What is Metabolic Flux?
Metabolic flux refers to the rate at which metabolites flow through a metabolic pathway in a cell. It’s typically measured in units like mmol/gDW/hr (millimoles per gram of dry cell weight per hour) and tells us how active a particular pathway is under given conditions.
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Key properties:
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Fluxes describe the functional state of a cell’s metabolism.
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They are dynamic, depending on nutrient availability, genetic makeup, and environment.
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Not all pathways that exist in the genome are active at once; flux tells you which ones are being used, and how much.
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The Relationship With Genome-Scale Flux Models (GSMMs)
GSMMs are computational representations of the metabolic network of an organism, built from genome annotation and biochemical data. They contain:
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A list of all known metabolic reactions the organism can carry out.
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A stoichiometric matrix describing the mass balance of those reactions.
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Constraints like reaction directionality and uptake rates.
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Often analyzed using techniques like Flux Balance Analysis (FBA).
Important: GSMMs predict potential fluxes based on assumptions (e.g., optimizing for growth), but they are not actual measurements of flux.
Are They the Same?
No — but they’re related.
| Concept | Metabolic Flux | Genome-Scale Flux Models |
|---|---|---|
| Definition | Actual rates of metabolite flow | Predictive model of all possible fluxes |
| Data Type | Experimental/empirical | Computational/theoretical |
| Scale | Pathway- or network-level (active) | Whole genome (potential) |
| Use | Analyze physiology under specific conditions | Predict phenotypes, engineer pathways |
How They Work Together
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GSMMs predict fluxes under different scenarios (e.g., knockout strains, different media).
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Flux data (e.g., from ¹³C-labeling experiments) can be used to validate or refine GSMMs.
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Together, they help guide metabolic engineering, drug discovery, and understanding of cell physiology.
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