Fluxomics

Metabolic flux refers to the rate of metabolite conversion in a metabolic network. For a reaction this rate is a function of both enzyme abundance and enzyme activity. Enzyme concentration is itself a function of transcriptional and translational regulation in addition to the stability of the protein. Enzyme activity is affected by the kinetic parameters of the enzyme, the substrate concentrations, the product concentrations, and the effector molecules concentration. The genomic and environmental effects on metabolic flux are what determine healthy or diseased phenotype. == Fluxome ==

Similar to genome, transcriptome, proteome, and metabolome, the fluxome is defined as the complete set of metabolic fluxes in a cell. However, unlike the others the fluxome is a dynamic representation of the phenotype. This is due to the fluxome resulting from the interactions of the metabolome, genome, transcriptome, proteome, post-translational modifications and the environment. == Flux analysis technologies ==

Two important technologies are flux balance analysis (FBA) and 13C-fluxomics. In FBA metabolic fluxes are estimated by first representing the metabolic reactions of a metabolic network in a numerical matrix containing the stoichiometric coefficients of each reaction. The stoichiometric coefficients constrain the system model and are why FBA is only applicable to steady state conditions. the COBRA toolbox, and FASIMU. In 13C-fluxomics, metabolic precursors are enriched with 13C before being introduced to the system. Using an analytical technique such as mass spectrometry or nuclear magnetic resonance spectroscopy the level of incorporation of 13C into metabolites can be measured and with stoichiometry the metabolic fluxes can be estimated. ==Stoichiometric and kinetic paradigms==

A number of different methods, broadly divided into stoichiometric and kinetic paradigms. Within the stoichiometric paradigm, a number of relatively simple linear algebra methods use restricted metabolic networks or genome-scale metabolic network models to perform flux balance analysis and the array of techniques derived from it. These linear equations are useful for steady state conditions. Dynamic methods are not yet usable. On the more experimental side, metabolic flux analysis allows the empirical estimation of reaction rates by stable isotope labelling. Within the kinetic paradigm, kinetic modelling of metabolic networks can be purely theoretical, exploring the potential space of dynamic metabolic fluxes under perturbations away from steady state using formalisms such as biochemical systems theory. Such explorations are most informative when accompanied by empirical measurements of the system under study following actual perturbations, as is the case in metabolic control analysis. ==Constraint based reconstruction and analysis==

Collected methods in fluxomics have been described as "COBRA" methods, for constraint based reconstruction and analysis. A number of software tools and environments have been created for this purpose. Although it can only be measured indirectly, metabolic flux is the critical link between genes, proteins and the observable phenotype. This is due to the fluxome integrating mass-energy, information, and signaling networks. Fluxomics has the potential to provide a quantifiable representation of the effect the environment has on the phenotype because the fluxome describes the genome environment interaction. and systems biology, fluxomic methods are considered a key enabling technology due to their unique position in the ontology of biological processes, allowing genome scale stoichiometric models to act as a framework for the integration of diverse biological datasets. == Examples of use in research ==

One potential application of fluxomic techniques is in drug design. Rama et al. used FBA to study the mycolic acid pathway in Mycobacterium tuberculosis. Mycolic acids are known to be important to M. tuberculosis survival and as such its pathway has been studied extensively. By performing in silico single and double gene deletions many enzymes essential to growth were identified. ==References==