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. Author manuscript; available in PMC: 2022 Nov 19.
Published in final edited form as: ACS Chem Biol. 2021 Oct 22;16(11):2244–2254. doi: 10.1021/acschembio.1c00379

Figure 6. Proposed mechanism of spontaneous cleavage at Gln and Glu in polypeptides.

Figure 6.

a) The side chain nitrogen atom of Gln attacks the peptide carbonyl on the C-terminal side of Gln. A glutarimide is formed which is accompanied by cleavage of the peptide bond leading ultimately, after hydrolysis, to the formation of a C-terminal Gln. b) The side chain oxygen atom of Glu attacks the peptide carbonyl on the C-terminal side of Gln. A glutaric anhydride is formed accompanied by cleavage of the peptide bond ultimately leading to the formation of a C-terminal Glu residue.