Specificity and Biological Role of Cathepsin D

Abstract

Cathepsin D was originally isolated from bovine spleen by Press, Porter and Cebra in 1960 (1). My interest in this enzyme was aroused by the observation of its high levels of activity in the involuting post-partum uterus (2); in fact, the uterus contains high levels of this enzyme even in the normal nongravid condition. This led to the purification of cathepsin D from the bovine uterus (3). Uterine cathepsin D was insensitive to a large number of inhibitors specific for thiol, serine, and metallo-proteases, and incapable of cleaving a large group of synthetic peptide substrates typically used for the known proteases (4). Strong inhibition could be obtained only by the use of heavy metals such as Pb²⁺ and Hg²⁺. The specificity was determined by the use of the S-sulfo B chain of insulin. Most rapid splitting was at the bonds Leu₁₅-Tyr₁₆, Phe₂₄-Phe₂₅ and Phe₂₅-Tyr26; secondary splitting was found at G1u₁₃-Ala₁₄, and Tyr₁₆-Leu₁₇. These points of cleavage are the same as reported by Press et al. (1). Minor splits were also observed at Phe_l-Va1₂ and Ala₁₄-Leu₁₅ (4).