| Popis: |
When considering modification of radiobiological damage by any physical or chemical agent, it is necessary to keep in view the role of molecular oxygen present during irradiation of cells and organisms. It has been known for a long time that the yield of mutations and chromosomal aberrations and other effects such as cell killing, can be considerably enhanced by irradiating under oxic conditions, a phenomenon called the “oxygen effect” in radiobiology (Crabtree and Cramer, 1933; Mottram, 1936; Read, 1952; Gray et al., 1953). Several different approaches revealed that the oxygen effect was attributable not to the direct ionization of the chromosome material but to highly reactive intermediates (free radicals) formed in cells following irradiation (Alper, 1979). The physicochemical nature of the “oxygen effect” became evident from the studies of Johansen and Howard-Flanders (1965) on radiation-induced cell killing in bacteria. They demonstrated a “radioprotectable” fraction of damage which could be deduced from the competitive reactions of the target molecule and a radioprotector with the hydroxyl radical (OH) but not with the hydrogen radical or hydrated electron. The hydroxyl radical was therefore implicated as the major determinant in the radiation-induced cell killing by direct action. |
