I have always wondered what the contribution is from the pH-ing counter-ions, because the buffers are always, e.g., Tris-Cl or Na-HEPES. I have often thought it might be more ideal to screen with TRIS-HEPES as the protein buffer, but probably over the years these counter-ions have fortuitously aided crystallization, so maybe it's not so bad. Also, proteins often have salt in the protein stock as well. Bottom line is that I wonder whether in Cale's case it might have been the Na or the Cl that was the key, and perhaps not the hepes/tris.
Jacob Keller -- ******************************************* Jacob Pearson Keller, PhD Postdoctoral Associate HHMI Janelia Farms Research Campus email: j-kell...@northwestern.edu *******************************************
