Hi Matt, I sometimes see a similar thing with my proteins, which definitely don't possess metal co-factors or prosthetic groups. I found that gel filtration got rid of it - the browny-yellow stuff came out in the void fraction so I figured it was aggregated protein. I think it was aggregation via the his-tags around traces of copper in my sample, which could explain the brown-ish colour. What happens if you concentrate the protein in the presence of EDTA? Joe
> Hello. > > I am working with a protein that turns a yellowish-brown color when it is > concentrated to around 2 mg/ml or higher in a small volume (a few hundred > uL). I was wondering if the protein bound a metal or other prosthetic > group that would give it this color? The protein's color somewhat > resembles iron binding proteins, but there is no peak in the 400 nm range > that would suggest heme, and an iron sulfur cluster is not that likely > since there are only five cysteines in the protein. Proteins with > structures homologous to the one I am studying bind magnesium, but are not > know to bind other metals. Any information about what this color might > suggest about the protein or how I could analyze possible bound metals or > prosthetic groups using only a small amount of protein would be helpful. > > Matt >
