I agree with Kara - take off your C-terminal K and you've got your 3680
(monoisotopic)/3683 (ave. MW).
Did you use a resin that was pre-derivatised with K? Are you sure the K was
put on the resin?
Cheers,
Roger
At 04:37 PM 12/7/00 -0500, Kara Pearson wrote:
>Shi-Sheng,
>
>I would guess that your 1227.5+++ peak is monoisotopic, so the MW you
>calculated from that, 3680, is monoisotopic. The MW you calculated for
>residues 1-37, 3683, is the average molecular weight (and what you saw in
>the MALDI). (I get 3684, considering 4 disulfide bridges, close enough)
>The monoisotopic mass for 1-37 is 3681--closer to what you saw in the
>electrospray.
>
>As for the 204 ion in the MS/MS, a few other internal fragments also
>correspond to that mass. (Check out MS-Product at
>http://prospector.ucsf.edu/) I would suggest maybe the C-terminal K isn't
>there.
>
>Kara Pearson
>Post-doctoral Fellow
>NHLBI/NIH
>Bethesda, MD 20892
>301-435-4490
>
>>From: "Shi-Sheng LI" <chembiology00@hotmail.com>
>>To: Recipients of ABRF List <abrf@aecom.yu.edu>
>>Subject: MS & ProtSeq
>>Date: Thu, 07 Dec 2000 18:52:30 -0000
>>
>>Dear Friends:
>>
>>By Edman chemistry, One polypeptide with 38 AA residues follows the sequence
>>as:
>>WSGCSPCPGNECCSKYGYCGLGGDYCGAGCQSGPCYGK
>>It fits quite well with the AAA results. The problem is:
>>1) Maldi MS showed the molecular weight 3684, in the case of ESI Q-tof it's
>>3680, that's ok.
>>2) If we calculate the mw from the sequence above mentioned, we'll get
>>3811 (4 disuphide bridges assumed)
>>So, what's going on with the 131 Da part (3811-3680) during the MS?
>>
>>If the C-terminal K was lost during ionization (? it seems not reasonable?
>>any idea?), probably, the ion with mw 3683 may be observed. But three-charge
>>ion (1227.5) for 3680 was visualized in ESI MS, if K was lost, it should not
>>be able to get three charges, am I right? And also MS/MS on the native
>>peptide (1840.7++) gave reasonable y2 ion 204.14.
>>
>>Any comments are appreciated!
>>
>>
>>Shi-Sheng Li, Ph. D.
>>Biomedical Center, Box 579
>>Uppsala University
>>751 23 Uppsala
>>Sweden
>>Emails: chembiology00@hotmail.com; rockylee86@yahoo.com
>>_____________________________________________________________________________________
>>Get more from the Web. FREE MSN Explorer download : http://explorer.msn.com
>
>_____________________________________________________________________________________
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------------------------------------------------------------
Roger Murphy, Ph.D.
Biological Production Facility
Ludwig Institute for Cancer Research
Austin & Repatriation Medical Centre
Studley Road,
Heidelberg, Vic. 3084
Australia.
Tel 61-3-94965463
Fax 61-3-94965436
Email Roger.Murphy@Ludwig.edu.au
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