How does potassium cyanide cause sudden death?

How does potassium cyanide cause sudden death?


A small but deadly cluster of potassium cyanide crystals near a one eurocent coin on 27 May 2005.

A small but deadly cluster of potassium cyanide crystals near a one eurocent coin, May 27, 2005. | Photo credit: Morienus (CC BY-SA 3.0)

A: When potassium cyanide is consumed, it causes death by slowly blocking the supply of oxygen to the cells in our body by forming complexes with hemoglobin and cytochrome (a protein that helps cells respire), thereby eliminating their ability to transport or exchange oxygen.

Normally, oxygen is carried from the lungs to parts of the body through the blood via hemoglobin — the iron-containing, oxygen-carrying molecule of red blood cells.

Hemoglobin is composed of a globular protein and four heme groups. The iron (in the ferrous state) present in these heme complexes can bind to either an oxygen molecule or a water molecule or exchange one for the other without any difficulty. It is because of this ability that hemoglobin is able to pick up oxygen from the lungs, carry it to the cells and bring back water in return.

Cells breathe in oxygen with the help of myoglobin (a hemoglobin-like protein in cells) and cytochromes, which carry electrons. Certain forms of cytochromes and hemoglobin are also responsible for causing sudden death from cyanide poisoning.

When potassium cyanide is consumed, it splits into a potassium ion and a cyanide ion. The cyanide ion has a greater affinity than the ferrous ion. As a result it occupies the space reserved for oxygen in hemoglobin. This process is irreversible and prevents the transfer of oxygen.

One form of cytochrome, called cytochrome-a, binds with the cyanide ion, immobilizing iron to such an extent that it does not participate in electron transfer in the cell. This prevents oxygen uptake by the cell.

Symptoms of cyanide poisoning are dizziness, headache and bluish skin. If not treated immediately, unconsciousness and death may occur.

A. Karthikeyan, Udumalpet; C. Ravi Chandra, Secunderabad; and R. Rama, Chennai


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