DISTRIBUTION AND PROPERTIES OF MAJOR RIBOSOME-INACTIVATING PROTEINS (28-S RIBOSOMAL-RNA N-GLYCOSIDASES) OF THE PLANT SAPONARIA-OFFICINALIS L (CARYOPHYLLACEAE)

We have studied the distribution of the protein synthesis inhibitory a ctivity in the tissues of Saponaria officinalis L. (Caryophyllaceae). Seven major saporins, ribosome-inactivating proteins, were purified to apparent homogeneity from leaves, roots and seeds using a new procedu re of RIPs isolation including ion-exchange and hydrophobic chromatogr aphy. They all catalysed the depurination of rat liver ribosomes, whic h generate the Endo's diagnostic rRNA fragment upon treatment with aci d aniline, thus indicating that A4324 from the 28S rRNA has been relea sed (Endo et al. (1987) J. Biol. Chem. 262, 5908-5912). The molecular mass of saporins by SDS-PAGE ranged between 30.2 and 31.6 kDa and by g el-filtration between 27.5 and 30.1 kDa. Amino acid composition and am ino-terminal amino acid sequence indicate that all saporins may be con sidered isoforms. Only two saporins present in roots were glycosylated (SO-R1 and SO-R3). All saporins are very active on cell-free translat ion systems derived from rabbit reticulocyte lysates, rat liver, Triti cum aestivum L., Cucumis sativus L. and Vicia sativa L. However, they are poor inhibitors of an Escherichia coli translation system. They in hibit protein synthesis in HeLa, BeWo and NB 100 cells, HeLa cells bei ng the most resistant. The enzymatic activity of at least one saporin isoform was dependent on magnesium concentration in the standard rat l iver cell-free system.