Effect of Antiviral Agents on Ricin Toxicity: Protection by Zidovudine

摘要

Ricin is a toxic protein obtained from the seeds of Ricinus communis. The ricinmolecule (MW 60,000) is composed of two protein chains, A and B, which are linked by a disulphide bond 1. The B-chain binds to a galactose residue on the cell surface, thus facilitating transport of the A-chain into the cytoplasm (1). Ricin exhibits N-glycosidase activity, which removes an adenine base from the 28S rRNA, resulting in inhibition of protein elongation (2). Ricin A-chain has a homology at the domain level to RNase H from Escherichia coli and two regions of the pol gene product of retroviral reverse transcriptases (3). Several residues conserved among the ribosome inhibitors, E. coli RNase H, and retroviral integrase proteins, occupy a prominent cleft in the ribosome inhibitor ricin, suggesting a role in binding or catalysis 3. Ricin has an antitumour effect on Ehrlich ascites tumour cells in mice (4), and it has been tested for its effects on different human tumours 5. We have investigated the possibility that antiviral agents may reduce the effects of ricin.