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 <cbing...@biochem.wisc.edu> > 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 > > cait...@uchicago.edu >
