No abstract

Two acyl-CoA carboxylases from Streptomyces coelicolor have been successfully reconstituted from their purified components. Both complexes shared the same biotinylated ␣ subunit, AccA2. The ␤ and the ⑀ subunits were specific from each of the complexes; thus, for the propionyl-CoA carboxylase complex the ␤ and ⑀ components are PccB and PccE, whereas for the acetyl-CoA carboxylase complex the components are AccB and AccE. The two complexes showed very low activity in the absence of the corresponding ⑀ subunits; addition of PccE or AccE dramatically increased the specific activity of the enzymes. The kinetic properties of the two acyl-CoA carboxylases showed a clear difference in their substrate specificity. The acetyl-CoA carboxylase was able to carboxylate acetyl-, propionyl-, or butyryl-CoA with approximately the same specificity. The propionylCoA carboxylase could not recognize acetyl-CoA as a substrate, whereas the specificity constant for propionyl-CoA was 2-fold higher than for butyryl-CoA. For both enzymes the ⑀ subunits were found to specifically interact with their carboxyltransferase component forming a ␤-⑀ subcomplex; this appears to facilitate the further interaction of these subunits with the ␣ component. The ⑀ subunit has been found genetically linked to several carboxyltransferases of different Streptomyces species; we propose that this subunit reflects a distinctive characteristic of a new group of acyl-CoA carboxylases.The first committed step in the biosynthesis of long-chain fatty acids in all animals, plants, and bacteria is catalyzed by acetyl-CoA carboxylase (ACC) 1 (EC 6.4.1.2) (1). The reaction catalyzed by ACC involves two separate reactions.