Sorry everyone!!
In my haste to share my information I'm afraid I've been misquoting. It's
actually cysteine which can give a yellow colour and these colour changes
indicate merely a suspicion of the rich presence of a particular amino acid
and are not a definitive diagnostic test.
Sorry,
Derek Bradley
----------
At 21:22 14/03/01 Wednesday, Derek Bradley wrote:
>Daniel,
>
>As I don't have any sample of protein untreated with Coomassie I can't
>answer that for sure, however one explanation that I've been given by
>someone in the business for 20 years is that a high concentration of
>tryptophan in the protein in the gel can cause this effect. If the
>tryptophan is likely to be oxidised this can enhance the effect too.
>
>Apparently proteins unusually rich in other amino acids can cause other
>colours to appear e.g. phenylalanine can give a yellow colour.
>
>Regards,
>
>Derek
>
>----- Original Message -----
>From: Daniel Wellner
>To: Derek Bradley ; Recipients of ABRF List
>Sent: Wednesday, March 14, 2001 5:58 PM
>Subject: Re: Tryptic Digests
>
>
>Hi Derek,
>
>Is it possible that the blue color was due to Coomassie that was
>tightly bound to the protein (perhaps in a colorless form) and released
>during tryptic digestion? Would you get the same effect if you digested
>protein that had never been treated with Coomassie?
>
>Daniel
>
>
>At 7:47 AM -0500 3/14/01, Derek Bradley wrote:
> >Hi everybody,
> >
> >I've just completed a tryptic digest where the addition of the trypsin
> >turned the digestion solution dark blue, I've been told that this sort of
> >reaction can happen where there are particularly high concentrations of
> >certain amino acids - apparently in this case tryptophan. I'm intrigued,
> >can anyone expand on what exactly is going on for me?
> >
> >The gel piece was initially stained with coomassie, I destained it with 40%
> >ethanol in 50mM amm. bicarb. and then washed it with 25mM amm. bicarb.,
> >dehydrated with acetonitrile and then added the trypsin in 25mM amm. bicarb.
> >
> >Thanks,
> >
> >Derek Bradley
> >Dept. of Medicine
> >UCL
>
>
>
>
>Daniel Wellner, Ph.D.
>Department of Biochemistry
>Weill Medical College of Cornell University
>New York, NY 10021
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