Pyroglutamic acid

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Pyroglutamic acid[1]
IUPAC name 5-oxopyrrolidine-2-carboxylic acid
Other names Pyrrolidonecarboxylic Acid, Pidolic acid, Pyroglutamate, 5-oxoproline
CAS number 98-79-3
PubChem 499
Molecular formula C5H7NO3
Molar mass 129.114
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Pyroglutamic acid, or pidolic acid, is an uncommon amino acid derivative in which the free amino group of glutamic acid cyclizes to form a lactam. It is found in many proteins including bacteriorhodopsin. N-terminal glutamine residues can spontaneously cyclize to become pyroglutamate. This is one of several forms of blocked N-terminals which present a problem for N-terminal sequencing using Edman chemistry, which requires a free primary amino group not present in pyroglutamic acid. The enzyme pyroglutamate aminopeptidase can restore a free N-terminus by cleaving off the pyroglutamate residue.[2]


  1. Merck Index, 11th Edition, 8012.
  2. Podell DN, Abraham GN (March 15, 1978). "A technique for the removal of pyroglutamic acid from the amino terminus of proteins using calf liver pyroglutamate amino peptidase". Biochem. Biophys. Res. Commun. 81 (1): 176–85. PMID 26343. doi:doi:10.1016/0006-291X(78)91646-7 .