# Team:TU Delft/Modeling/MFA/explanation

(Difference between revisions)
 Revision as of 08:55, 7 October 2010 (view source) (→Metabolic Flux Analysis, how does it work)← Older edit Revision as of 09:10, 7 October 2010 (view source) (→Metabolic Flux Analysis, how does it work)Newer edit → Line 27: Line 27: Steady-state assumption Steady-state assumption - In order to determine the intracellular rates, it is assumed that all the intermediates inside the cell are in a steady-state. This means that the amount of the substance is constant, meaning that the total production and the total consumption of a substance are equal to each other. For figure 1 this would mean that, if it is known that 1 mmol gx^-1 h^-1 of glucose is going in and 0.8 mmol gx^-1 h^-1 of CO2 is coming out, then the other rates can be calculated. The calculation results in 0.44 mmol gx^-1 h^-1 of ethanol coming out and 0.36 mmol gx-1 h-1 goes through intermediate 2 to the biomass. This is essentially the metabolic flux analysis. For larger networks, however it is required to used lineair algebra or tools such as Cell Net Analyzer. + In order to determine the intracellular rates, it is assumed that all the intermediates inside the cell are in a steady-state. This means that the amount of the substance is constant, meaning that the total production and the total consumption of a substance are equal to each other. This holds also for co-factors such as ATP and NADH which are used by many reactions. This means that all the rates need to have a ratio that balances out the co-factor production and consumption. + + For figure 1 this would mean that, if it is known that 1 mmol gx^-1 h^-1 of glucose is going in and 1.2 mmol gx^-1 h^-1 of CO2 is coming out, then the other rates can be calculated. The calculation results in 1.32 mmol gx^-1 h^-1 of ethanol coming out and 0.36 mmol gx-1 h-1 goes through intermediate 2 to the biomass. This is essentially the metabolic flux analysis. For larger networks, however it is required to used lineair algebra or tools such as Cell Net Analyzer.

# Metabolic Flux Analysis, how does it work

Metabolic flux analysis (MFA) is a tool to study networks quantitatively. It can be used to calculate theoretical maximal yields. For the metabolic flux analysis CellNetAnalyzer, a tool for Matlab, was used. CellNetAnalyzer already has a simplified, yet still extensive metabolic network of E. coli. To this network the hydrocarbon degradation pathway was added. After this, further pathways were added to the network see how efficient certain products could be produced and alternative electron acceptor was investigated.

Metabolic networks - definition

A metabolic network is the collection of all the reactions that occur inside a cell. All these reactions are coupled and form a network together. This network has a couple of transport reactions with substrate (food, such as sugar and alkanes) as an input and products (such as biomass, CO2, ethanol) as output. Other products of the metabolic network are energy, which is stored in molecules such as ATP and NADH, and building blocks for the cell (biomass). The substances between the substrates and the products are called intermediates. An example of this is in figure 1.

Figure 1: Small made-up metabolic network

The change in the concentration of the substrate and products outside the cell can easily be calculated from measurements. This results in uptake and excretion speeds. The intracellelular rates (inside the cell) can not be figured out as easily, but if enough information is known from the uptake en excretion rates, the intracellular rates can often be calculated.

Units in MFA

The term 'rate' has occured in the previous alinea and needs to be specified further. Rates indicate how fast a reaction goes. Rates are usually defined in moles per amount of biomass per time. In CellNetAnalyzer the units 'mmol per gram of dry weight biomass per hour' were used. The reaction that genereates biomass, called μ, is an exception and has the unit per hour, which is derived from biomass produced per biomass per hour.

A metabolic flux analysis does not calculate maximal reaction speeds however! It can only investigates relations between reactions.