Partial purification and properties of cathepsin D in the retinal pigment epithelium

Cathespin D from the retinal pigment epithelium of bovine eyes was purified about 25-fold from a crude extract of retinal pigment epithelium by acid treatment, ammonium sulfate fractionation, and Sephadex G-200 column chromatography. The purified enzyme hydrolyzed bovine serum albumin optimally at pH values close to 4.0. Exposure of the enzyme to 60 degrees C. for 2 minutes resulted in 50 per cent inactivation of the activity. The enzyme activity was completely inhibited by 0.1 microgram per milliliter of pepstatin, slightly inhibited by trasylol, and not affected by soybean trypsin inhibitor. The apparent molecular weight of cathepsin D was estimated to be about 60,000 by gel filtration on Sephadex G-200.