If you find yourself in the situation where the buffer you started with is out
of range of the pH you would
like to attain, there are sets of buffers you can use that contain most of the
standard buffers that will give
you a fairly linear response across ~4-10, as described by Newman, Acta Cryst
D, 2004, v60, pp 610-612.
cheers, tom
________________________________________
From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] On Behalf Of Xiaodi Yu
[uppsala....@hotmail.com]
Sent: Wednesday, February 08, 2012 8:06 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] pH optimisation for crystallisation
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: somon_...@yahoo.co.in
Subject: [ccp4bb] pH optimisation for crystallisation
To: CCP4BB@JISCMAIL.AC.UK
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
