A bit behind on reviewing the list but may be of some help.
An identical phenomenon of wrongly identifying pyridylethylated
cystein as
Trp was done in the case the conotoxins PNIV (see Fainzilber et
al, (1995)
Biochem., 34, 8649-56). We mistakenly determined the N terminus
(CCKYG...)
as WCKYG... Only with elaborate MS studies we were able to
correct the
Edman result.
It would be interesting to know if your sequence, too, consists
of two
cysteins in a row in the N-terminus? Additionally, would any one
of you
chemists conjecture what is the molecular species formed from the
N-terminal PEC that gives rise to mock Trp identification?
Dr. Ariel Gaathon
Bletterman Laboratory Research Laboratory for Macromolecules
Interdepartmental Equipment Unit
The Hebrew University Medical School
Jerusalem, P. O. Box 12272, ISRAEL 91120
Tel. (+972)26758489, Fax. (+972)26414069
On Mon, 1 Mar 1999 swiderek@zgi.com wrote:
> Dear Colleagues,
>
> can anybody think of reason why an N-terminal cysteine looks like a tryptophane
> during N-terminal sequence analysis?
>
> We are expecting a Cys in the first cycle but we see a blank (that would match
> the Cys suspicion) or a Trp upon reduction alone or upon reduction & alkylation
> (using 4-VP). A Cys residue a little down the sequence comes out as expected as
> pyridylethylcysteine residue indicating that the chemical reaction worked fine.
> Asking the same question from a different angle: how does an oxidized Trp
> behave on the sequencer?
>
> Thanks for all your help, Kristine
>
>
> Kristine Swiderek
> Assoc. Research Director, Biological Structure
> ZymoGenetics, Inc.
> 1201 Eastlake Ave. E
> Seattle, WA 98102
> Phone: (206)515-4901
> Fax: (206)442-6608
> e-mail: swiderek@zgi.com
>
>