Pyridoxal phosphate-dependent enzyme that catalyzes transamination between primary amines and alpha-keto acids. Catalyzes the transfer of the amino group from gamma-aminobutyrate (GABA) to alpha-ketoglutarate (KG) to yield succinic semialdehyde (SSA) and glutamate (PubMed:15723541, PubMed:30498244). Thereby functions in a GABA degradation pathway that allows some E.coli strains to utilize GABA as a nitrogen source for growth (PubMed:12446648). Also catalyzes the conversion of 5-aminovalerate to glutarate semialdehyde, as part of a L-lysine degradation pathway that proceeds via cadaverine, glutarate and L-2-hydroxyglutarate (PubMed:30498244). 2-oxoglutarate + 4-aminobutanoate = L-glutamate + succinate semialdehyde 2-oxoglutarate + 5-aminopentanoate = 5-oxopentanoate + L-glutamate kcat is 47.4 sec(-1) with 4-aminobutanoate as substrate (at 25 degrees Celsius and pH 7.8). Amino-acid degradation; 4-aminobutanoate degradation. Amino-acid degradation. Homotetramer. Induced by RpoS in response to multiple stress conditions, including shifts to acidic pH or high osmolarity as well as starvation or stationary phase. Catabolite repression by glucose (repression relieved by GABA) (PubMed:14731280). Makes part of the gabDTPC operon, which is up-regulated by nitrogen limitation (PubMed:12446648). Cells lacking this gene are not able to utilize GABA as a nitrogen source, in contrast to wild-type, but grow normally with arginine, ornithine, putrescine and agmatine (PubMed:12446648). Cells show only 68% of the wild-type GABA aminotransferase activity (PubMed:20639325). Belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family.