Yellow or brown tinge is very common especially if you have used sonication to lyse the cells. It helps to wash the cells with buffer or even high salt and spin them down again before lysis. If you want brown then you should see what happens when you work with yeast.
Probably flavins or some other pigment comes out at extremely low concentration.. Maybe you could remove it by gel filtration in high salt (1 or 2M NaCl)? Should not mess up the crystallization though and you probably will not find it (colored molecule) in the electron density maps. Good luck. Ray ________________________________ From: Matthew Bratkowski <mab...@cornell.edu> To: CCP4BB@JISCMAIL.AC.UK Sent: Fri, September 24, 2010 11:38:14 AM Subject: Re: [ccp4bb] protein turns brown It could be caused by iron contamination in one of your buffers. We used to buy glycerol in a metal canister and metal would leach into the glycerol. Because of this, one protein that I worked with would turn yellow, even at relatively low concentrations. I did not have this issue when using glycerol from plastic or glass containers though. Matt On Fri, Sep 24, 2010 at 9:03 AM, Van Den Berg, Bert <lambertus.vandenb...@umassmed.edu> wrote: Maybe you should give us a hint about the identity of your protein (if you dare....;-)). I’m sure there are folks around who may be able to say whether or not your protein is supposed to be brown. You can’t expect too much help if you don’t provide (m)any details. > >Cheers, Bert > > > >On 9/24/10 4:34 AM, "sandeep" <toskgu...@rediffmail.com> wrote: > > >Dear all, >> >>I have purified protein from E.coli. expression system. the protein has been >>purified with three independant columns. Now during concentration step using >>amicon, the protein shows brown colour. what could be the reason. >> >>best regards and Thanks, >>sandy >> >> <http://sigads.rediff.com/RealMedia/ads/click_nx.ads/www.rediffmail.com/signatureline....@middle?> >> >>
