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
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