Poly-β-hydroxybutyrate is synthesized from acetyl coenzyme A
(acetylcoA) via three enzymatic reactions. 3-Ketothiolase converts
two acetyl-coA molecules to one acetoacetyl-coA molecule, NADPH
dependent acetoacetyl–coAreductase converts acetoacetylcoA to
D-3-hydroxybutyrylcoA and the last enzyme PHB synthase catalyzes
linking of the D-3-hydroxybutyryl moiety to an existing PHB molecule
viaanester bond shown in the Fig. 1.