Effects of Irradiation on Sub-cellular Components

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Abstract
Suspensions of microsomes prepared from rat liver form lipid peroxide when irradiated in vitro with electron doses within the range 5–100 krads. Peroxide formation is minimal immediately after irradiation but increases markedly if the microsomes are incubated at 4°, 20° or 37°c. Dilute microsomal suspensions form much more peroxide than concentrated suspensions. The rate of peroxidation stimulated by NADPH is further enhanced by irradiation. During peroxide formation, extensive degradation of the microsomal lipid occurs with the release of malonaldehyde, or related di-aldehyde, into the aqueous medium. Vitamin E or glutathione (mM) are good protectors against radiation-induced peroxidations. O-phenanthroline (0·5 mM) completely abolishes peroxidation in untreated microsomes, but after doses greater than 50 krads o-phenanthroline has less effect on the rate of peroxidation. ADP contaminated with low concentrations of inorganic iron stimulates peroxidation in untreated microsomes, but has much less effect on irradiated microsomes. In sub-components of the microsome fraction, the ‘fluffy layer’, composed mainly of membranes of the endoplasmic reticulum, is the main site of peroxidation after irradiation. Peroxidation in microsomal suspensions is likely to be a result of free-radical attack on unsaturated fatty acids, but alterations in the binding of microsomal non-haem iron, increasing its catalytic activity in peroxidation, may also be an important factor.