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Summary
Intracellular distribution of catalase activity after x-irradiation was determined in two types of mouse mammary epithelial tumours, H and DBrB, in a spindle-cell tumour (DBAG) and in a plasma-cell tumour (Adj-PC-5). Livers and kidneys were used for comparison. Catalase activities were assayed from three sub-cellular fractions, mitochondrial, microsomal and cell-sap.
A decrease in catalase activity in the mitochondrial fraction with a concomitant increase in the cell-sap fraction was noted after x-irradiation. The extent of the release of catalase activity from the mitochondrial to the cell-sap fraction differed between the various tissues. The greatest release after x-irradiation was noted in the epithelial tumour (H). This occurrence is obscured in the G and DBrB tumours due to the spontaneous release of this enzyme because of homogenization damage to the boundary membrane in which catalase is encased. It is inferred that the shift in catalase activity from the mitochondrial to the cell-sap fraction is due to the effect of x-irradiation on the boundary membrane of the microbody in which the catalase particle is enveloped, releasing this enzyme. The extent of the release of this enzyme seems to be dependent upon the endogenous quality of the membrane surrounding the catalase.