catabolite

A catabolite is a metabolite produced during catabolism, the set of biochemical reactions that break down larger molecules to extract energy and reducing equivalents. Catabolic reactions generate substrates that feed into energy-producing pathways and provide building blocks for other cellular processes.

In metabolism, catabolites include intermediates and end products such as pyruvate, acetyl-CoA, lactate, acetate, and various TCA cycle intermediates. These compounds may be further metabolized for energy, used as substrates for biosynthetic pathways, or excreted. The specific catabolites a cell accumulates depend on the available nutrients and the organism’s metabolic state.

Regulation commonly involves catabolites acting as signals that coordinate the use of nutrients. A prominent example is catabolite repression in bacteria, where the presence of a preferred carbon source (typically glucose) suppresses the utilization of other substrates. This regulation often hinges on changes in levels of signaling molecules like cyclic AMP and the activity of transcription factors (for example, CRP or CAP) that control operons for alternative carbon sources. When glucose is scarce, higher signaling activity induces enzymes to metabolize other carbon sources; when glucose is abundant, repression is relieved.

Similar regulatory strategies occur in yeast and other organisms, where preferred carbon sources suppress pathways for less favorable ones. Catabolites thus serve dual roles: as actual metabolic intermediates in energy production and as regulators that optimize nutrient usage across environments.