Hi Katja,
Sodium sulphate forms a solution of neutral pH in water. 200 mM of Na2SO4 will buffer the crystallization solution at pH 7, in addition to acting as a salt. You could try varying the concentration of PEG and Sod.sulphate now to see if the crystals get better. Sometimes using potassium or calcium sulphate instead of Sodium at the same concentration can also yield good results. You could also screen for additives. In my opinion, varying the pH of the protein solution at this stage is not a good idea, as it has already been optimised during purification. regards Ganesh On Thu, 19 Nov 2009 09:33:57 +0000, Katja Schleider wrote: Hi everybody, sorry for my off-topic question. I got small initial crystals in 200mM NaSulfat and 20% PEG 3350. There is no buffer in this condition. How can I optimize these crystals? Just vary the PEG concentration? Or should I add a buffer; or vary the pH of the buffer the proteinsolution was in? Thank you and best regards, Katja
