Ricin (None)

Ricin is a highly potent toxin and lectin produced in the seeds of the castor oil plant, *Ricinus communis*. It is a glycosylated heterodimeric protein consisting of an A chain (RTA), which inhibits ribosomes, and a B chain (RTB), which facilitates cellular entry. Exposure can lead to severe symptoms including pulmonary edema, gastrointestinal distress, and multi-organ failure. There is no antidote, and treatment is supportive.

Ricin A chain (RTA) functions as an N-glycoside hydrolase that irreversibly inactivates ribosomes by removing an adenine residue from rRNA, halting protein synthesis. Ricin B chain (RTB) binds terminal galactose residues on cell surfaces, facilitating entry of the A chain into cells via endocytosis.