There are several ways of measuring fluxes, however all of these are indirect. Due to this, these methods make one key assumption which is that all fluxes into a given intracellular metabolite pool balance all the fluxes out of the pool.
This assumption means that for a given metabolic network the balances around each metabolite impose a number of constraints on the system.
The techniques currently used mainly revolve around the use of either nuclear magnetic resonance (NMR) or gas chromatography–mass spectrometry (GC–MS).
In order to avoid the complexity of data analysis, a simpler method of estimating flux ratios has recently been developed which is based on cofeeding unlabelled and uniformly C labelled glucose. The metabolic intermediate patterns are then analysed using NMR spectroscopy.
This method can also be used to determine the metabolic network topologies.