The purification of ricin was reinvestigated. Ricin can be purified by CM-cellulose column chromatography at pH 6.5, followed by gel filtration on Sephadex G-75 at pH 8.0 and finally CM-cellulose column chromatography at pH 7.0. The purified ricin preparation is electrophoretically and ultracentrifugally homogeneous and identical with ricin D in sedimentation coefficient and toxicity. The effects of cupric ion on the solubility and the behavior in CM-cellulose column chromatography of ricin were examined. The purified ricin was precipitated with copper acetate at higher concentrations than 10^-5M and the crystallization of ricin was achieved by dialysis against 0.005M phosphate buffer con-taining 10^-6M of copper acetate at pH 6.5.

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