Regulating the Molar Fraction of 4-Hydroxybutyrate in Poly(3-Hydroxybutyrate-4-hydroxybutyrate) Biosynthesis by Ralstonia eutropha Using Propionate as a Stimulator

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The regulation of the molar fraction of 4-hydroxybutyrate (4-HB) in the poly(3-hydroxybutyrate-4-hydroxybutyrate)[P(3HB-4HB)] biosynthesis by Ralstonia eutropha (formerly Alcaligenes eutrophus) was attempted by the supplemental addition of propionate. The molar fraction of 4-HB in P(3HB-4HB) was increased significantly from 12.3 to 51.8 mol% by the addition of a small amount of propionate along with γ-butyrolactone commonly used as a precursor for the biosynthesis of P(3HB-4HB). The mechanism of regulation by propionate was investigated by measuring the variation of enzyme activities related to the biosynthesis of P(3HB-RHB) and the level of intermediate metabolite acetyl-CoA. PHB synthase activity was induced significantly by propionate, and the acetyl-CoA concentration also increased significantly due to the additional supply of propionate. The overflowing acetyl-CoA seems to cause an inhibitory effect on the ketolysis reaction catalysing the lysis of 4-hydroxybutyryl-CoA to two molecules of acetyl-CoA ; consequently, the 4-HB fraction available for polymerization increased. Accordingly, the molar fraction of 4-HB in P(3HB-4HB) biosynthesis seems to be regulated by both an increased 4-HB fraction and an activated PHB synthase due to the supplemental addition of propionate as a stimulator.
社団法人日本生物工学会の論文
2000-04-25