Protein crystallization: scaling of charge and salt concentration in lysozyme solutions

We studied the crystallization of lysozyme solutions by adding sodium chlor ide at pH = 4.5, 5.9 and 7.8. A universal crystallization boundary is found if data are scaled according to the salt concentration normalized by the s quare of the charge at the appropriate pH. Calculations show that this find ing is consistent with recent attempts to rationalize protein crystallizati on using second virial coefficients.