Effect of ribosome treatment on sensitivity to ricin A chain

Rat liver ribosomes treated with catalytic amounts (30 ng/ml) of ricin A chain are inhibited about 80% when assayed immediately. However, the same ribosomes assayed after separation from A chain by centrifugation have partially recovered their activity in the translation of polyuridylic acid. The extent of recovery is dependent on magnesium ion concentration. Even though the activity of A chain-treated ribosomes is increased after centrifugation, they are not sensitive to further treatment with ricin A chain. Except for impure ribosomes, isolated by centrifugation of crude homogenate, the overall sensitivity of ribosomes after different treatments was the same.