Hi, A few days ago there has been a useful thread of Q & A about a 43 kD protein co-purified with or instead of the desired target protein, in which BB members described their experiences. I'm not sure whether the reference below has been mentioned, but I just came across it. Apparently these people were sufficiently annoyed by this problem of co-purified e. coli proteins and decided to look carefully into it.
Protein Expression and Purification Volume 70, Issue 2, April 2010, Pages 191-195 doi:10.1016/j.pep.2009.10.018 Identification and characterization of native proteins of Escherichia coli BL-21 that display affinity towards Immobilized Metal Affinity Chromatography and Hydrophobic Interaction Chromatography Matrices Neha Tiwari et.al. Available online 1 November 2009 Cheers, Boaz P.S. I marked it as off-topic just because it's not strictly a crystallographic issue, although it is very much on-topic for most of us, as we all know. Boaz Shaanan, Ph.D. Dept. of Life Sciences Ben-Gurion University of the Negev Beer-Sheva 84105 Israel Phone: 972-8-647-2220 ; Fax: 646-1710 Skype: boaz.shaanan
