Abstract
The enzyme targets for the rational optimization of a Corynebacterium
glutamicum strain constructed for valine production are identified by
analyzing the control of flux in the valine/leucine pathway. The control
analysis is based on measurements of the intracellular metabolite
concentrations and on a kinetic model of the reactions in the
investigated pathway. Data-driven and model-based methods are used and
evaluated against each other. The approach taken gives a quantitative
evaluation of the flux control and it is demonstrated how the
understanding of flux control is used to reach specific recommendations
for strain optimization. The flux control coefficients (FCCs) with
respect to the valine excretion rate were calculated, and it was found
that the control is distributed mainly between the acetohydroxyacid
synthase enzyme (FCC = 0.32), the branched chain amino acid transaminase
(FCC = 0.27), and the exporting translocase (FCC = 0.43). The
availability of the precursor pyruvate has substantial influence on the
valine flux, whereas the cometabolites are less important as
demonstrated by the calculation of the respective response coefficients.
The model is further used to make in-silico predictions of the change in
valine flux following a change in enzyme level. A doubling of the enzyme
level of valine translocase will result in. an. increase in valine flux
of 31\%. By optimizing the enzyme levels with respect to valine flux it
was found that the valine flux can be increased by a factor 2.5 when the
optimal enzyme levels are implemented. (C) 2009 American Institute of
Chemical Engineers Biotechnol. Prog., 25: 754-762, 2009
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