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How do scientists trace nutrients through metabolic pathways using isotopes?

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Diagram showing how epinephrine binding to a beta-adrenergic receptor on a cell membrane activates a G-protein, which then stimulates adenylyl cyclase to convert ATP into cyclic AMP (cAMP), leading to physiological effects such as increased heart rate, blood vessel dilation, and glycogen breakdown. — Biochemistry In biochemistry, researchers study the chemical substances and processes that occur in living organisms and cells. In particular, various processes by which cells gain energy, such as epinephrine-stimulated cAMP synthesis, have been deduced through the study of biochemistry.

Scientists trace nutrients through metabolic pathways by using isotopic tracers, which are atoms of an element that have been labeled with either a radioactive or a nonradioactive isotope. Because these isotopes are chemically indistinguishable from the stable forms of the same element, they can be incorporated into biological compounds and participate in normal physiological processes, allowing researchers to follow the fate of a specific nutrient, chemical group, or atom as it moves through a system.1234

To detect these tracers, scientists utilize specialized technology:

Radioactive Detection: If a radioisotope is used, its movement can be tracked by measuring the radiation it emits using devices such as Geiger-Müller counters, scintillation detectors, or gamma-ray spectrometers.14
Mass Spectrometry: For both radioactive and stable isotopes, mass spectrometry is a critical analytical technique. It identifies and quantifies substances by sorting gaseous ions based on their mass-to-charge ratios, enabling researchers to measure the abundance of labeled compounds and identify intermediate species formed during metabolic reactions.536

By administering these labeled nutrients, biochemists can determine distribution patterns, rates of material transport, and the specific enzymatic steps involved in complex metabolic pathways.123