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. Author manuscript; available in PMC: 2022 Jul 18.
Published in final edited form as: Nat Metab. 2021 Jul 1;3(7):896–908. doi: 10.1038/s42255-021-00419-2

Fig. 4 |. Pre-steady-state versus steady-state measurements of tissue metabolite labelling.

Fig. 4 |

Pre-steady-state (slow) labelling of a metabolite from tracer infusion (bottom) can directly measure the production flux of the metabolite (for example, in protein synthesis or de novo lipogenesis). Steady-state (fast) metabolite labelling (top) does not measure production flux but rather the fraction of metabolite contributed by the circulating tracer nutrient (for example, in glycolysis). Intermediate labelling (middle) can measure both, depending on the time point at which tissues are sampled (for example, in the TCA cycle).