One of the 20 amino acids that make up proteins. Its amino group and the 3rd carbon atom of the side chain form a ring.



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Proline (C₅H₉NO₂)


Molar mass: 115.13 g/mol

Melting point: 220 °C (428 °F)

Density: 1.380 g/cm³ (0.0499 lb/in³)


Proline is a non-essential amino acid; it can be produced by the human body. It is a colorless, hygroscopic, crystalline substance, well soluble in water, soluble in alcohol, but insoluble in ether.

Occurrence and production

It is produced by hydrolysis of all proteins. It also occurs in its free state in plants. Collagen and collagen-like proteins contain particularly high amounts of this amino acid. Biosynthesis of proline proceeds from glutamic acid.


Proline is a building block of proteins. It plays an important role in the proper functioning of joints and tendons.

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Amino acids

Amino acids are the monomers of proteins.

Pyrrole (C₄H₅N)

A heterocyclic organic compound.

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