Studies on Proteolysis in Stored Muscle

Part II. Purification and Properties of a Proteolytic Enzyme, Cathepsin D, from Rabbit Muscle

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Presence of high cathepsin D activity in the aqueous extract of the acetone-dried powder from rabbit muscle (L. dorsi) was observed. By fractionation with acetone and by DEAE-Sephadex chromatography, electrophoretically homogenous enzyme with the specific activity of 12, 620 was isolated, and this value was 3600 times of the original sarcoplasmic cathepsin D activity.
Its activity to hydrolyze denatured hemoglobin was maximal at pH 4.0 and at 40_??_47°C. Slight inhibition by zinc and manganese ions (0.01M) was observed. No enhance-ment of the activity by any metal ions and sulfhydryl compounds examined was observed.
This enzyme was stable at fairly acidic pH, and the loss of its activity, incubated for 10 min at pH 3.0, was about 50% and 90%, at 60°C and 70°C, respectively.
The purified cathepsin D in this report showed similar properties as sarcoplasmic cathepsin, and cathepsin D from spleen. However, the present purified cathepsin D was different from the latter cathepsin in the stability at acidic pH.