Enhancement of cathepsin B activity in irradiated mouse testes.

The irradiation of mouse testes at 600 rads is accompanied by extensive tissue destruction which ultimately results in a 70% loss of organ weight but displays appreciable recovery which is usually complete by week 18. The attrition phase of testicular weight is concurrent with a conspicuous elevation in cathepsin B activity. This is interpreted to reflect the extensive proteolysis that must form the basis for such tissue weight loss. The recovery period, in contrast, is characterized by an attenuation in the activity of the enzyme. Further analyses reveal that the rise in hydrolytic activity is not due to lysosomal membrane breakage. Nor does it seem to be related to an increase in the number of lysosomes. Instead, our data are more consistent with the contention that the rise in cathepsin B activity may be associated with an increase in protein synthesis. As a result, some lysosomes may contain a larger number of enzyme molecules. This hypothesis is supported by our demonstration that radiation induces a distinct shift in the density of lysosomes toward the heavier components. The significance of such radiation-induced enhancement of protein synthesis in terms of a general response of tissues to radiation damage is discussed.