Metabolite

A metabolite is any small molecule produced during or emitted by metabolism. Metabolites are typically defined as organic molecules with low molecular weight that participate in metabolism but are not polymeric biopolymers. They encompass intermediates of catabolic and anabolic pathways, signaling molecules, and end products of metabolism. Metabolites can be endogenous, produced by the organism itself, or exogenous, arising from the diet, microbiome, or environment. They are present across all life forms and serve as substrates, products, or regulators of enzymatic reactions.

Metabolites are commonly classified as primary (or central) metabolites required for growth, development, and reproduction, such as amino acids, nucleotides, sugars, organic acids, and nucleotides; and secondary (or specialized) metabolites, which are not essential for basic cellular function but confer ecological advantages, such as alkaloids, terpenoids, phenolics, and antibiotics.

Analytical metabolomics studies aim to identify and quantify metabolites in biological samples, using techniques such as mass spectrometry and nuclear magnetic resonance spectroscopy. Metabolite levels reflect the physiological state of cells and organisms, and shifts can indicate disease, environmental responses, or nutritional status. Metabolites are often placed within metabolic pathways to understand fluxes and network structure.

In medicine and biotechnology, metabolites serve as biomarkers and therapeutic targets, and are produced by engineered metabolic pathways in biotechnology. Metabolites can be excreted, stored, or transformed; clinical samples such as blood and urine provide windows into the metabolome, the complete set of metabolites in a biological sample. The study of metabolites and their roles is called metabolomics.