Proline

Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group -NH
₂ but is rather a secondary amine. The secondary amine nitrogen is in the protonated form (NH₂⁺) under biological conditions, while the carboxyl group is in the deprotonated −COO⁻ form. The "side chain" from the α carbon connects to the nitrogen forming a pyrrolidine loop, classifying it as a aliphatic amino acid. It is non-essential in humans, meaning the body can synthesize it from the non-essential amino acid L-glutamate. It is encoded by all the codons starting with CC (CCU, CCC, CCA, and CCG).

Proline

ball-and-stick model space-filling model
Names
IUPAC name Proline
Systematic IUPAC name Pyrrolidine-2-carboxylic acid
Identifiers
CAS Number	L: 147-85-3 Y D/L: 609-36-9 Y D: 344-25-2 Y
3D model (JSmol)	L: Interactive image L Zwitterion: Interactive image
Beilstein Reference	80812
ChEBI	L: CHEBI:17203 Y D/L: CHEBI:26271 Y D: CHEBI:16313 Y
ChEMBL	L: ChEMBL72275 Y
ChemSpider	L: 128566 Y D/L: 594 Y D: 8640 Y
DrugBank	L: DB00172 Y
ECHA InfoCard	100.009.264
EC Number	L: 210-189-3
Gmelin Reference	26927
KEGG	L: C00148 Y
MeSH	Proline
PubChem CID	L: 145742 D/L: 614 D: 8988
RTECS number	L: TW3584000
UNII	L: 9DLQ4CIU6V Y D/L: DCS9E77JPQ Y D: L01Q4LGZ5L Y
CompTox Dashboard (EPA)	L: DTXSID9041104
InChI InChI=1S/C5H9NO2/c7-5(8)4-2-1-3-6-4/h4,6H,1-3H2,(H,7,8)/t4-/m0/s1 Y Key: ONIBWKKTOPOVIA-BYPYZUCNSA-N Y D/L: Key: ONIBWKKTOPOVIA-UHFFFAOYSA-N D: Key: ONIBWKKTOPOVIA-SCSAIBSYSA-N
SMILES L: C1C[C@H](NC1)C(=O)O L Zwitterion: [O-]C(=O)[C@H](CCC2)[NH2+]2
Properties
Chemical formula	C5H9NO2
Molar mass	115.132 g·mol−1
Appearance	Transparent crystals
Melting point	205 to 228 °C (401 to 442 °F; 478 to 501 K) (decomposes)
Solubility	1.5g/100g ethanol 19 degC
log P	-0.06
Acidity (pKa)	1.99 (carboxyl), 10.96 (amino)
Supplementary data page
Proline (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Proline is the only proteinogenic amino acid which is a secondary amine, as the nitrogen atom is attached both to the α-carbon and to a chain of three carbons that together form a five-membered ring.