Proline (abbreviated as
Pro or
P) is an α-
amino acid, one of the twenty
DNA-encoded amino acids. Its
codons are CCU, CCC, CCA, and CCG. It is not an
essential amino acid, which means that the human body can synthesize it. It is unique among the 20 protein-forming amino acids in that the amine nitrogen is bound to not one but two alkyl groups, thus making it a
secondary amine. The more common L form has
S stereochemistry.