Partial Purification of Salmon Muscle Cathepsins

SUMMARY Salmon muscle cathepsins hydrolyzed denatured hemoglobin optimally at pH 3.7 with two minor pH optima noted at pH 7.0 and 8.5. Cathepsins optimally active at pH 3.7 and extracted with 0.2 N KCI, were partially purified by (1) precipitation of inactive protein at pH 5.5, (2) (NH 4 ) 2 SO 4 fractionation, and (3) column chromatography on DEAE‐cellulose. Two cathepsins appeared to be separated by this procedure; one was purified 27‐fold with 17% recovery and the other was purified 116‐fold with 6.8% recovery.