Purification and characterization of a digestive cathepsin D proteinase isolated from Tribolium castaneum larvae (Herbst).

A digestive proteinase was isolated from larval extracts of Tribolium castaneum. The enzyme was partially purified using gel-filtration and ion-exchange chromatography. It is an acidic proteinase with a maximal activity at pH 3. Considering its inhibition by Pepstatin A, plus its selectivity to hydrolyze hemoglobin but not bovine serum albumin, it was classified as Cathepsin D proteinase. Its relative molecular weight is 22 kDa and it shows a high sensitivity to temperature. Unlike other cathepsin D found in animals, this enzyme is free of carbohydrate, and its activity is not affected by the presence of different anions which are known to affect the activity of plant aspartic proteinases.