Calculation of substrate flux using stable isotopes

摘要: The use of stable isotope tracers to calculate substrate kinetics in humans is favored over the radioactive isotopes because their greater safety and versatility. However, potential complications not met when dealing with are caused by 1) natural occurrence used as a tracer 2) necessity administer an amount that cannot be treated "massless." We therefore found it desirable derive theoretically valid equation for calculating rate appearance, Ra, under steady-state conditions using tracer. This yields results differ from those equations conventionally (endogenous) Ra steady state. Quantitative determination error one these revealed commonly metabolic studies negligible, whereas made other likely quite high encountered situations. Finally, allow proper different definitions isotopic enrichment have arisen practical considerations, we derived above determine appropriate two prevalent definitions.