In vitro Production of Polyhydroxyalkanoates

PHA can be synthesised using proper catalysts (i.e., zinc- or aluminium-based catalyst) with water as the cocatalyst. This in vitro system has been shown to be possible using the PHA synthases purified from various sources [141, 179-181]. It is possible to produce homopolymers and copolymers containing 3HB, 3HV, 4-hydroxyvalerate and 3-hydroxydecanoate [90]. Multiple-enzyme systems have been developed that can utilise cheaper substrates as well as recycle expensive cofactors such as coenzyme A. Nevertheless, the in vitro systems are still expensive to use in order to produce PHA for applications as commodity plastics. Furthermore, hazardous organic solvents are generally required to achieve high enzymatic activity. Present studies focus on the replacement of these organic solvents with supercritical fluids [182] and ionic liquids [183]. 

However, considering the fact that these systems are free from contaminants such as endotoxins [184], the PHA produced in this manner might be more suitable for applications in the medical field where the cost factor is usually overshadowed by material quality and performance. 

---