1-Pyrroline-5-carboxylic acid
1-Pyrroline-5-carboxylic acid is a cyclic imino acid. Its conjugate base and anion is 1-pyrroline-5-carboxylate. In solution, P5C is in spontaneous equilibrium with glutamate-5-semialdhyde. The stereoisomer -1-pyrroline-5-carboxylate is an intermediate metabolite in the biosynthesis and degradation of proline and arginine.
In prokaryotic proline biosynthesis, GSA is synthesized from by the enzyme . In most eukaryotes, GSA is synthesised from the amino acid glutamate by the bifunctional enzyme . The human P5CS is encoded by the ALDH18A1 gene. The enzyme pyrroline-5-carboxylate reductase converts P5C into proline
In proline degradation, the enzyme proline dehydrogenase produces P5C from proline, and the enzyme 1-pyrroline-5-carboxylate dehydrogenase converts GSA to glutamate. In many prokaryotes, proline dehydrogenase and P5C dehydrogenase form a bifunctional enzyme that prevents the release of P5C during proline degradation. In arginine degradation, the enzyme ornithine-δ-aminotransferase mediates the transamination between ornithine and a 2-oxo acid to form P5C and an L-amino acid. Under specific conditions, P5C may also be used for arginine biosynthesis via the reverse reaction of ornithine-δ-aminotransferase.
