Ricin inhibition of in vivo protein-synthesis in castor beans

Abstract

Ricin is a potent inhibitor of protein-synthesis by 80 S ribosomes. Experiments in vitro have previously shown that ribosomes from castor bean endosperm, the source of ricin, are just as susceptible to inhibition as ribosomes from other plants. Studies in vivo with castor bean endosperm have now shown that exogenously applied ricin enters the cells and inhibits the incorporation of [ 14C] leucine into protein. Ricin did not affect the uptake of [ 14C] leucine. Galactose and lactose prevented the inhibition of protein-synthesis by ricin by interfering with its uptake. This indicated that ricin entered the cells by a mechanism similar to that in animal cells, by interaction of the B-chain with a receptor. The data from experiments in vivo support the conclusion drawn from the data obtained in vitro, that compartmentation of endogenous ricin within protein bodies/vacuoles protects cytoplasmic protein-synthesis in the endosperm during germination.