First lectin discovered

The first ever substance classed as a lectin (a carbohydrate-binding protein) was discovered to occur in castor beans, the seeds from the plant Ricinus communis. This lectin was revealed to be the toxin ricin, which is among the most toxic natural compounds known to humankind. Ricin was first extracted from castor beans by the Estonian scientist Peter Hermann Stillmark in 1888.

We now know that lectins occur in a wide range of animals (including certain insects, fish, reptiles and mammals, even including humans) and plants; in the latter, they are particularly common in legumes, such as beans, peas and peanuts. They help the plants survive by being able to resist attacks from certain bugs and pathogens. At natural levels, and particularly when cooked, the effect of lectins in such common food crops are harmless to humans; they tend to only become dangerous when these proteins are artificially concentrated. Though certain plant lectins, like ricin in castor beans and abrin contained in the rosary pea (Abrus precatorius), require only a nominal amount to be potentially fatal.

Ricin poisoning can occur in different ways including when it is injected, inhaled or ingested, or when it is absorbed through abraded skin. Symptoms of ricin poisoning may include severe gastrointestinal irritation, vomiting, breathing difficulties, bleeding, the breakdown of red blood cells and the failure of multiple organs in the body, such as the liver and kidneys, which can be fatal.

Ricin poisoning has been identified as the cause of death in numerous murder cases. Probably the most infamous was the assassination of Bulgarian dissident Georgi Ivanov Markov, who was shot with a tiny pellet, later concluded to contain ricin, from the tip of an umbrella on Waterloo Bridge in London, UK, in 1978. Although he was able to describe the suspicious circumstances of the attack, within days, Markov died in hospital on 11 September 1978.