Changes in rat liver immunoreactive cathepsin D after cycloheximide

A rocket immunoelectrophoretic procedure has been developed for the assay of cathepsin D (EC 3.4.23.5) immunoreactive protein, in a 10-100 ng range, directly on crude soluble liver homogenate extracts. By this method, the drop in activity of rat liver cathepsin D effected by repeated doses of cycloheximide, a protein synthesis inhibitor, reflects a parallel change in total enzyme protein content, the specific activity being stable in the course of the treatment. These observations are compatible with the hypothesis that ongoing enzyme degradation, coupled with impaired synthesis, accounts for such a decline of cathepsin D.