Pyroglutamic acid

Pyroglutamic acid
Names
	Preferred IUPAC name 5-Oxoproline
	Systematic IUPAC name 5-Oxopyrrolidine-2-carboxylic acid
	Other names 2-Pyrrolidone-5-carboxylic acid; Pidolic acid; 5-Oxo-proline;
Identifiers
CAS Number	149-87-1 (R/S) ; 4042-36-8 (R) ; 98-79-3 (S) ;
3D model (JSmol)	Interactive image;
Abbreviations	Glp
Beilstein Reference	82134
ChEBI	CHEBI:16010 (R/S) ; CHEBI:16924 (R); CHEBI:18183 (S);
ChEMBL	ChEMBL284718 ;
ChemSpider	485 (R/S) ; 388752 (R) ; 7127 (S) ;
DrugBank	DB03088 ;
ECHA InfoCard	100.005.227
EC Number	205-748-3;
Gmelin Reference	1473408
IUPHAR/BPS	4703;
KEGG	C02237 ;
MeSH	Pyrrolidonecarboxylic+acid
PubChem CID	499 (R/S); 439685 (R); 7405 (S);
RTECS number	TW3710000;
UNII	6VT1YZM21H (R/S) ; SZB83O1W42 (S) ;
CompTox Dashboard (EPA)	DTXSID80859174 ;
	InChI InChI=1S/C5H7NO3/c7-4-2-1-3(6-4)5(8)9/h3H,1-2H2,(H,6,7)(H,8,9) Key: ODHCTXKNWHHXJC-UHFFFAOYSA-N ; InChI=1S/C5H7NO3/c7-4-2-1-3(6-4)5(8)9/h3H,1-2H2,(H,6,7)(H,8,9)/t3-/m0/s1; InChI=1S/C5H7NO3/c7-4-2-1-3(6-4)5(8)9/h3H,1-2H2,(H,6,7)(H,8,9)/t3-/m0/s1 Key: ODHCTXKNWHHXJC-VKHMYHEASA-N;
	SMILES O=C(O)[C@H]1NC(=O)CC1;
Properties
Chemical formula	C5H7NO3
Molar mass	129.115 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
Related compounds
Related compounds	proline; 2-Pyrrolidone
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Pyroglutamic acid (also known as PCA, 5-oxoproline, pidolic acid) is a ubiquitous but understudied natural amino acid derivative in which the free amino group of glutamic acid or glutamine cyclizes to form a lactam. The names of pyroglutamic acid conjugate base, anion, salts, and esters are pyroglutamate, 5-oxoprolinate, or pidolate.

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, or enzymatically converted by glutaminyl cyclases. This is one of several forms of blocked N-termini 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.

Pyroglutamic acid exists as two distinct enantiomers:

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