Biochemical studies on ricin. XIX. Isolation and characterization of two constituent polypeptide chains of ricin E.

Abstract

Two constituent polypeptide chains (lle and Ala chains) of ricin E were separated by an affinity chromatography on acid-treated Sepharose 4B in the presence of β-mercaptoethanol, and the Ala chain was purified by CM-cellulose column chromatography at pH 7.0 and crystal-lized. From the analyses of isoelectric points, amino acid compositions and tryptic peptides, it was revealed that the Ile chain will be common in ricin E and ricin D while the Ala chain of ricin E is homologous protein having several amino acid replacements to that of ricin D. Furthermore, the toxicity of the hybrid molecule consisting of the Ile chain of ricin E and the Ala chain of ricin D to malignant cultured cells was determined to be similar to that of ricin D. It was concluded that the difference in the toxicity toward the cultured cells between ricin E and ricin D was due to the difference in the function of Ala chain.