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Cobalt leaching of TALON resin perhaps ? Should be more orange type of color, but it depends on the concentration. In any event if you shoot those crystals run a scan to find out what metal is bound and use it for phasing if you have access to a MAD line. Jürgen On Nov 6, 2011, at 9:56 AM, Adrian Goldman wrote: I agree: light yellow (straw-yellow) proteins often indicate metal-binding - it's typically iron III. Zn salts tend to be colourless, and the Mn-pink is too pale to be visible at protein (mM) concentrations. This can be determined by doing flame-spectroscopy, if you don't mind destroying your protein, or at the beam by scanning the various (first-transition metal) edges - because if it is adventitious metal binding, it's likely to be one of the obvious metals. Adrian On 6 Nov 2011, at 16:49, Artem Evdokimov wrote: When we were working on PheRS we noticed that our protein preps (and crystals) had shades of color: sometimes they were pinkish and sometimes yellowish, or even blueish (and often colorless)! We solved the structure eventually and found a new metal-binding microdomain previously not found in these transferases. The funky colors were caused by the microdomain binding various metals, depending on how those particular fermentations were done and how many purification steps were taken :) In the deposited structure luck of the draw had Zn in the site. It just goes to show that proteins have plenty of tricks left up their metaphorical sleeves. Artem On Sat, Nov 5, 2011 at 11:15 PM, Craig A. Bingman <[log in to unmask]<mailto:[log in to unmask]>> wrote: In another thread, you indicated that there were no identifiable cofactor binding sites in your protein, so we are down to less common situations. Some proteins are spontaneously decorated with pyridoxal on surface lysine residues. In some cases, this has absolutely nothing to do with the enzymatic activity of the protein. On Nov 5, 2011, at 5:02 PM, Caitlyn Claire Yeykal wrote: > Hi -- has anyone had crystals that are colored in regular (unpolarized) light? Mine are yellow, and I'm not aware of anything in the buffer conditions that might cause this. I read online that glutaraldehyde can turn protein crystals a golden color, but as far as I know there isn't any of that in the well. Purified in HBS pH 7.2; crystallized in LiCl/PEG4K/Tris pH 8. Any explanations? > > Thanks! > Caitlyn > > ____________________________________ > Caitlyn C. Yeykal > Mrksich Group/Adams Group > Dept. of Biochemistry, University of Chicago > 929 E. 57th St., Rm 547B > Chicago, IL 60615 > [log in to unmask]<mailto:[log in to unmask]> ...................... Jürgen Bosch Johns Hopkins University Bloomberg School of Public Health Department of Biochemistry & Molecular Biology Johns Hopkins Malaria Research Institute 615 North Wolfe Street, W8708 Baltimore, MD 21205 Office: +1-410-614-4742 Lab: +1-410-614-4894 Fax: +1-410-955-2926 http://web.mac.com/bosch_lab/