ChEBI

Any metabolite produced during a metabolic reaction in eukaryotes, the taxon that include members of the fungi, plantae and animalia kingdoms.

A molecular messenger in which the molecule is specifically involved in transmitting information between cells. Such molecules are released from the cell sending the signal, cross over the gap between cells by diffusion, and interact with specific receptors in another cell, triggering a response in that cell by activating a series of enzyme controlled reactions which lead to changes inside the cell.

A small molecule which increases (activator) or decreases (inhibitor) the activity of an (allosteric) enzyme by binding to the enzyme at the regulatory site (which is different from the substrate-binding catalytic site).