title: Cyclization of N-terminal S-carbamoylmethylcysteine causing loss of 17 Da from peptides and extra peaks in peptide maps.
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.
authors.affiliation: Pfizer Global Research and Development, Eastern Point Road, Groton, Connecticut 06340, USA. kieran_f_geoghegan@groton.pfizer.com
authors.forename: Kieran F
authors.initials: KF
authors.lastname: Geoghegan
authors.forename: Lise R
authors.initials: LR
authors.lastname: Hoth
authors.forename: Douglas H
authors.initials: DH
authors.lastname: Tan
authors.forename: Kris A
authors.initials: KA
authors.lastname: Borzilleri
authors.forename: Jane M
authors.initials: JM
authors.lastname: Withka
authors.forename: James G
authors.initials: JG
authors.lastname: Boyd
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000031:analogs & derivatives*; D007460:Iodoacetamide / Q000378:metabolism; D013058:Mass Spectrometry; D010455:Peptides / Q000032:analysis* / Q000378:metabolism; D010456:Peptides, Cyclic / Q000032:analysis / Q000138:chemical synthesis* / Q000378:metabolism
chemical_list: D010455:Peptides; D010456:Peptides, Cyclic; D003545:Cysteine; D007460:Iodoacetamide