In enzymology, pyrroline-5-carboxylate reductase () is an enzyme that catalyzes the chemical reaction
The three substrates of this enzyme are (S)-1-pyrroline-5-carboxylic acid, reduced nicotinamide adenine dinucleotide (NADH), and a proton. Its products are L-proline and oxidised (NAD<sup>+</sup>). Nicotinamide adenine dinucleotide phosphate can be used as an alternative cofactor.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-NH group of donors with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is <small>L</small>-proline:NAD(P)+ 5-oxidoreductase. Other names in common use include proline oxidase, <small>L</small>-proline oxidase, 1-pyrroline-5-carboxylate reductase, NADPH-L-Delta1-pyrroline carboxylic acid reductase, and <small>L</small>-proline-NAD(P)+ 5-oxidoreductase. This enzyme participates in arginine and proline metabolism.
As of late 2007, 5 structures have been solved for this class of enzymes, with PDB accession codes , , , , and .