Pyroglutamic acid

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Pyroglutamic acid
Stereo structural formula of (2S)-pyroglutamic acid
Abbreviations Glp
CAS number 98-79-3 (2S) YesY, 4042-36-8 (2R), 149-87-1 N
PubChem 7405 (2S), 439685 (2R), 499, 10534703 (2S)(3,4-3H2)
ChemSpider 7127 (2S) YesY, 388752 (2R) YesY, 485 YesY, 8710094 (2S)(3,4-3H2) YesY
EC number 205-748-3
DrugBank DB03088
KEGG C02237 N
MeSH Pyrrolidonecarboxylic+acid
RTECS number TW3710000
3DMet B01549
Jmol-3D images Image 1
Molecular formula C5H7NO3
Molar mass 129.11 g mol−1
Melting point 184 °C (363 °F; 457 K)
log P -0.89
Acidity (pKa) -1.76, 3.48, 12.76
Basicity (pKb) 15.76, 10.52, 1.24
Isoelectric point 0.94
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Pyroglutamic acid (also known as PCA, 5-oxoproline, pidolic acid, or pyroglutamate for its basic form) is an uncommon amino acid derivative in which the free amino group of glutamic acid or glutamine cyclizes to form a lactam. It is a metabolite in the glutathione cycle that is converted to glutamate by 5-oxoprolinase. Pyroglutamate is found in many proteins including bacteriorhodopsin. N-terminal glutamic acid and 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.[1]

Pyroglutamic acid, also known as pidolic acid, exists as two distinct enantiomers:

  • (2R) or D which happens to be (+) or d
  • (2S) or L which happens to be (–) or l


The sodium salt of pyroglutamic acid – known either as sodium pyroglutamate, sodium PCA, or sodium pidolate – is used on the skin to retain moisture.[citation needed]

Pyroglutamic acid is sold as a dietary supplement in the United States.[citation needed]

Magnesium pidolate, the magnesium salt of pyroglutamic acid, is a mineral supplement.


  1. ^ Podell, David N.; Abraham, George N. (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, doi:10.1016/0006-291X(78)91646-7, PMID 26343 .