Purification of acid proteinases from calf brain

The purification was begun with acetone precipitation of minced brain tissue with subsequent proteinase extraction with 0.2 M sodium formate buffer (pH 3.5), reprecipitation with acetone and dialysis. Chromatographic separation on Sephadex G-200, DEAE-Sephadex A-50 and CM-cellulose was carried out in that order. Upon ion-exchange chromatography multiple forms of acid proteinases emerged; two of them were obviously identical with cathepsin D (EC 3.4.23.5), and two of them exhibited properties of cathepsin B (EC 3.4.22.1).