Involved in the anaerobic fermentation of lysine. Catalyzes the reversible reaction between 3-keto-5-aminohexanoate (KAH) and acetyl-CoA to form 3-aminobutyryl-CoA and acetoacetate. The reaction involves the deprotonation of KAH, the nucleophilic addition onto acetyl-CoA and the intramolecular transfer of the CoA moiety. (5S)-5-amino-3-oxohexanoate + acetyl-CoA = (3S)-3-aminobutanoyl-CoA + acetoacetate Amino-acid degradation; L-lysine degradation via acetate pathway. Homotetramer. Belongs to the KCE family.