Limitations in Metabolic Engineering Due to Network Rigidity,Glycolysis,TCA Cycle,Pentose Phosphate Pathway,Nodes,Metabolic Rigidity,Nodal Rigidity

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Metabolic Engineering and Metabolomics Metabolic Engineering and Metabolomics Introduction Cloning and Expression of Heterologous Genes Completion of Partial Pathways giving new Products Transfer of an Entire Biosynthetic Pathway Creating new Products and new Reactants Altering Nutrient uptake and Metabolite Transfer of Promising Natural Motifs Redirecting Metabolite Flow Desensitizing Feedback Inhibition Increased Threonine in Bacteria Increased Lysine Content in Crop Plants Elevation of the Activity of rate Limiting Enzymes Alteration in Protein Processing Pathway Reduction of Competition for Limited Resources Modification of Metabolic Regulation Molecular Breeding of Biosynthetic Pathways

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Limitations in Metabolic Engineering Due to Network Rigidity
During metabolic engineering involving primary metabolism (e.g. glycolysis, TCA cycle and pentose phosphate pathway, etc.), the carbon flux distributions at key branch points (called ‘nodes’) is often radically redirected from the flux distributions that are normally associated with balanced growth. Such flux alterations are often directly opposed by mechanisms that have evolved to maintain original flux distributions for optimal growth. This opposition to flux alterations at key branch points or nodes is often described as metabolic rigidity or nodal rigidity. There are relatively few examples where this nodal rigidity has been overcome through genetic manipulations leading to successful flux alterations.

The concept of metabolic or network rigidity can be illustrated using the example of overproduction of lysine by Corynebacterium glutamicum. The metabolic flux distributions (using glucose as a substrate) for balanced growth, for 30-40% molar yield and for maximum yield (75% molar yield) are shown in, where glucose uptake was used as a standard indicated by 100 units. It will be seen that flux distribution for maximum overproduction represents a significant deviation from that for balanced growth or from that for 30-40% overproduction.

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If pathways leading to production of by-products {e.g. pyruvate dehydrogenase complex (PDC) leading to TCA cycle} are blocked, one would expect a shift in metabolic pathway leading to maximum overproduction of lysine. But the metabolic network does not respond to such alterations in metabolic network due to metabolic rigidity at key branch-point or nodes. Such metabolic rigidity must be identified and overcome before results of metabolic engineering can be exploited.

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Carotenoid Biosynthesis Biosynthesis of Novel Carotenoids Biosynthesis of Acyclic and Cyclic Carotenoids Metabolic Engineering for PHAs Metabolic Engineering for Alkaloid Biosynthesis Pathway Analysis for Metabolic Engineering Metabolic Control Analysis (MCA) for Metabolic Engineering Metabolomics and Metabolic Engineering MS,NMR and Metabolomic Profiling Metabolomic Control Analysis and FANCY Limitations in Metabolic Engineering Due to Technology Metabolic Control Theory and Metabolic Engineering Limitations in Metabolic Engineering Due to Network Rigidity Identification and Classification of Principal Nodes Assessment of Nodal Rigidity and its Response to Metabolic Engineering