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 kcat is 3.5 sec(-1) for CoA as substrate. kcat is 3.4 sec(-1) for AKP as substrate. Heterodimer with OrtA. Belongs to the threonine synthase family.