SUMMARY— A cathepsin has been purified from chicken leg muscle by ammonium sulfate fractionation and by chromatography on carboxy methyl‐ and diethylaminoethylcellulose. With respect to the specific activity of the initial 2% potassium chloride extract the cathepsin was purified 580. fold. The purified cathepsin hydrolyzed urea‐denatured hemoglobin readily at pH 4.40, but it had no activity on a‐N‐benzyloxy‐carbonyl‐L‐glutamyl‐L‐tyrosine, a‐N‐benzoyl‐L‐argininamide and a‐N‐acetyl‐L‐tyrosinamide.
The data indicate the preparation was cathepsin D and that it did not contain cathepsins A, B, and C. The cathepsin preparation had no activity on actomyosin at pH 4.95 and 5.90 as measured by viscosity and gel‐filtration methods. On the other hand trypsin, with 0.014 the potential activity of the cathepsin used and at pH 7.9, hydrolyzed actomyosin readily. While the cathepsin prepared here, probably cathepsin D, did not hydrolyze actomyosin, the data do not exclude the possibility of hydrolysis of actomyosin by other cathepsins or by cathepsin D in combination with other cathepsins.