Toxic News

Now You Know How Bacteria Feel

When you take an antibiotic, you expect it to kill your infection without hurting you. Lots of antibiotics take advantage of differences between your “eukaryotic” cells (cells with nuclei) and bacteria’s “prokaryotic” cells (no nuclei). A typical antibiotic will shut down protein synthesis in bacteria’s ribosomes, which are the fantastically complicated little factories in cells (about the size of a small virus) where proteins are built according to instructions delivered by RNA. Stop protein synthesis and the cell dies. Luckily for you, your ribosomes use a different construction process from bacteria’s, so the antibiotic doesn’t shut down your protein synthesis and kill your cells.

Castor Beans

Unless you ingest ricin, that is. Ricin is a protein found in the seeds of the castor bean plant (Ricinus communis). It messes up the protein synthesis in the ribosomes of eukaryotic cells, that is, nucleated cells, like yours and mine. In other words, ricin did to Bulgarian dissident Georgi Markov in 1978 pretty much what tetracycline does to Rocky Mountain Spotted Fever. There is a difference, though. Unlike the natural toxins in common antibiotics, which lock on one-to-one with their target molecules to disrupt bacteria’s protein synthesis, ricin jumps from ribosome to ribosome, shutting down one after another. As a result, a single molecule of ricin can kill a whole cell. This makes ricin one of the most toxic natural substances known, a thousand times as toxic as cyanide. A mere 75 micrograms can be a deadly dose in an adult human; one castor bean contains something like 1,000 micrograms.

Biochemists report recent progress in developing a ricin antidote and a ricin vaccine, but don’t count on them yet. Likewise, we may figure out someday how to target cancer cells with ricin, but for now it’s just bad news for all of your cells.

There are worse toxins than ricin, but few so widely available. Castor bean seeds are used in the production not only of the laxative castor oil, but also brake fluid, varnish, soap, and ink. Ricin is soluble in water but not in oil, so castor oil is OK from the point of view of health, if not of taste. But stay away from the bean pulp left over after castor oil production, and don’t eat unprocessed castor beans, unless you’re trying to cure Gaia of her human disease.

More cheerful news about poisonings throughout history here.