Geoghegan KF, Hoth LR, Tan DH, Borzilleri KA, Withka JM, Boyd JG. Cyclization of N-terminal S-carbamoylmethylcysteine causing loss of 17 Da from peptides and extra peaks in peptide maps.
J Proteome Res 2002;
1:181-7. [PMID:
12643538 DOI:
10.1021/pr025503d]
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Abstract
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 NH4HCO3 at 37 degrees C, 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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