On the role of the covalent carbohydrate in the action of ricin.

the covalent carbohydrate in the toxic lectin ricin has been modified by periodate treatment, and analysis of the products of this reaction indicates that only mannose residues are oxidized. HeLa cell toxicity, cell-surface binding, inhibition of cell-free protein synthesis, and other properties have been investigated as functions of the number of mannose residues modified. The data indicate an important role for mannose in ricin conformation and in the endocytotic process; however, mannose appears not to be essential for binding the toxin to cells.