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. It can also use beta-alanyl-CoA as substrate. (5S)-5-amino-3-oxohexanoate + acetyl-CoA = (3S)-3-aminobutanoyl-CoA + acetoacetate 3-fold increase in activity by addition of 10 mM 2-mercaptoethanol. Addition of CoCl(2) and to a lesser extent MnCl(2) increase the activity but not MgCl(2). Inhibited by phosphate buffers but not by 5,5'-dithio-2-nitrobenzoic acid. Optimum pH is 6.5-7.0. The half-maximal rate is observed at 5.2 and 8.1. Amino-acid degradation; L-lysine degradation via acetate pathway. Homotetramer. Belongs to the KCE family.