Dear Deb,Mark,Colin and Ian,
Thank you for your responses and I'm sorry I didn't include
all the pertinent info.
I am doing Fmoc syn, standard Fast fmoc cycles from ABI,
fmoc-arg-pbf. I'm using a 430 that, while ancient by instrumentation
standards, has consistently been reliable. I mentioned that I saw
this once before, actually the same customer,different sequence, but
with the double Arg seq. That time I did Nterm seq. and confirmed
that the extra Arg was at the Arg-Arg sequence.
I guess the hardest thing to explain is why only one extra
Arg? If my reagents and solvents were bad or the Arg-pbf had a
problem, wouldn't I see problems at every cycle and/or every Arg?
Incidently, I rarely do recouples or dbl couples. Fmoc chemistry is
great!
Thank you again.
Sandie
>Sandie
>What type of synthesis are you doing? tboc or FMOC?
>What protecting groups are on your arginines?
>Have you done N-terminal sequence analysis to verify that you do or do not
>have an extra arginine in the sequence?
>Deb McMillen
>Institute of Molecular Biology
>University of Oregon
>Eugene OR
>
>On Wed, 31 Jan 2001, Sandie Smith wrote:
>
> > Dear pepsyn gurus
> >
> > I have just synthesized a peptide: GARRGKGR-NH2. By mass analysis I
> > have two species,one is correct, the other has an extra Arg (+156).
> > The incorrect one is about 70%. There was nothing to indicate an
> > instrumental error. A Kaiser test indicated only that coupling was
> > not as efficient at the RR cycles as the other cycles. This has
> > happened one time before,two to three months ago, again involving a
> > RR sequence. That time I had done a recouple after the first R. I
> > redid the synthesis, without a recouple and got the correct mass
> > only. I put it down to some unknown, never to be explained, problem,
> > with the recouple. Now it's come up again. Please, does anyone have
> > a solution to this puzzle?
> >
> > Thank you,
> > Sandie
> > Sandra S. Smith
> > Research Associate
> > Protein Microanalysis Facility
> > Institute for Cellular and Molecular Biology
> > MBB 1.420
> > University of Texas, Austin, Texas 78712
> >
Sandra S. Smith
Research Associate
Protein Microanalysis Facility
Institute for Cellular and Molecular Biology
MBB 1.420
University of Texas, Austin, Texas 78712
This archive was generated by hypermail 2b29 : Fri Feb 23 2001 - 13:03:34 EST