An imino acid is any molecule that contains both imino (>C = NH) and carboxyl (-C(=O)-OH) functional groups. Imino acids are related to amino acids, which contain both amino (-$NH_2$) and carboxyl (-COOH) functional groups. Amino acids containing a secondary amine group (the only proteinogenic amino acid of this type is proline) are sometimes named imino acids, though this usage is disputed by some. Proline is biosynthetically derived from the amino acid L-glutamate and its immediate precursor is the imino acid-(S)-1 -pyrroline-5-carboxylate (P5C).