PHA synthase PhaC

R. eutropha, formerly known as Alcaligenes eutrophus, has been used for the commercial production of P(3HB-co-3HV) [72]. This bacterium grows well in a relatively inexpensive minimal medium and accumulates a large amount of P(3HB) under the unbalanced growth condition. In R. eutropha, acetyl-CoA is converted to P(3HB) by three enzymes (genes) /J-ketothiolase (phaA), aceto-acetyl-CoA reductase (phaB), and PHA synthase (phaC) [6]. 

In this chapter, we focus on the synthesis of polyhydroxyalkanoic acids (PHA) and cyanophycin (cyanophycin granule polyperptide, CGP) and the key enzymes PHA synthase (PhaC) and cyanophycin synthetase (CphA), respectively. Both polymers are synthesized by template-independent processes. The issue of template dependency and template independency will be illustrated in more detail with polymers consisting of amino acids. 

Saccharomyces cerivisiae is the only eukaryotic organism which has been transformed to acciunulate PHB so far with expression of the PHA synthase (phaC ) of R. eutropha in the S. cerivisiae cytoplasm. In contrast to E. coli and plants, yeast does not reqttire the expression of p-ketothiolase and acetoacetyl-CoA reductase genes for the PHA accrrmulation and these steps are catalyzed by the native ErglO and Fox2 proteins, respectively, which are involved in p-oxidation but functioning as P-ketothiolase and acetoacetyl-Co A reductase (Leaf et al., 1996). 

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