Irreversible conversion of delta-1-pyrroline-5-carboxylate (P5C), derived either from proline or ornithine, to glutamate. This is a necessary step in the pathway interconnecting the urea and tricarboxylic acid cycles. The preferred substrate is glutamic gamma- semialdehyde, other substrates include succinic, glutaric and adipic semialdehydes. . This is the function of ALDH4A1 (aldehyde dehydrogenase 4 family member A1, Ensembl gene identifier ENSG00000159423).