Dear Terry,
Is this a test? If you have 8 from the N-terminal that are perfect, and
you only have 2 left over one of which is gly at the C-terminal, there
can only be a problem in the gly and the next C-terminal amino acid. If
the Gly was on the resin when you started synthesis, that narrows it
down to just the 2nd from the C terminal, whatever that was. By adding
up protection groups masses and subtracting that alleged missing amino
acid, if it is missing, might give you an answer.
An amino acid analysis would tell you if you have all 10 amino acids.
But since you sequenced it, I would in the future covalently link your
peptide to an aryl (Millipore) filter. If you go easy on the reagent
when you are covalently linking (I use about 90%), you should see all 10
amino acids even though your Glu, Asp and C-terminal yields would be
low.
Remember, protection groups will come off in the sequencing at various
rates, so no one method is going to tell you all is well. Also, a mass
spec peak is not always THE mass spec peak of your peptide gimish!
Wouldn't it be nice if someone would write a program where you could
put in all your amino acids with protection groups and have the
computer figure all the modifications, omissions and things that could
go wrong and give you the mass units of each? I'm surprised it hasn't
be written yet, or has it?
Cheers, Peggy Rifleman
Terry Stoming wrote:
>
> I ave recently synthesized a peptide with the following aa:
> 2G N and C terminal
> 2S
> 2R
> 1F
> 1T
> 1L
> 1E
> MW 1109.2. The HPLC looks good. Synthesis was in the Perseptive Pioneer. Coupling and deprotection look fine. Mass spec gives a good peak with a mw of 1123.7. I sequenced the peptide on a procise (glass membrane). The sequence died after 8aa which doesnt surprise me. The calls were 100% for the first 8. What do I have? Why is the mw off by 15?
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