Some Biochemical Consequences of the Spatial Distribution of Ionizing Radiation-Produced Free Radicals

Ionizing radiation deposits energy nonhomogeneously in the medium through which it passes. Mozumder and Magee (Radiat. Res. 28, 203-214 (1966)) have classified the events as spurs, blobs, and short tracks. These are defined by size and amount of energy deposited-a spur is 10 A in diameter and contains 2-3 ion pairs. Thus the initial chemically reactive species are distributed in an inhomogeneous manner. In these volumes of high radical concentration, radical-radical reactions can occur which can only be scavenged by solutes at high concentration. Making the reasonable assumption that similar events occur intracellularly, the consequences of such events must be considered. In the case of DNA, several authors have shown that· OH radicals diffuse only tens of angstroms prior to reaction (a distance of the same dimensions as spurs, etc.). In the volume from which these radicals originate, DNA is necessarily at high concentration and consequently will interact with the radicals formed in the spur, etc. Such ev...