Catalyzes the NADP(+) dependent oxidation of succinate semialdehyde to succinate. H2O + NADP(+) + succinate semialdehyde = 2 H(+) + NADPH + succinate Amino-acid degradation; 4-aminobutanoate degradation. Transcriptionally regulated by GabR in the presence of GABA. Up-regulated under low pH conditions and ethanol. Expression from the gabD promoter was induced by growth in the presence of glutamate. Cells lacking this gene are unable to use GABA as sole nitrogen source (PubMed:12123465). No effect on vanillin degradation (PubMed:26658822). Expressed from the major gabT promoter and from an additional gabD promoter. Belongs to the aldehyde dehydrogenase family.