Studies on components of immunotoxins: purification of ricin and its subunits and influence of unreacted antibodies

Abstract

Two ricins were purified from the seeds of Ricinus communis by a simple method based on affinity chromatography allowing large-scale preparations. Separation of these 2 ricins was achieved by ion-exchange chromatography and studies of purified subunits demonstrated that the 2 forms of ricin differed only in their B-chains which showed widely differing isoelectric points. The A-chains isolated from both ricins showed similar biological properties and contained 2 variants, A1 and A2, differing in their molecular weights and carbohydrate contents. These variants could be separated by affinity chromatography on Con-A-Sepharose which bound the A2 variant more tightly than A1. This property allowed us to obtain immunotoxin preparations devoid of free antibodies and to study the in vitro influence of free antibody on immunotoxin activity.