Relative effectiveness of various ions on the solubility and crystal growth of lysozyme

Crystallization conditions for hen egg white lysozyme in the presence of various ions were determined at pH 4.5 and 18 degrees C. The corresponding solubility curves show that the main effects are due to anions in the following order: SCN- greater than NO3- greater than Cl- greater than citrate2- greater than CH3COO- approximately H2PO4- greater than SO4(2-). This is in the reverse order of the lyotropic series of Hofmeister. As a consequence, SCN- precipitates and crystallizes lysozyme at low concentration, whereas sulfate is ineffective even at high concentrations. Crystals obtained with each salt were characterized by x-ray diffraction. Lysozyme thiocyanate and nitrate crystals belong to the monoclinic system, whereas all the others have a tetragonal lattice.