ALDH subfamily of the NAD+-dependent, delta(1)-pyrroline-5-carboxylate dehydrogenases (P5CDH, EC=18.104.22.168). The proline catabolic enzymes, proline dehydrogenase and P5CDH catalyze the two-step oxidation of proline to glutamate. P5CDH catalyzes the oxidation of glutamate semialdehyde, utilizing NAD+ as the electron acceptor. In some bacteria, the two enzymes are fused into the bifunctional flavoenzyme, proline utilization A (PutA). These enzymes play important roles in cellular redox control, superoxide generation, and apoptosis. In certain prokaryotes such as Escherichia coli, PutA is also a transcriptional repressor of the proline utilization genes. Monofunctional enzyme sequences such as those seen in the Bacillus RocA P5CDH are also present in this subfamily as well as the human ALDH4A1 P5CDH and the Drosophila Aldh17 P5CDH.