[User-contributed article for Biology-Online.org]
"Ricin is protein toxin found in castor beans which are obtained from the plant _Ricinus communis_ and it is a residual product obtained during the production of castor oil has applications as a purgative, an engine lubricant, and as a component of brake and hydraulic fluid. Ricin can be in the form of a powder, a mist, or a pellet.
Manufacture of Ricin
One million tons of castor beans are used every year for producing the oil. The waste mash obtain from the oil production process can have as much as 5 percent ricin by weight and it is easily and inexpensively isolated via a simple process in a low technology setting using materials easily obtainable.
Structure And Biochemistry Of Ricin
The tertiary structure of ricin was shown to be a globular, glycosylated heterodimer of approximately 60-65 kDA. Ricin toxin A chain (RTA) and ricin toxin B chain (RTB) are of similar molecular weight, approximately 32 kDA and 34 kDA respectively.
*Ricin A Chain is an N-glycoside hydrolase composed of 267 amino acids. It has three structural domains with approximately 50% of the polypeptide arranged into alpha-helices and beta-sheets. The three domains form a pronounced cleft that is the active site of RTA.
*Ricin B Chain is a lectin composed of 262 amino acids that is able to bind terminal galactose residues on cell surfaces. RTB form a bilobal, structure lacking alpha-helices or beta-sheets where individual lobes contain three subdomains. At least one of these three subdomains in each homologous lobe possesses a sugar-binding pocket that gives RTB its functional character.