Abstract
Cathepsin D (EC. 3.4.4.23) from the skeletal muscle of fresh water fish Tilapia mossambica was purified 114-fold with 14% recovery by employing conventional gel chromatography procedures. The purified enzyme appeared to be homogeneous by Polyacrylamide gel electrophoresis. The apparent molecular weight of the enzyme was found to be 38,000 by Sephadex G–100 column chromatography. The enzyme exhibited dual pH optima at pH 2.8 and 3.8 when denatured hemoglobin was used as the substrate. However, the degradation of endogenous sarcoplasmic proteins occurred maximally at pH 5.0. The optimum temperature of enzyme assay was 50°C. The enzyme displayed heat stability at 60°C in presence of substrate, while in the absence of substrate it lost 95% of activity during incubation for 60 min at 60°C. Sulphydryl compounds and divalent metal ions had no effect on the enzyme activity. However NaCl at 10% concentration inactivated the enzyme almost completely.
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