A. eutrophus synthesizes PHB from acetyl-Coa in a pathway involving three enzymes. The first enzyme, 3-ketothiolase, is used to promote the condensation of two acetyl-CoAs into acetoacetyl-CoA. Next, the second enzyme, acetoacetyl-CoA reductase reduces acetoacetyl-CoA to R(-)-3-hydroxybutynl-CoA. Finally, the third enzyme, PHA synthase polymerizes the R(-)-3-hydroxybutyrl-CoA to form PHB.