The chemistry in Breaking Bad
Ricin and glycoside poisons
Walter uses these two poisons in the show. Ricin is a globular glycoprotein meaning it has a round structure and has oligosaccharide chains (carbohydrate chains) linked to the main polypeptide chain. Ricin contains two chains as seen left, Chain A (red) is the toxic chain and is composed of 267 10 amino acids and is present in many non-toxic such as barley because without chain B chain A cannot enter the cell. Chain B is a lectin (carbohydrate binding protein) composed of 262 10 amino acids. The chains are linked by a single disulfide bond which is very strong due to end-to-end overlap of sulphurs unpaired 3p orbitals. Ricin is relatively slow acting: ricin takes about 36-72 11 hours till fatality if inhaled or injected and about 3-5 11 days if ingested. Some symptoms from ingestion include vomiting and
Figure showing the protein structure of ricin. Chain A in red, Chain B in blue from Molecule of the month: Ricin
diarrhoea as well as seizures. Ricin is a ribosome-inactivating toxin. Chain B acts as the transport mechanism for the toxic chain A by attaching onto glycoproteins which make up outer surface receptor proteins on the cell membrane. After attachment to the glycoprotein receptor, the ricin toxin enters the cell through endocytosis where the protein is engulfed by the cell
Figure showing the mechanism of action for the ricin toxin (Gal et al. 2017)
membrane bringing it to the cell. Most of the engulfed ricin toxin is degraded in lysosomes by enzymes then recycled back to the cell surface. The remaining ricin toxin is transported to the endoplasmic reticulum which produces proteins and acts as a transport system to and from the nucleus. In the endoplasmic reticulum chain A is separated from chain B by the enzyme protein disulfide isomerase which breaks the disulfide bond. The chain A then attaches to the ribosomal RNA inhibiting protein elongation, and therefore formation. One molecule of ricin chain A can inhibit 1500-2000 enzymes per minute. 11 Walter also uses the ‘Lily of the valley’ plant as a poison to have similar symptoms as ricin but be less lethal. The berry from the plant contains cardioactive glycosides. 38 different cardiac glycosides are present in the plant with the general formula shown below. 12 The mechanism of action of cardiac glycosides is to inhibit the Na + K + ATPase enzyme (sodium-potassium pump). This causes sodium to build up in the cells, thereby decreasing the ability of the sodium-calcium pump to push calcium out of cells. This slows down your heart rate but increases the force of contractions. Therefore, cardiac glycosides are also often used as medicines for high heart rate or heart failure. However, the toxicity comes in high doses, as there is a high amount of intracellular Ca 2+ and Na + ions. This can lead to partial membrane depolarization, where the membrane becomes more positively charged in certain
10 Wright and Robertus 1987. 11 Moshiri et al. 2016. 12 Lily of the Valley (convallaria majalis).
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