modified L-cysteine residue 4-thiazolidinecarboxylic acid 116.0170135498046875 116.160003662109375 12.0 12.010000228881835938 artifact A protein modification that effectively converts an N-terminal L-cysteine residue by a formadehyde adduct to 4-thiazolidinecarboxylic acid. C 1 thioproline C 4 H 6 N 1 O 1 S 1 PSI-MOD N-term MOD:00965 From DeltaMass: References: Mitchell, M.A., Runge, T.A., Mathews, W.R., Ichhpurani, A.K., Harn, N.K., Dobrowolski, P.J. and Eckenrrrode, F.M. Problems associated with use of the benzylozymethyl protecting group for histidines. Formaldehyde adducts formed during cleavage by hydrogen fluoride. Int. J. Pept. Protein Res. 1990, 36(4), 350-355. Gesquiere, J.-C., Diesis, E. and Tartar, A. Conversion of N-terminal cysteine to thiazolidine carboxylic acid during hydrogen fluoride deprotection of peptides containing pi-N-Bom protected histidine. J. Chem. Soc. Chem. Commun. 1990, (20), 1402-1403. Kumagaye, K.Y., Inui, T., Nakajima, K., Kimura,T. and Sakakibara, S. Suppression of a side reaction associated with Nim-benzyloxymethyl group during synthesis of peptides containing cysteinyl residue at the N-terminus. Pept. Res. 1991, 4(2), 84-87. Colombo, R., Colombo, F. and Jones, J.H. Acid-labile histidine side-chain protection. The N(pi)-t-butoxymethyl group. J. Chem. Soc. Chem. Commun. 1984, (5), 292-293. Notes: Conversion of N-term Cys to thiazolidine during HF deprotection of His(Bom)-containing peptides [1-3]. See structure at http://www.abrf.org/images/misc/dmass12b.gif; modification in red. This modification cannot be excluded during final deprotection/cleavage in Fmoc-chemistry in cases when His(Bum) was employed [4]. For formation of free imino acid see PubMed:1527501. C