Transaminase that degrades gamma-amino butyric acid (GABA) and uses pyruvate as amino-group acceptor, but not 2-oxoglutarate. 4-aminobutanoate + pyruvate = L-alanine + succinate semialdehyde 4-aminobutanoate + glyoxylate = glycine + succinate semialdehyde Belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family.