Toxin

A toxin is a naturally occurringpoison produced by metabolic activities of livingcells or organisms. They occur especially as proteins, often conjugated. The term was first used by organic chemistLudwig Brieger (1849–1919), derived from toxic.

Toxins can be small molecules, peptides, or proteins that are capable of causing disease on contact with or absorption by body tissues interacting with biological macromolecules such as enzymes or cellular receptors. They vary greatly in their toxicity, ranging from usually minor (such as a beesting) to potentially fatal even at extremely low doses (such as botulinum toxin).