Probing metabolic pathways with isotopic tracers: insights from mammalian metabolic physiology.

Metabolic Engineering offers an opportunity to forge a link between metabolic physiologists, working with mammalian systems and metabolic engineers. Many parallels may be drawn between the specific modification of metabolic networks to improve cellular properties and the analysis of metabolic networks in search of causes of disease. At the core of both fields is the measurement of fluxes. This issue of Metabolic Engineering highlights important topics: mammalian metabolic physiology where estimating fluxes is challenging. The challenges come from compartmentation of metabolites, from dilution of tracer by endogenous pools, and from the difficulty of sampling relevant pools. The common theme across these investigations is the use of isotopic tracers. The wide variety of tracers and tracer analysis techniques in use in mammalian metabolic physiology reflects the complexity of the systems under study. In presenting these examples from the field of mammalian metabolic physiology, our goal is to strengthen the linkages between physiologists and engineers as we develop our knowledge and appreciation of the complexity of metabolic networks.