Hi all,

I am having issues with protein precipitation during buffer exchange. His-tag protein is eluted in 20mM HEPES, 200mM imidazole, 500mM NaCl at pH8.0. During elution, the tube with the highest amount of protein >80uM was cloudy and the remaining tubes with 60uM (1.8mg/ml) were fine! I do not want to concentrate the protein any further as the amount is high enough for my assays. During buffer exchange (20mM HEPES, 100mM salt, pH 8.0) protein started to precipitate. I am wondering if the precipitation is caused by desalting? 

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