Purification and Properties of Carp Muscle Cathepsin D

A carp muscle cathepsin was purified as an electrophoretically homogeneous preparation. The preparation represented about 2,000‐fold purification and about 4% yield against the crude extract. The activity against hemoglobin was maximal at pH 2.6—2.8 with 0.6M buffer and near 3.2 with 0.12M buffer and at 50°C. The molecular weight was found to be 41,000 and the isoelectric point to be pH 5.4. From the effect of various inhibitors on the enzyme activity, the enzyme was identified as cathepsin D under the classification of Barret. Carp muscle cathepsin D hydrolyzed myofibrils optimally at pH 3–4, but did not above pH 6.0. The participation of the enzyme in autolysis is very doubtful.