The purification and properties of a proteolytic enzyme, rabbit cathepsin E, and further studies on rabbit cathepsin D

Abstract

Two proteolytic enzymes were found in relatively large amounts in aqueous extracts of rabbit bone marrow. One of these enzymes was shown to be the same as the enzyme obtained from rabbit spleen by Lapresle and Webb (1960), and has been named rabbit cathepsin D. A further step in the purification of cathepsin D is described. Its electrophoretic mobility in agar gel at pH 8.2 was -17 x 10-5 cm. 2v-1 sec.-1. The other proteolytic enzyme has been named rabbit cathepsin E. It has been purified by chromatography on diethylaminoethylcellulose and gel-filtration with Sephadex G-75. It is present in only small amounts in rabbit spleen. With human serum albumin as substrate, cathepsin E has an optimum pH at 2.5, and is not affected by cysteine, iodoacetate or di-isopropyl phosphorofluoridate. It is heat-labile. Cathepsin E does not hydrolyse the synthetic substrates for cathepsins A, B and C. The electrophoretic mobility of cathepsin E in agar gel at pH 8.2 is -7.2 X 10-5 cm2. v-1 sec.-1.