Journal
JOURNAL OF PROTEOME RESEARCH
Volume 1, Issue 2, Pages 181-187Publisher
AMER CHEMICAL SOC
DOI: 10.1021/pr025503d
Keywords
iodoacetamide; peptide mapping; cyclization; mass spectrometry; S-carbamoylmethylcysteine
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Enzymatic digests of proteins S-alkylated with iodoacetamide may contain peptides with N-terminal S-carbamoylmethylcysteine. These can be partly converted to a form with 17 Da lower mass and increased HPLC retention. Proof by synthesis supported by MS/MS and NMR spectroscopy was used to show that N-terminal S-carbamoylmethyl-L-cysteine can cyclize, losing NH3 to form an N-terminal residue of (R)-5-oxoperhydro-1,4-thiazine-3-carboxylic acid. The abbreviation Otc is proposed for the (R)-5-oxoperhydro-1,4-thiazine-3-carbonyl residue. The rate of cyclization is significant in 0.1 M NH4-HCO3 at 37 degreesC, with the half-life of the acyclic form being 10-12 h for several peptides tested. This is similar to the rate at which N-terminal pyroglutamate forms from N-terminal glutamine.
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