On the distribution of ribosome-inactivating proteins amongst plants.

The extracts from various parts (mostly seeds) of 56 different plants were examined for inhibition of protein synthesis by a rabbit reticulocyte lysate. Most extracts inhibited protein synthesis with an ID50 (concentration giving 50% inhibition) of 100 micrograms extract protein per ml, or less. The extracts with high activity were partially purified by CM cellulose chromatography. Protein-containing fractions were separated which inhibited protein synthesis and resembled the ribosome-inactivating proteins from plants previously described. Thus, ribosome-inactivating proteins appear to be virtually ubiquitous in plants.