Structure of lysozyme. IX. The effect of temperature on the conformation of lysozyme

The optical rotatory and ultraviolet spectral studies on lysozyme [EC 3.2.1.17, hen's egg white] in various solutions (1—8) have dem-onstrated the existence of an internal fold which is inaccessible to solvent, other than or-helix and randomly coiled portions. It has been also shown that the internal fold of the lysozyme molecule may have a structure of anti-parallel-j9 configuration, that two of six tryptophan residues are buried in the internal fold, and that the internal fold is stabilized mainly by hydrophobic interactions. In the present communication, the effect of temperature on the optical rotatory proper-ties of lysozyme in various solutions has been studied. The purpose of this study is to con-tribute to the further understanding of the stability of the internal fold and helical part of the lysozyme molecule. The data obtained here show that by increasing the temperature only the internal fold is disrupted and no change occurs in the helical part at high concentrations of organic solvents such as dimethylformamide, alcohols, or dioxane. EXPERIMENTAL Lysozyme was prepared from hen's egg white by the direct crystallization method. It was recrystallized four times and finally lyophilized. Guanidine hydrochloride, 1,3-dimethylurea and acetamide were once recrystallized from methanol