Journal
RAPID COMMUNICATIONS IN MASS SPECTROMETRY
Volume 17, Issue 22, Pages 2528-2534Publisher
JOHN WILEY & SONS LTD
DOI: 10.1002/rcm.1236
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Funding
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R01GM059240] Funding Source: NIH RePORTER
- NIGMS NIH HHS [R01 GM059240, GM 59240] Funding Source: Medline
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A transformation analogous to the well-known conversion of an N-terminal glutamine residue to pyroglutamic acid is the cyclization of an N-terminal carboxamidomethylated cysteine residue (the normal product of alkylation with iodoacetamide). This yields 5-oxothiomorpholine-3-carboxylic acid, with the same 17 Da mass loss observed in the Gin reaction. Nineteen tryptic peptides with Cys at the N-terminal were identified for this study, and compared with eight with N-terminal Gin. When examined by MALDI-QqTOF and (off-line HPLC)/MALDI-QqTOF measurements, these were all found to undergo the cyclization reactions. The average degree of degradation during overnight digestion was found to be similar to51 and similar to34% for Cys and Gln, respectively; more detailed information on the time course of the reactions was obtained for the peptides CCTESLVNR and QYYTVFDR. Taking this modification into account while sequencing is likely to increase the probability of protein identification by peptide mass fingerprinting, especially for cysteine-rich proteins. Copyright (C) 2003 John Wiley Sons, Ltd.
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