For characterization of ricin gene see: Nucleic Acids Res 1985 Nov 25;13(22):8019-33
The protein ricin (pronounced [?ra?s?n]) is a toxin from the castor bean (Ricinus communis). Ricin can be extracted from castor beans and is known to have an average lethal dose in humans of 0.2 milligrams (1/5,000th of a gram), though some sources give higher figures . It is considered to be twice as deadly as cobra venom.
Ricin is poisonous if inhaled, injected, or ingested, acting as a toxin by the inhibition of protein synthesis. There is no known antidote; only symptomatic and supportive treatment is available. Long term organ damage is likely in survivors. In small doses, such as the typical dose contained in a measure of castor oil, ricin causes digestive tract cramps. Ingested in larger doses, ricin causes severe diarrhea and victims can die of shock. (See abrin).
Although the castor bean plant has long been noted for its toxicity, ricin was first isolated and named in 1888 by Hermann Stillmark. Modern feed-making techniques break down the ricin in castor beans by heating at 140 degrees Celsius for 20 minutes, although some studies suggest that residual toxic effects may linger. Although one seed contains enough ricin to kill an adult human, they may pass harmlessly through the digestive system if swallowed whole. . Typically 2.5–20 raw seeds can kill an adult human; 4 a rabbit, 5 a sheep, 6 an ox, 6 a horse, 7 a pig, 11 a dog, but 80 for cocks and ducks. As little as one castor bean, about 0.5 grams, may be fatal in a child.
Ricin consists of two distinct protein chains (almost 30kDa each) that are linked to each other by disulfide bond:
* Ricin A is toxic to the cell by interfering with Ribosomes, responsible for protein synthesis * Ricin B is important in assisting ricin A's entry into a cell by binding with a cell surface component.
Many plants such as barley have the A chain but not the B chain. Since people do not get sick from eating large amounts of such products, ricin A is of extremely low toxicity if and only if the B chain is not present.
Ricin is easily purified from castor-oil manufacturing waste. The seed-pulp left over from pressing for castor oil contains on average about 5 per cent of ricin. Since 0.2 mg of purified Ricin constitutes a fatal dose, this is a considerable amount of ricin.