Metabolic flux is the passage of a metabolite through a given pathway over time. Examining the flow or flux of metabolites through pathways is a leading area of research in metabolism. Macro and microenvironments, hormonal signals and pharmacological perturbations draw unique metabolic flux responses in different cells leading to a diverse range of metabolic phenotypes. These fluxes help elucidate regulation at the level of transcription, translation, post-translation and protein-metabolite interaction. Fluxes are altered under disease conditions such as cardiovascular disease and cancer, so understanding them is of critical value to address treatment efforts. They also provide a look into how microbes are wired informing metabolic engineering as well.

This image from Christian Metallo and Matthew Vander Heiden (see reference 2 below) clearly depicts the similarities between metabolic flux and flow of traffic. The whole network of roads will determine how vehicles move along. If there is a roadblock along point 'A' in the Google Map on the left, then it will lead to slower movement of traffic (red lines) at a given time on certain roads leading to A, and other routes may be available nearby for faster movement of traffic (green lines). Similarly, if you consider the biochemical pathway on the right, decreased flux of AcCoA to citrate at point 'B' could lead to increased flux of aKG to citrate (green arrow). This illustrates how networks whether roads or metabolic pathways are interconnected and changes in flux in one part may be transmitted to other parts, resulting in a global response.