Hi
I have purified protein of interest. The sample was buffer exchanged to 20 mM HEPES pH 6.8, 200 mM NaCl and was concentrated by Amicon Ultra. The protein could be concentrated to at least 0.2 mM. But the precipitation was observed next day. I need at least 0.4 mM for NMR analysis.
The protein pI is 8.0 and MW is 14 kDa. And the sample was concentrated and stored at 4 degree.
Any good idea?
Dear Kiyohiro:
Proteins showing low molecular mass tend to aggregate when the protein concentration of the sample increases. We had the same problem long time ago working with ferredoxin (small Fe-S protein of around 12 kDa). I suggest to concentrate the sample just shortly before NMR analysis. Storage and low temperatures promote this protein aggregation.
Good luck!
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