Marcus,
the Delta Mass list on the ABRF web page
http://abrf.org/ABRF/ResearchCommittees/deltamass/deltamass.html
lists 76 as the molecular weight increase with a beta mercaptoethanol
adduct can you get adduction of the cysteine with the
N-methylmercaptoacetamide?
Deb McMillen
Institute of Molecular Biology
University of Oregon
Eugene OR 97403
On Fri, 28 Jul 2000, Marcus Macht wrote:
> Dear all,
>
> at first, thanks to all who sent me their hints and comments about the
> reduction of Met-O. I finally decided to use N-methylmercaptoacetamide (pH
> 8, 100 mM NH4HCO3, peptide conc. 5mg/ml and reduction over 72h, well,
> actually over the weekend...) and it worked fine in two cases where I
> observed Met-O. In the case of the peptide for which I originally asked, it
> didn't. In MALDI-MS I observed a modification with a mass shift 75.1 Da,
> which is stable to the reduction with DTT (the mass shift is observed only
> by one modification at the N-Terminus and the Met-O was properly reduced;
> this was checked by MALDI-PSD). The peptide contains an additional cystein
> which is the place of modification (I actually don't know wether the
> N-terminus or the side chain is modified, but I assume the latter one). Is
> anybody of you aware about the nature of this modification? All
> possibilities I calculated don't make very much sense (e.g. cleavage of the
> amide bond in the acetamide etc.).
> Please dont' worry if you can't figure out since this a merely academic
> question (we have resynthesized the peptide and cleaved it of with 94% TFA,
> 2.5% water, 2.5% TES and 1% EDT; it smells awful, but it avoids oxidation...)
>
> Yours sincerely,
> Marcus
> ********************************************************
> Dr. Marcus Macht
> Universit”t K–ln
> Zentrum f¸r molekulare Medizin
> Zentrales Servicelabor
> Joseph-Stelzmann-Str. 52
> 50931 Koeln
> Tel.: +49 221 478-6995
> Fax: +49 221 478-6977
> e-mail: Marcus.Macht@uni-koeln.de
> ********************************************************
>
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