Which is more potent, Abrin or Ricin?

• A. Abrin (magnitudes more)
• B. Ricin
• C. Equally potent
• D. Unknown potency

Answer: (A)

Abrin is more potent. Both toxins are ribosome-inactivating proteins that halt protein synthesis by removing a specific adenine from the 28S ribosomal RNA, but abrin does this more effectively on a per-molecule basis and tends to enter cells more efficiently. The A chain of abrin has high catalytic activity, and its B chain facilitates cell entry in a way that often results in greater cellular uptake. Because of these factors, a smaller amount of abrin produces a given toxic effect compared with ricin, and measurements across various systems show abrin to be tens to hundreds of times more potent. In short, the combination of stronger enzymatic action and more efficient cell delivery makes abrin magnitudes more potent.