ChEBI

A molecular entity capable of donating a hydron to an acceptor (Bronsted base).

Any eukaryotic metabolite produced during a metabolic reaction in animals that include diverse creatures from sponges, insects to mammals.

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.