I have crystallized in PEG with citrate at pH 3. If you want to go lower
I would suggest maleate:
effective pH range pKa 25°C buffer
1.2-2.6 1.97 maleate (pK1)
2.2-6.5 3.13 citrate (pK1)
Enrico.
On Mon, 07 Nov 2011 14:15:02 +0100, Craig A. Bingman
<cbing...@biochem.wisc.edu> wrote:
I'm not convinced that you need a conventional buffer at pH 2 or 3. At
pH 2, the hydrogen ion concentration is 10 mM. If you want to use
something else, the second pKa for sulfuric acid is around 2. The first
pKa for phosphoric acid is slightly higher than 2. Lactic acid has a
pKa close to 3. Formic acid has a pKa just under 4. Most of these
numbers were in an appendix in the first chemistry text you ever used.
<wink> These numbers imply pretty strongly that most crystallization
screens emphasizing common salts will require determined modification to
hit these low pH values, because many stabilizing anions in the
Hoffmeister series will be partially or completely protonated at these
pH values. PEG and organic screens will require a smaller hammer to
retrofit.
On Nov 6, 2011, at 11:19 PM, Sam Arnosti wrote:
Hi everyone
I have a protein that is extraordinarily stable at PH=3.0 or even 2.0.
I want to crystallize it in the low PH and compare the differences
between the crystals in regular PH and low PH.
I was wondering how people set up the boxes in low PH, as usual buffers
are mostly less acidic.
Regards
Sam
--
Enrico A. Stura D.Phil. (Oxon) , Tel: 33 (0)1 69 08 4302 Office
Room 19, Bat.152, Tel: 33 (0)1 69 08 9449 Lab
LTMB, SIMOPRO, IBiTec-S, CE Saclay, 91191 Gif-sur-Yvette, FRANCE
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http://www.chem.gla.ac.uk/protein/mirror/stura/index2.html
e-mail: est...@cea.fr Fax: 33 (0)1 69 08 90 71
