Studies on the Chemical Nature of the Radiation Protection Factor in Mouse Spleen: I. Enzymatic Inactivation by Deoxyribonuclease and Trypsin

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Abstract
Short-term incubation of mouse spleen homogenates and of spleen nuclei with desoxyribonuclease or with trypsin at 25[degree]C results in the loss of the capacity of such preparations to protect lethally X-irradiated mice (725 to 760 r). Under the same experimental conditions, treatment of spleen homogenates or nuclei with ribonuclease does not inactivate the protective factor. The loss of protective activity of desoxyribonuclease treated nuclei is accompanied by liberation of soluble desoxyribonucleic acid (DNA) from a bound form in the nuclei insoluble at an ionic strength of 0.14 [image] NaCl. Suspension of the particulate nuclei fraction in low ionic strength water (approaching that of distilled water) leads to swelling and solubilization of the desoxyribonucleoprotein; under these conditions the protective activity is lost. The present experimental data support and are consistent with the following conclusions: that the spleen radiation protection factor is non-cellular in nature; and that chemically it is a desoxyribonucleoprotein. The data imply that the structural integrity of spleen DNA-protein, as such, is required for protective activity. The possible mode of action of the spleen factor is discussed in the light of the present findings.

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