On the Mechanism of Radiation Protection by Cysteamine: An Investigation by Means of Electron Spin Resonance

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Abstract
Cysteamine prevents the crosslinking of deoxyribonucleic acid (DNA) when irradiated by gamma-rays in the form of a nucleoprotein. Electron spin resonance measurements of salmon sperm heads indicate that this protection is due to the transfer of an H atom from the[long dash] SH group of the cysteamine to the radicals produced in DNA. In this way the radiation damage in DNA is restored, and radical combination leading to crosslinking is prevented. O2 competes with the-SH groups for the radiation-produced radicals, and cysteamine repair is more effective in its absence. It is suggested that intracellular [long dash]SH compounds are responsible for restitution of radiation damage within cells and that interference with this repair reaction by O2 is one of the factors responsible for the radio-sensitizing action of O2. Data are also presented on the electron spin resonance spectra at 196[degree]C and at room temperature of irradiated nucleoprotein and its constituents DNA and salmine.