Detection of Ricin in Clinical and Food Samples

摘要

The toxic protein ricin is produced by the plant Ricinus communis, commonly known as the castor bean. Ricin is a 64 kDa protein composed of two chains, each approximately 32 kDa in size. The two chains are disulfide linked. The B-chain binds to cells and promotes internalization of the toxin, delivering the catalytically-active A-chain to its target. The A-chain is an RNA N-glycosidase which inactivates ribosomes responsible for protein synthesis. This ribosomal inactivation occurs through depurination of the 28S ribosomal RNA (rRNA) by the A-chain, which prohibits complex formation with a protein known as elongation factor 2 (EF-2). It is the inability of the depurinated 28S rRNA to complex with EF-2 which inhibits protein synthesis and causes cell death. One ricin molecule can depurinate all ribosomes within a single cell, and it is the action of ricin upon many ribosomes that is the reason for a low LD50 with binding and internalization into the cell as the toxicity-determining step.