STUDIES OF THE PROPERTIES OF THE INSULIN PROTEASE OF RAT-LIVER

Difficulties encountered in the purification of the cytosolic insulin-degrading protease of rat liver have led to an investigation of its properties related to this problem. A calcium phosphate gel-purified enzyme preparation was dispersed by ion-exchange chromatography into fractions of lowered specific activity and yield (34%). Recombination of active fractions resulted in a 2.5-fold increase in apparent yield with no increase in purification. Only adsorption to the entire length of an anion-exchange column with stepwise salt elution resulted in significant purification. Dispersion of activity was also seen on Sephadex G-150 but not on Sepharose 6B. In the latter system symmetrical elution of activity together with separation from a recently described globin protease activity was achieved. The protease is probably a complex of rather easily dissociating units, which severely complicates its purification. An earlier study of the enzyme in rat muscle failed to recognize this problem and evidently qualifies the purification reported.