Enzyme-catalyzed poly(3-hydroxybutyrate) synthesis from acetate with CoA recycling and NADPH regeneration in Vitro

We established a novel enzyme-catalyzed poly(3-hydroxybutyrate) [P(3HB)] synthesis system capable of recycling CoA on the basis of the P(3HB) biosynthetic pathway in Ralstonia eutropha. The system includes purified beta-ketothiolase (PhaA), NADPH-dependent acetoacetyl-CoA reductase (PhaB), PHA synthase (PhaC), acetyl-CoA synthetase (Acs) and glucose dehydrogenase (GDH). In this system, acetyl-CoA was synthesized from acetate and CoA by Acs and ATP, and then two molecules of acetyl-CoA were condensed by PhaA to synthesize acetoacetyl-CoA, which was converted to (R)-3-hydroxybutyryl-CoA (3HBCoA) by PhaB and NADPH. The 3HBCoA was polymerized by PhaC and converted to P(3HB). In this system, the CoA molecules that were released during the condensation and polymerization reactions catalyzed by PhaA and PhaC, respectively, were reused successfully for the synthesis of acetyl-CoA. In addition, NADPH, which was consumed in the reduction of acetoacetyl-CoA, was regenerated by the action of GDH. In this system, the yield of P(3HB) synthesized from acetate as the substrate was 5.6 mg in a 5-ml reaction mixture, and the weight-average molecular weight and polydispersity were 6.64 x 10(6) and 1.36, respectively. Furthermore, CoA was reused at least 26 times, and NADPH was also regenerated at least 26 times during 24 h of reaction.