Proteolytic processing of porcine big endothelin-1 catalyzed by cathepsin D

Cathepsin D, a candidate for endothelin-converting enzyme (ECE), was allowed to act on porcine big endothelin-1 (big ET-1, 1-39). The proteinase primarily cleaved the Asp18-Ile19 and Trp21-Val22 bonds of big ET-1(1-39), with a optimum pH of 3.5. The mature ET-1(1-21), generated by the cleavage between Trp21 and Val22, was subsequently degraded by removal of most of the C-terminal tripeptide (Ile19-Ile20-Trp21). Therefore, cathepsin D is by no means a specific ECE, although the proteinase does cleave the Trp21-Val22 bond of big ET-1(1-39) to produce mature ET-1(1-21). The possibility that cathepsin D can act as an endothelin-degrading enzyme in vivo warrants consideration.