally high pK on the basis of studies of saccharide binding and enzyme kinetics of lysozyme. © 1969, American Chemical Society. All rights reserved.