Alpha-sarcin impairs the N-glycosidase activity of ricin on ribosomes.

In a recently described method the RNA N-glycosidase activity of ricin is measured by h.p.l.c. determination of the adenine released from ribosomes after conversion of the base into its fluorescent 1-N6-etheno derivative [Zamboni et al. (1989) Biochem. J., 259, in press]. Unlike previously available methods, based on the separation of RNA fragments by gel electrophoresis, the new method allows one to investigate the activity of ricin on ribosomes pretreated with alpha-sarcin, a cytotoxin which cleaves 28S rRNA at one nucleotide distance from the site of attack of ricin. alpha-Sarcin makes ribosomes a poor substrate for ricin, the release of adenine requiring concentrations of ricin 50-times higher than those effective on untreated ribosomes.