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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