PYCRL belongs to the pyrroline-5-carboxylate reductase family. Pyrroline-5-carboxylate reductase catalyzes the the NAD(P)H-dependent conversion of pyrroline-5-carboxylate to proline. Pyrroline-5-carboxylate reductase(P5CR) is the enzyme that catalyzes the terminal step in the biosynthesis of proline from glutamate, the NAD(P) dependent oxidation of 1-pyrroline-5-carboxylate into proline.
Pyrroline-5-carboxylate reductase, which converts pyrroline-5-carboxylate to proline, has been identified in human erythrocytes. The level of pyrroline-5-carboxylate reductase activity in these cells is comparable to the activity levels of major erythrocyte enzymes. The physiologic function of the enzyme in erythrocytes cannot be related to its function in other tissues.