Systematic Studies on the Crystallization of Lysozyme

The concentration changes which accompanied the crystal growth of hen egg-white lysozyme from its aqueous solution were followed optically at 5, 10, 15, 30, 42, and 50°C for 30–360 days in the presence of 1–7% NaCl. When the initial protein concentration was selected so as to start the crystallization within a reasonable time and with a proper number of nuclei, the supernatant concentration approached constant values after 1–1.5 month, which were regarded as solubility (S) of the crystals. Phase diagrams representing S as functions of NaCl content and temperature were obtained for two crystal forms of lysozyme. From the Arrhenius plot, the enthalpy of crystallization for the tetragonal form was calculated to be − 72 kJ/mol, and that for the orthorhombic form to be −32 kJ/mol. Conditions necessary for obtaining accurate phase diagrams were discussed, together with their possible use for crystal growth and for future molecular engineering.