The epsilon amino to imine modification with a gain of 12u offered by Mark
below seems quite feasible.
I have another possibility (or I may be mistaken and it is the same
modification).
On my "Delta Mass" list of modifications
(http://www.medstv.unimelb.edu.au/WWWDOCS/SVIMRdocs/MassSpec/deltamassV2.html) I
include the gain of 13 u as the conversion of lysine to syndesine. This
modification was extracted from the famous Krishna and Wold paper.
I have no idea what syndesine is and wonder of it is related (or the same
as) Mark's modification.
Does anyone have any ideas?
Kindest regards...Ken
>Date: Thu, 30 Jul 1998 08:17:28 -0500
>From: Mark E Hail <hailm@bms.com>
>Subject: Re: MS:bizarre amino acid modification
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>Abrf'ers
>
>If anyone is interested, we found a reference (see below) for the strange
>modification of 12 mass units that I described in my original note. In our
>case it looks like imine formation on a Lys residue.
>
>Mark Hail
>Bristol-Myers Squibb
>Princeton, NJ
>
>
>
>> >L7 ANSWER 1 OF 1 CA COPYRIGHT 1998 ACS
>> >AN 112:62735 CA
>> >TI Characterization of impurities in a synthetic renin substrate
>> > peptide by fast-atom bombardment mass spectrometry and hybrid tandem
>> > mass spectrometry
>> >AU Mathews, W. Rodney; Runge, Thomas A.; Haroldsen, Peter E.; Gaskell,
>> > Simon J.
>> >CS Upjohn Co., Kalamazoo, MI, 49001, USA
>> >SO Rapid Commun. Mass Spectrom. (1989), 3(9), 314-19
>> > CODEN: RCMSEF; ISSN: 0951-4198
>> >DT Journal
>> >LA English
>> >AB Fast-atom bombardment mass spectrometry of a synthetic renin
>> > substrate decapeptide (Pro-His-Pro-Phe-His-Leu-Val-Ile-His-D-Lys)
>> > indicated the presence of several side products, including a
>> > component 12 Da higher in mass. Low-energy collisionally activated
>> > ***decompn*** . analyses were performed using a hybrid tandem
>> > instrument and demonstrated that the heavier side product had two
>> > components, in which the structural modification was either at the
>> > N- or the C-terminus. Addnl. analyses of the N-acetyl deriv.
>> > indicated that for each component the structural modification
>> > blocked a site of N-acetylation. It is suggested that the formation
>> > of these side products is attributable to the generation of
>> > formaldehyde, during removal of the histidine protecting group
>> > (benzyloxymethyl), which reacts with the N-terminus of the peptide
>> > to give an imidazolidinone structure or with the D- ***lysine***
>> > .epsilon.-amine group to yield an ***imine*** . While the
>> > precise genesis of the side-products remains speculative, it is
>> > clear that the combined strategy of derivatization and tandem mass
>> > spectrometry has allowed structural conclusions concerning
>> > individual components of an isobaric mixt.
>> >
>> >
>> >> >All,
>> >> >
>> >> >I have a 3kD peptide with the sequence NH2-Pro-Lys-Lys-yadayadayada. In
>> >> >a forced degradation study, peptide solid was subjected to 40 C/75%
>> >> >humidity for 8 weeks (yikes). The peptide is an acetate salt. MS
>> >> >indicates that the peptide undergoes a mass modification of 12 u. MS/MS
>> >> >fragmentation appears to indicate that "the modification of 12" is on
>> >> >the first lysine. About the only thing that I can come up with that
>> >> >adds 12 is the formation of an immine from the lysine amino group (i.e.,
>> >> >(CH2)4-NH2 --> (CH2)4-N=CH2). Has anyone seen anything like this before
>> >> >or can you suggest alternative explanations? I can't seem to find any
>> >> >reference of this in the usual places. Thanks for your help!
>
********************************
Ken I. Mitchelhill
The John Holt Protein Structure Laboratory
St. Vincent's Institute of Medical Research
41 Victoria Parade
Fitzroy 3065 Victoria
AUSTRALIA
Telephone: 61-3-9288 2480
Facsimile: 61-3-9416 2676
Email: k.mitchelhill@medicine.unimelb.edu.au
Laboratory: http://www.medstv.unimelb.edu.au/WWWDOCS/SVIMRdocs/JHPSL.html
ABRF: http://www.abrf.org
***********************************