2-oxoglutarate + 4-aminobutanoate = L-glutamate + succinate semialdehyde (S)-3-amino-2-methylpropanoate + 2-oxoglutarate = 2-methyl-3-oxopropanoate + L-glutamate Amino-acid degradation; 4-aminobutanoate degradation. Belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family.