Some organisms, such as the castor bean plant (
Ricinus communis), produce substances that inhibit the synthesis of proteins (called translation) within a cell. (The plant, which is native to Africa, is not related to the species of bean plants with which you are likely more familiar.) A protein called ricin, produced within the castor seeds is an extremely potent inhibitor of protein synthesis. In fact, it is one of the strongest natural toxins produced. A single chewed seed can kill child! If the ricin were purified, it would take an amount equivalent to only a few grains of salt to kill an adult. Ricin kills cells by enzymatically cleaving covalent bonds within the large and small ribosomal subunits, rendering the protein-building factories nonfunctional.
