Influence of cysteamine on the protection and repair of radiation-induced damage to DNA

Studies of the influence of cysteamine on damage to DNA by ionising radiation, using two methods of examination: EPR and gel-electrophoresis under air and oxygen-free conditions, and at cryogenic and ambient temperatures, enabled us to draw some conclusions as to the most probable reaction pathways in the complicated system of DNA/thiol/oxygen. The DNA-peroxyl radicals formed in the presence of oxygen seem to be effectively deactivated by cysteamine as they were not detected by EPR at higher thiol concentration. The peroxyl radicals, if formed, increase double strand breaks of DNA. The competitive reactions of oxygen/DNA and oxygen/thiol, and their non-linear dependence on the thiol concentration, observed previously, are confirmed by the results of electrophoresis.