Isolation and Properties of Abrin: a Toxic Protein Inhibiting Protein Synthesis

Abstract

A new procedure is reported for the purification of the toxic protein abrin and for the isolation of its two constituent peptide chains. Abrin was extracted from Semen jequiriti and purified by chromatography on a DEAE‐cellulose column and on a Sepharose‐4B column. The purified toxin behaved as a single protein on polyacrylamide‐gel electrophoresis. The LD 50 dose in mice was about 70 ng indicating that the preparation was about 6‐times as toxic as the most active abrin previously described. After reduction of the toxin with 2‐mercaptoethanol in the presence of galactose the two constituent peptide chains of abrin were isolated by chromatography on a DEAE‐cellulose column.The smaller peptide, denoted the A‐chain, inhibited strongly protein synthesis in a cell‐free system from rabbit reticulocytes, whereas the larger peptide, the B‐chain, lacked this ability.Human erythrocytes pretreated with intact abrin or with B‐chain were agglutinated by an antiserum against abrin, whereas erythrocytes pretreated with A‐chain were not agglutinated under these conditions.The results indicate that the toxic action of abrin is associated with the A‐chain and that the B‐chain functions as a “carrier” moiety necessary for binding of the toxin to the cell surface.