Proline

InChI=1S/C5H9NO2/c7-5(8)4-2-1-3-6-4/h4,6H,1-3H2,(H,7,8)/t4-/m0/s1
Key: ONIBWKKTOPOVIA-BYPYZUCNSA-N
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

C₅H₉NO₂Molar mass115.132 g·mol Appearance Transparent crystals Melting point205 to 228 °C (401 to 442 °F; 478 to 501 K) (decomposes) Solubility1.5g/100g ethanol 19 degC log P−0.06 Acidity (pK_a) 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).

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 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.