1-Pyrroline-5-carboxylic acid (systematic name 3,4-dihydro-2H-pyrrole-2-carboxylic acid^[2]) is a cyclic imino acid. Its conjugate base and anion is 1-pyrroline-5-carboxylate (P5C). In solution, P5C is in spontaneous equilibrium with glutamate-5-semialdhyde (GSA).^[3]

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1-Pyrroline-5-carboxylic acid

Names
Preferred IUPAC name 3,4-Dihydro-2H-pyrrole-2-carboxylic acid
Other names 1-Pyrroline-5-carboxylic acid δ-1-Pyrroline-5-carboxylic acid P5C
Identifiers
CAS Number	2906-39-0 N
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:1372 Y
ChEMBL	ChEMBL1161508 Y
ChemSpider	1159 Y
KEGG	C04322 Y
MeSH	Delta-1-pyrroline-5-carboxylate
PubChem CID	1196
UNII	52TNU46DHL Y
CompTox Dashboard (EPA)	DTXSID00863056
InChI InChI=1S/C5H7NO2/c7-5(8)4-2-1-3-6-4/h3-4H,1-2H2,(H,7,8) Y Key: DWAKNKKXGALPNW-UHFFFAOYSA-N Y InChI=1/C5H7NO2/c7-5(8)4-2-1-3-6-4/h3-4H,1-2H2,(H,7,8) Key: DWAKNKKXGALPNW-UHFFFAOYAB
SMILES C1CC(N=C1)C(=O)O O=C(O)C1/N=C\CC1
Properties
Chemical formula	C5H7NO2
Molar mass	113.115 g/mol
Acidity (pKa)	1.82/6.07[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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The stereoisomer (S)-1-pyrroline-5-carboxylate (also referred to as L-P5C) is an intermediate metabolite in the biosynthesis and degradation of proline and arginine.^[4][5][6]

In prokaryotic proline biosynthesis, GSA is synthesized from γ-glutamyl phosphate by the enzyme γ-glutamyl phosphate reductase. In most eukaryotes, GSA is synthesised from the amino acid glutamate by the bifunctional enzyme 1-pyrroline-5-carboxylate synthase (P5CS). The human P5CS is encoded by the ALDH18A1 gene.^[7][8] The enzyme pyrroline-5-carboxylate reductase converts P5C into proline.

In proline degradation, the enzyme proline dehydrogenase produces P5C from proline, and the enzyme 1-pyrroline-5-carboxylate dehydrogenase converts GSA to glutamate. In many prokaryotes, proline dehydrogenase and P5C dehydrogenase form a bifunctional enzyme that prevents the release of P5C during proline degradation.^[9]

A reciprocal regulation of delta 1-pyrroline-5-carboxylate synthetase (P5CS) and proline dehydrogenase genes controls proline levels during and after osmotic stress in plants proportional to the level of proline.^[10] This allows an optimum level of proline to be produced from reduced nitrogen to control osmotic stress.