METABOLIC FLUX ANALYSIS FOR BIOSYNTHESIS OF POLY(BETA-HYDROXYBUTYRIC ACID) IN ALCALIGENES-EUTROPHUS FROM VARIOUS CARBON-SOURCES

Using the available biochemical information, metabolic networks have b een constructed to describe the biochemistry of synthesis of poly-beta -hydroxybutyrate (PHB) in Alcaligenes eutrophus on a variety of carbon substrates. A metabolic flux analysis of PHB biosynthesis under nitro gen limited conditions was made using butyrate, lactate and acetate as carbon sources. Although the substrates share most metabolic pathways , their flux distributions are quite different. In the case with butyr ate as the carbon source, a nearly constant flux of TCA cycle through isocitrate dehydrogenase under both balanced growth and nitrogen limit ing conditions was obtained from the flux computation. The carbon flow was determined to proceed alternatively through the glyoxylate pathwa y or the PHB synthetic pathway according to the availability of a nitr ogen source. A block in the amino acid synthetic pathway may result in the overproduction of NADPH and accelerate the biosynthesis of PHB. F lux ratios allow a comparison of the effects of carbon sources on PHB synthesis. The results demonstrate that butyrate is more efficient tha n acetate and lactate for PHB production from an energetic point of vi ew. The metabolic networks constructed were also applied to perform a theoretical analysis on the overproduction of PHB. The results indicat e that the maximum PHB yield may be limited by the available NADPH.