Kinetic parameters for the generation of endothelins-1,-2 and -3 by human cathepsin E

The specific conversion of human endothelin (ET) precursors big ET-1, big ET-2 and big ET-3 into their respective ET by cathepsin E was examined. Comparable pH optima were obtained for ET-1 and ET-2 generation, whereas effective conversion of big ET-3 into ET-3 necessitated a lower pH value. Determination of kinetic parameters (Km, kcat.) for all three conversions indicated that the precursors were efficiently bound by cathepsin E. The significance of the values obtained for the catalytic-centre activities and the effect of a specific inhibitor are discussed.