초록
Heterologous expression of polyhydroxyalkanoate (PHA) synthase from Delftia acidovorans DS-17 (PhaC<SUB>Da</SUB>) in Escherichia coli JM109 leads to effective production of high-molecular-weight poly[®-3-hydroxybutyrate] [P(3HB)]. This study examined the effect of PhaC<SUB>Da</SUB> expression on P(3HB) production in E. coli JM109 (Da strain) by comparing with the strain expressing PHA synthase (PhaC<SUB>Re</SUB>) from Ralstonia eutropha (Re strain). First, the kinetic properties of PhaC<SUB>Da</SUB> were investigated. Among the five detergents examined, Triton X-100 remarkably activated PhaC<SUB>Da</SUB>, as well as PhaC<SUB>Re</SUB>. The affinity of PhaC<SUB>Da</SUB> for its substrate was lower than that of PhaC<SUB>Re</SUB>, whereas the maximum reaction rate of PhaC<SUB>Da</SUB> was higher than that of PhaC<SUB>Re</SUB>. However, the kinetic differences were not likely to influence P(3HB) production in the cells. Under conditions of P(3HB) production, the translational levels of monomer-supplying enzymes (PhaA and PhaB) were similar in both the Da and Re strains, whereas PhaC exhibited different expression levels: the abundance of soluble PhaC<SUB>Da</SUB> was lower than that of soluble PhaC<SUB>Re</SUB>. This observation suggests that the production of high-molecular-weight P(3HB) by the Da strain would be attributed to the low amounts of active PhaC<SUB>Da</SUB> in the cells.