this outcome depends on the presence of two different 3-ketothiolases in R.eutropha. One, encoded by the phbA gene has a high specificity for acetyl-CoA. the other, encoded by the bktB gene, has a higher specificity for pro-pionyl-CoA.BktB 3-ketothiolase efficiently catalyzes the condensation of propionyl-CoA and acetyl-CoA to form 3-ketovaleryl-CoA. Asingle aceto-acetyl-CoA recuctase(PhbB) catalyzes the reduction of 3-ketovaleryl-CoA