LYCOS RETRIEVER 
Ricin
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Ricin (... known as RCA60) is a potent biotoxin which can be extracted from the castor bean and is considered an important potential bioterrorism weapon. Ricin consists of a lectin component (the B-chain) and a toxin component (the A-chain) linked by a disulfide bond. The A-chain is a ribosome-inactivating enzyme with a molecular weight of 32 kDa that cleaves adenine 4324 of the 28S RNA in the 60S ribosomal subunit. The B-chain is a galactose/N-acetylgalactosamine-binding lectin (34 kDa) which binds to cell surfaces and is detached after endocytosis when the A-chain is released to the cytoplasm. Together, the two chains constitute one of the most potent cytotoxins in nature whereas no toxic effects are known for the isolated single chains. Ricin causes extensive cell death and doses down to 1 mg can be lethal.
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Ricin is a stable toxin easily made from the mash that remains after processing Castor beans (Ricinus communis) for oil. Castor Oil was once used as an oral laxative, but is now used mainly as an industrial lubricant and for preparing leather products. Castor beans are grown agriculturally worldwide and the plants grow wildly in arid parts of the United States. Castor beans are slightly larger than pinto beans, darkly colored with light mottling, and have a small light-brown cap at one end. They have been described as looking like blood-engorged ticks. The beans are not normally used as food.
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Ricin is feared to have a high terrorist potential due to its ready availability, relative ease of extraction, and notoriety via the media. Some reports have indicated that ricin may have been used in the Iran-Iraq war during the 1980s and that quantities of ricin were found in Al Qaeda caves in Afghanistan.
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Ricin has had its fair share of the media spotlight in recent years. Press reports said the toxin turned up in an envelope in the mailroom that serves Senator Bill Frist’s office and a postal handling facility in Greenville, SC. It was ... at the center of a plot in London where suspected al-Qaeda members were trying to make it.
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Ricin's significance as a potential biological warfare toxin relates in part to its wide availability. Ricin was apparently used in the assassination of Bulgarian exile Georgi Markov in London in 1978. Markov was attacked with a specially engineered weapon disguised as an umbrella, which implanted a ricin-containing pellet into his body. This technique was used in at least six other assassination attempts in the late 1970's and early 1980's. In 1994 and 1995, four men from a tax-protest group known as the "Minnesota Patriots Council," were convicted of possessing ricin and conspiring to use it (by mixing it with the solvent DMSO) to murder law enforcement officials. In 1995, a Kansas City oncologist, Deborah Green, attempted to murder her husband by contaminating his food with ricin.
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Ricin consists of two hemagglutinins and two toxins, each containing two polypeptide chains (A and B) joined by disulfide bonds. The toxins are very lethal to cells, acting by inhibiting protein synthesis. The assault begins when the B chain binds to cellular receptors and the toxin is taken into the cell. Once inside, the A chain, consisting of endonuclease activity, acts by inhibiting protein synthesis. The basic structure of ricin is similar to botulinum, cholera, diphtheria, and tetanus toxins.
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Ricin