Involved in the ornithine fermentation pathway. Catalyzes the thiolytic cleavage of 2-amino-4-ketopentanoate (AKP) with coenzyme A (CoA) to form acetyl-CoA and alanine. It is strictly specific for AKP. acetyl-CoA + D-alanine = (2R)-2-amino-4-oxopentanoate + CoA Completely inhibited by p-chloromercuribenzoate (p-ClHgBzO) and acetyl-CoA, and partially inhibited by N-ethylmaleimide. Heterodimer with OrtA. Belongs to the threonine synthase family.