Isolation and Characterization of Ricin E from Castor Beans

Abstract

A toxic protein, distinct from ricin D, was isolated from castor beans produced in Japan and referred to as ricin E. Ricin E was extracted from defatted meal of castor beans and purified by gel filtration through Sephadex G-75 column followed by DEAE- and CM-cellulose column chromatographies. Ricin E was found to be a glycoprotein and had two N-terminal amino acids, Ile and Ala, which were identical to those of ricin D. The molecular weight of ricin E was 64,000 by SDS-polyacrylamide gel electrophoresis and its sedimentation coefficient was 4.45 S. The isoelectric point of ricin E, estimated to be 8.8 by ampholine electrophoresis, was higher than that of ricin D. Ricin E had equal toxicity for mice and equal cytoagglutinating activity for Sarcoma 180 ascites tumor cells to those of ricin D, and this cytoagglutination was inhibited by galactose.