METABOLISM OF POLY-BETA-HYDROXYBUTYRATE .2. ENZYMATIC SYNTHESIS OF D-(-)-BETA-HYDROXYBUTYRYL COENZYME A BY AN ENOYL HYDRASE FROM RHODOSPIRILLUM RUBRUM

Two enoyl coenzyme A hydrases have been separated from Rhodospirillum rubrum extracts whose combined activity results in the racemization of D-(-)-β-hydroxybutyryl coenzyme A to L-(+)-β-hydroxybutyryl coenzyme A. Both hydrases catalyze the reversible hydration of crotonyl coenzyme A to β-hydroxybutyryl coenzyme A. One of the hydrases is specific for the synthesis of the D-(-) isomer (enoyl coenzyme A hydrase (D)) while the other catalyzes the synthesis of the L-(+) isomer. The following reactions are proposed for the racemization of the D-(-) isomer to the L-(+) isomer: d-(-)-β-hydroxybutyryl coenzyme A → crotonyl coenzyme A → L-(+)-β-hydroxybutyryl coenzyme A. Enoyl coenzyme A hydrase (D) has been purified 680-fold and its properties were studied. The enzyme also hydrates crotonyl thioesters of pantetheine and acyl carrier protein. The following pathway for poly-β-hydroxybutyrate synthesis from acetate by R. rubum is proposed: acetate → acetyl coenzyme A → acetoacetyl coenzyme A → L-(+)-β-hydroxybutyryl coenzyme A → crotonyl coenzyme A → D-(-)-β-hydroxybutyryl coenzyme A → poly-β-hydroxybutyrate. © 1969, American Chemical Society. All rights reserved.