Now Polonium...... then Ricin!!!!

Alexander Litvinenko was assasinated in london recently. He was poisoned by radioactive Polonium 210.

Alexander Litvinenko had earlier accused the Kremblin of involvement in the death of about 300 people in Russia in 1999.

This is not the first time Russia stands accused of silencing its critics abroad through assassination.

In 1978, Georgi Markov, a communist defector was killed by a tiny pellet of a substance called Ricin.

He was Bulgarian. He took refuge in London and worked as a broadcaster in BBC. He criticized the Bulgarian communist regime. It is believed by many that this lead Bulgarian government to seek KGB's assistance in silencing him.

On September 7, 1978 he developed high fever and was admitted to the hospital. He died in three days. The cause of death was not clear. Before his death, he recalled an incident, which was key to unraveling this successful assassination attempt.

He was waiting at the bus stop near the Water Loo bridge when he felt a stinging pain in his legs. He turned and saw a man pick up his umbrella and apologize. He (probably) ignored it. But, by the time he realized that it was no accident, it was too late.

He died on September 11, 1978. During his postmortem investigation, forensic pathologists discovered a spherical pellet the size of a tiny pin-head. The pellet had two holes the size of 0.35mm drilled into it. Traces of Ricin was was found in those holes.

Ricin is a toxin. According to FBI, it is one of three most dangerous substances on Earth. It is perhaps the most easily available bioweapon.

Ricin is a protein found in the castor plant (Ricinus communis), the one from which we get Castor oil. This grows in almost all tropical countries. The toxic effects of castor seeds are well known.

Ricin is a very powerful cytotoxin. It belongs to a group of toxins called Ribosome Inactivation Proteins. Ricin is a Type 2 RIP. That is it has 2 poypeptide chains - one to bind to the cell membrane and the other to enter the cell and inactivate the ribosome.

The RTA chain of this heterodimeric protein gains entry into the cell with the help of RTB chain. Once inside, the RTA (a 267 residue long polypeptide) exhibits its N - glycosidase activity by removing A4324 in the 28S rRNA of 60 S subunit of the ribosome. Removal of this prevents the binding of elongation factors. This halts protein synthesis. The cell ultimately dies.

The toxic effects of this protein may develop as soon as within 2 hours of exposure. The symptoms of the ricin poisoning varies with the system that is exposed. It is quite difficult to zero in on the toxin very easily.

There is no vaccine for the protein. There is no direct cure. It is easily available and it is not that difficult to spot Castor plant in any country!!!

All these make it the most efficient bioweapon candidate. And, the 'umbrella murder' Georgi Markov brought the tropical toxin to the lime-light.