Proline is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group -NH2 but is rather a secondary amine. The secondary amine nitrogen is in the protonated NH2+ form under biological conditions, while the carboxy 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 secondary 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.

Functions of proline include helping form collagen, regenerating cartilage, forming connective tissue, repairing skin damage and wounds, healing the gut lining, and repairing joints.

Proline is obtained through fermentation from a GMO-free corn liquor (glucose, bacteria, water), separation and drying.