In normal respiration, sugars are oxidised ultimately to form carbon dioxide and water, with the stored energy being extracted to sustain life. This process follows a sequence of steps, each mediated by a specific enzyme. Compound 1080 stops this reaction, leading to a fatal build-up of citric acid in the victim's cells. Interestingly, compound 1080 occurs naturally in the leaves of several species of legume. Presumably it evolved in these plants as a means of reducing herbivores from nibbling their leaves.
Many poisons result from natural sources.
Often plant species employed as foods have to be detoxified before eating. These substances are all 'natural' yet they may cause deaths. Another important class of potential poison is hormones. Hormones are chemicals which initiate reactions in tissues some distance from those where they were produced. Under natural circumstances, hormones are produced by glands and trigger a reaction somewhere else in the body when required.