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Protein at low PH


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#1 jeejay

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Posted 28 April 2010 - 02:46 AM

Hi all!

I have found strange behavior of my current protein :
a bit about it: His6-tail at N-termini, pI around 6.4 ( theoretical from sequence), Soluble in ordinary buffer: 0.1M Tris pH 8.2, ~250 mM NaCl, 1 mM DTT , 0.01% detergent

But by pH screen I have found that at 0.1M glycine pH 3.0 it solubility raise to 30 mg/ml ( in previous only 10 mg/ml) without any addictive - no salt and even without detergent!
Can someone explain what is happened?

P.S.: If I'll mix protein with conc. 30 mg/ml in 50 mM glycine pH 3.0 with another 100 mM buffer with pH 4.0 protein completely precipitates.

#2 mdfenko

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Posted 28 April 2010 - 05:55 AM

the farther the pH is from the pI the greater the net charge on the protein. at pH 3 your pI 6.4 protein has a strong net positive charge. at pH 8.2 it has a smaller net negative charge.

the low pH may also cause some conformational differences in your protein.

raising the pH with the pH 4 buffer reduces the charge, which may be reducing the solubility.
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