Ricin, one of the deadliest protein toxins, shares its origins with the ubiquitous castor oil — both are derived from the castor bean plant (Ricinus communis L.). Castor oil contains high amounts of ricinoleic, linoleic, and oleic fatty acids, and it is commonly used for technological purposes and as a drug and dietary supplement. (Castor oil has a laxative effect because ricinoleic acid irritates the colon receptors and increases peristalsis [1].) Heating during manufacturing inactivates ricin in castor oil, but the poison can be isolated from the castor oilcake.

Ricin is a Type 2 ribosome-inactivating protein (RIP), a globular heterodimeric glycosylated protein with A and B chains [2]. Type 1 RIPs lack the B chain, which mediates the poison’s entrance to the cytoplasm of a human cell via interaction with surface glycoproteins. Once inside, ricin is not hydrolyzed in lysosomes because of its stability across a wide pH range. Instead, its A chain inactivates the cell’s ribosomes through destruction of a specific adenine inside the large ribosomal subunit. One molecule of toxin can irreversibly inactivate 1500 ribosomes per minute [3] The symptoms of ricin poisoning vary depending on the type of exposure. If ingested, ricin can cause severe vomiting and diarrhea requiring immediate medical attention. The pulp of several castor plant seeds may be lethal for the average adult. If ricin is inhaled, symptoms can include fever, cough, nausea, and tightness in the chest. Multiple intelligence services have taken advantage of the lethality of ricin. The most well-known case occurred in Great Britain in 1978, when the famous Bulgarian writer and dissident Georgi Markov was poisoned [4]. Although ricin poses significant dangers, it also has therapeutic potential. For example, it can be fused to specific antibodies and transferred to the malignant cells that produce greater amounts of the surface glycoproteins that interact with ricin. By exploiting its very effective route of cell entry, perhaps ricin will become the basis of a highly-specific cancer therapy [5].

Date: Apr 19, 2012


  1. Gaginella TS, Phillips SF., Am J Dig Dis. 1975 Dec;20(12):1171-7.
  2. Rutenber E, et al., Proteins. 1991;10(3):240-50.
  3. Musshoff F, Madea B., Drug Test Anal. 2009 Apr;1(4):184-91.
  4. Papaloucas M, et al., Pak J Biol Sci. 2008 Oct 1;11(19):2370-1.
  5. Lord MJ, et al., Toxicol Rev. 2003;22(1):53-64.