Oxidoreductase that catalyzes the last step in proline biosynthesis, which corresponds to the reduction of pyrroline-5- carboxylate to L-proline using NAD(P)H (PubMed:16730026, PubMed:19648921, PubMed:23024808, PubMed:28258219). At physiologic concentrations, has higher specific activity in the presence of NADH (PubMed:16730026, PubMed:23024808). Involved in the cellular response to oxidative stress (PubMed:16730026, PubMed:19648921). {ECO:0000269|PubMed:16730026, ECO:0000269|PubMed:19648921, ECO:0000269|PubMed:23024808, ECO:0000269|PubMed:28258219}. This is the function of PYCR1 (pyrroline-5-carboxylate reductase 1, Ensembl gene identifier ENSG00000183010).