[Catalytic properties of cathepsin D from the brains of normal and irradiated animals].

Biospecific sorbent, hemoglobin-biogel P-300, was used for purification of cathepsin D from the brain and spleen of a cat and from the brain of normal and irradiated rats. 800 R irradiation of rats in 7 days causes changes in the catalytic properties of cathepsin D: shift of the pH-optimum of the activity, increase in the enzyme affinity to the substrate (hemoglobin) and inhibitor (pepstatin), changes in the activation energy. These changes may be due to the destruction of the processes of posttranscriptional modification of the enzymes at the late stage of the radiation pathology. The temperature dependence of the enzyme reaction catalyzed by cathepsin D from different tissues expressed in the Arrhenius coordinates is characterized by changes in the activation energy in the high-temperature region beginning with the critical temperature (26-30 degrees C). The results obtained may be explained by the presence of cathepsin E admixtures in the purified cathepsin D preparation (in spleen) or by the presence of cathepsin D isoforms catalyzing hemoglobin hydrolysis with different activation energy.