Hi Lei,
Try this: 50-100 mM Arginine in your buffers. Or Glutamic Acid. Or both. -- Lisa A. Nagy, Ph.D. University of Alabama-Birmingham [EMAIL PROTECTED] From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of Zheng, Lei Sent: Wednesday, January 23, 2008 10:51 AM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] problem on protein precipitation Hi ccp4ers, Sorry for this out-topic question: Recently we have a membrane protein expressed, after solubilized with detergent and purified from IMAC, the protein looks beautiful in SEC. However, it completely precipitates after the 2-3 days storage in 4 degree. We supplement 2 mM DTT in the new elute from IMAC, the protein looks happy during weeks at 4 degree. However, it starts to form an invisible aggregate (verified from SEC) during the protein concentration by Centricon. I know this is not uncommon problem for both soluble and membrane proteins and wonder if anyone has any tip and experience to overcome this problem. The protein pI is 8.6, buffer used is pH 7.6. Glycerol is always present during the purification. We do have high salt (500mM) in the buffer. Thank you for you input in advance, Lei
