Metabolic flux, definition

Enforcing stoichiometric, capacity, and thermodynamic constraints simultaneously leads to the definition of a solution space that contains all feasible steady-state flux vectors. Within this set, one can find a particular steady-state metabolic flux vector that optimizes the network behavior toward achieving one or more goals (e g., maximize or minimize the production of certain metabolites). Mathematically speaking, an objective function has to be defined that needs to be minimized or maximized subject to the imposed constraints. Such optimization problems are typically solved via linear programming techniques. 

Kurata H, Zhao Q, Okuda R, Shimizu K (2007) Integration of enzyme activities into metabolic flux distributions by elementary mode analysis. BMC Syst Biol 1 31 Larhlimi A, Bockmayr A (2009) A New constraint-based description of the steady-state flux cone of metabolic networks. Discret Appl Math 157 2257-2266 Larhlimi A, Blachon S, Selbig J, Nikoloski Z (2011) Robustness of metabolic networks a review of existing definitions. Biosystems 106 1-8... 

The concept of elementary flux modes has resulted in a vast number of applications to analyze and predict the functionality of metabolic networks [64, 65, 138, 241 243]. Software resources that allow for the computation of elementary flux modes are fisted in Table V [178, 224], It should be noted that, due to their definition as an exhaustive enumeration of possible flux distributions,... 

This simple experiment was important in that it clearly established the key notion that cellular extrusion of sodium ions by the sodium pump was coupled to metabolism. Because in this and subsequent experiments of the same sort the electrochemical gradient for sodium was known precisely, and since the fluxes of sodium (and later potassium) both into and out of the cell could be measured independently, this study also laid the groundwork for a theoretical definition of active transport, a theory worked out independently by Ussing in the flux ratio equation for transepithelial active transport of ions (see below). 

Mathematical optimization deals with determining values for a set of unknown variables x, X2, , x , which best satisfy (optimize) some mathematical objective quantified by a scalar function of the unknown variables, F(xi, X2, , xn). The function F is termed the objective function bounds on the variables, along with mathematical dependencies between them, are termed constraints. Constraint-based analysis of metabolic systems requires definition of the constraints acting on biochemical variables (fluxes, concentrations, enzyme activities) and determining appropriate objective functions useful in determining the behavior of metabolic systems. 

In vitro testing is helpful in making definitive or differential diagnoses when the results of acylcarnitine analysis are ambiguous. Such tests can include specific enzyme analysis, flux studies and metabolic substrates used in association with acylcarnitine analysis. These tests can also generally be applied to prenatal specimens, and are of course accessible to laboratories that are equipped with tandem mass spectrometers. 

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