Correlation of inhibition of ribosomal GTPase and protein synthesis by abrin and ricin.

The rate of inhibition of protein synthesis and ribosome-dependent GTPase activity by abrin and ricin was determined. Ribosomes were treated with toxin A-chains for increasing periods of time and they assayed for their ability to synthesize polyphenylalanine and hydrolyze GTP. The rate of inhibition of GTPase activity of the 60S subunit derived 8S ribonucleoprotein complex was also determined. Although the degree of maximal inhibition of protein synthesis and GTPase activity was different, the rates of inhibition were almost identical. The results support a conclusion that abrin and ricin inhibit protein synthesis by inactivating ribosome-dependent GTPase.