Proline (symbol Pro or P) is a proteinogenic amino acid that is used in the biosynthesis of proteins.

It is non-essential in humans, meaning the body can synthesize it from the non-essential amino acid L-glutamate.

Proline is the only proteinogenic amino acid with a secondary amine, in that the alpha-amino group is attached directly to the main chain, making the α carbon a direct substituent of the side chain.

L-Proline is an osmoprotectant and therefore is used in many pharmaceutical, biotechnological applications.

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