Two Phytotoxic Anti-Tumor Proteins: Ricin and Abrin

Two phytotoxic proteins, ricin and abrin, have been isolated and purified, and single crystals suitable for x-ray diffraction study have been obtained. Ricin crystals belong to space group C2 with a = 177.3 A, b = 57.3 A, c = 92.2 A, and β = 105°40′. The asymmetric unit contains 1 molecule of molecular weight 50,000, as estimated from crystallographic data and measurements of the crystal water content (68% by weight) and density (1.142 g per cm3). Abrin crystals possess a probable space group P212121 with a = 74.9 A, b = 269.8 A, and c = 70.3 A, with 2 molecules of molecular weight 65,000 in the asymmetric unit.