PYCRL belongs to the pyrroline-5-carboxylate reductase family and functions as a homodecamer. It may play a critical role in proline bio-synthesis. Proline functions as a non-enzymatic antioxidant to minimize damage caused by reactive oxygen species (ROS) in microorganisms, animals and plants. In the last step of proline biosynthesis, PYCRL catalyzes the reduction of aldehyde dehydrogenase 4A1 (ALDH4A1) to proline using NAD(P)H as the cofactor. Recombinant human PYCRL protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.