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
>
|