3-aminobutyryl-CoA aminotransferase that acts specifically on coenzyme A (CoA) esters and catalyzes the conversion of 3-aminobutyryl-CoA into acetoacetyl-CoA in an alternative pathway of lysine fermentation. (3S)-3-aminobutanoyl-CoA + 2-oxoglutarate = acetoacetyl-CoA + L-glutamate kcat is 1.80 sec(-1) for 3-aminobutyryl-CoA. kcat is 1.80 sec(-1) for alpha-ketoglutarate. kcat is 0.4 sec(-1) for pyruvate. Optimum pH is 8.0. Amino-acid degradation; L-lysine degradation via acetate pathway. Homodimer. Belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family.