Autolysis studies of cathepsin D.

Incubation of the single polypeptide chain cathepsin D from bovine spleen at pH 3.5, resulted in the fragmentation of the molecule. This was followed by gel electrophoresis in the presence of dodecyl sulphate, gel filtration, circular dichroism and enzyme activity measurements. Main bands of Mr 30,000 and 15,000 appeared first, followed by bands corresponding to smaller fragments. Conformational changes of the cathepsin D molecule were observed in the near ultraviolet circular dichroism spectrum during the autolysis. Measurements of the initial inactivation rate showed apparent first order kinetics which was biphasic at lower concentrations of the enzyme. The inactivation rate of cathepsin D increases with decreasing enzyme concentration. The presented results are interpreted in terms of autolytic degradation of cathepsin D.