Ricin inhibition of in vitro protein synthesis by plant ribosomes

Abstract

In vitro translation systems were prepared with supernatant factors from wheat germ and 80S ribosomes from wheat germ, barley [Hordeum vulgare] embryos, watermelon [Citrullus vulgaris, Schrad.] cotyledons, pea [Pisum sativum L.] cotyledons and castor bean [Ricinus communis L.] endosperm. Ricin A-chain, which strongly inhibits protein synthesis by mammalian ribosomes, inhibited all of the plant ribosomal systems by 50% when present at 25-45 .mu.g/ml-.apprxeq. 23,000 times the concentration needed to inhibit mammalian systems. R. communis agglutinin A-chain, a protein similar to ricin A-chain, inhibited translation by the plant systems 50% at concentrations 5-10 times those of the ricin A-chain. Ribosomes from castor bean endosperm, the source of ricin and the agglutinin, were just as susceptible to the inhibitors as were ribosomes from the other 4 plants. Compartmentation of the inhibitors within vacuoles derived from protein bodies of the endosperm appears to be responsible for protecting cytoplasmic protein synthesis during germination of castor beans.