Specific Radioprotective Effect of the Mitochondrial Matrix

Abstract

THE ability of the cellular contents to protect enzyme molecules from the destructive action of ionizing radiation is now clearly recognized¹; but there is little quantitative information concerning the specific radio protection offered by the natural intracellular milieu. Irradiation of whole animals suggests that this natural environment affords a high degree of protection from the indirect effects of aqueous radicals and perhaps from direct effects as well². The specificity of this protection can be demonstrated by the irradiation and assay of enzymes uniquely associated with organelles within and without their natural cellular environment. For example, diphosphopyridine nucleotide-pyrophosphorylase, an enzyme contained exclusively in the cell nucleus, is many times more resistant to X-rays in isolated nuclei than is an equally active solution free of nuclei³. In the experiments to be reported, glutamic dehydrogenase, an enzyme believed to be confined to the mitochondrial matrix^4,5, has been irradiated without and within the intact mitochondrion.