Hello Sreetama: I think for crystallization, everything is hard to say. But if you find your crystal is sensitive to the pH, you certainly can optimize the pH value but it is better not to deviate a lot. For example you can make 0.2 unit interval (for example: pH value 4.5, 4.7, 4.9...etc which are closed to your original pH value ). For the buffer, you can change or not. Another thing is that, you can also incorporate bis-tris in your last purification, since you find your crystal in this buffer. When you do additive screen, the drops which is clear, also can give you important information. You might find a compont which can "inhibit" crystal formation. You can use it to slow down the crystal formation to get a big or single crystal.However, you see, sometimes, this optimization is time consuming. I suggest you to try seeding. It can give you a big surprise, sometimes. Yu Xiaodi
Date: Wed, 8 Feb 2012 11:56:30 +0530 From: [email protected] Subject: [ccp4bb] pH optimisation for crystallisation To: [email protected] Dear all, I have a 17 KDa protein that gives crystals in a condition that has 0.1M bis-tris pH 6.5. The crystals are thin needle clusters and do not diffract. I have tried additives, but they haven't improved the crystals. I intend to vary the pH of the condition. My questions are-1. should the buffer be kept the same or can it also be changed (as long as the desired pH is within the range of both the buffers)?2. in case of a different buffer, should its molarity be the same as that of the original one in the crystallization condition? regards,sreetama
