Barbara,
Not that I'm particularly trained in MS (I hope the guru's out there chip in
with a discussion about using isotopic distribution to sort this out) But I
would think that sulfer, being an "A+2" compound (34S = 4.4% of natural
abundance)would allow one to determine the number of sulfurs in isobaric
molecules from the isotopic distribution - if the molecule is not too large.
The Protein Prospector site at UCSF has an isotopic calculator that should
give the predicted envelope. But what's the third peak?
Alan
-----Original Message-----
From: Barbara Ciani
To: Recipients of ABRF List
Sent: 10/27/00 9:43 AM
Subject: MS intra and inter disulfides
Dear all,
I am having big troubles during the oxidation of a peptide with one Cys
at
each of the termini.
The HPLC trace tells me that I have 3 peaks and the Mass-spec says that
all 3 are the same thing: cyclic monomer disulfide linked (also the
distance between the C13 and C12 isotopes is +/- 1 Da as it should be).
My problem is how reliable is the isotope difference rule?
In relation to the mass-spec:If I have dimers should I see a peak
of the correspondent single charged
ion or should I see just the double charged dimer?(that would have the
same ion mass of the monomer?).
In relation to the HPLC: why 3 different peaks for the same thing?
Hope someone can help.
Barbara
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