Hi Sandy,
If your protein is soluble (i.e. we're not dealing with brown
precipitate), it is possible that the brown color is due to a bound
iron-sulfur cluster. In this case, your protein was always brown, but
you couldn't see the color when it was very dilute. As a quick test,
you could take a UV-Vis spectra. 4Fe-4S clusters have a peak around 410
nm and are distinctly brown in color.
-Andy
===========================================
Andrew T. Torelli Ph.D.
Postdoctoral Associate
Department of Chemistry & Chemical Biology
Baker Laboratory, Cornell University
Ithaca, NY 14853
===========================================
On 9/24/2010 4:34 AM, sandeep 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
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