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 isn't an essential amino acid, which means that humans can synthesize it. It is unique among the 20 protein-forming amino acids because the α-amino group is secondary. Biosynthesis Proline is biosynthetically derived from the amino acid L-glutamate and its immediate precursor is the imino acid (S)-1-pyrroline-5-carboxylate (P5C). Enzymes invo… (More on Proline)