Inactivation studies of the leucocyte inhibitor of urokinase by cathepsin D

Abstract

Leucocytes contain an urokinase inhibitor, that can be inactivated by cathepsin D. In this work biochemical and immunological studies on the inactivation of this inhibitor by cathepsin D are presented. Examinations by polyacrylamide gel electrophoresis and SDS electrophoresis indicate that cathepsin D inactivates urokinase inhibitor by hydrolysis of the inhibitor molecule and that the degradation needed for total inactivation is different from that for formation of the precipitin line with antibodies. The conversion of active inhibitor into inactive protein proceeds catalytically.

An endogenous inhibitor of cysteine and serine proteinases from spleen

“…It was already known that these protein isoinhibitors inhibit intracellular proteinases of cysteine and serine type. We had also found that cathepsin D does not inactivate (degrade) sericystatin, whereas it does inactivate other types of intracellular inhibitors, such as the inhibitors of urokinase [17,18] and elastase [17].…”