On the Chemical Basis of the Biological Actions of Ionizing Radiations

Abstract

Water, present in irradiated biological systems may modify the radiation effects, compared, with dry solids, both in direct and in indirect action. The possible role of solvated electrons in such reactions are discussed. Model systems are described in which, without the assumption of energy transfer, theaction of ionizing radiations is concentrated on suitable acceptors present in low concentration (e.g. 10-'s M ferricyanide or cytochrome C) in the presence of up to 20% gel-forming protein, e.g, gelatine. Oxygen effects are described.Chemical changes are responsible for the observed biological effects of ionizing radiations. An understanding of the basic chemical effects of radiations on the component parts of a biological system may lead to an understanding of radiation biology. Biological systems are usually much more complex than the relatively simple chemical .model systems which have been studied in detail. Confusion, rather than better understanding, may result from the application of too simple explanations derived from radiation chemistry. Indeed, it is very likely that depending on the particular specific biological action studied, different chemical mechanisms may operate at different total doses and in different target areas of the living body.Because of this more complicated situation, the exact mechanism of the biological action of ionizing radiations in specific cases is not yet well understood. On the other hand, advances in the last few years in our understanding of radiation chemsitry have led to the establishment of what appears to be clear-cut mechanisms in a number of systems, and aqueous systems in particular. If applied with sufficient caution these advances in radiation chemistry may assist in understanding radiation biology. 'In the following, some of these advances, particularly in the radiation chemistry of aqueous systems will be surveyed. Biological systems are aqueous systems. Different kinds of aqueous systems: .dilute solutions, concentrated solutions,

Interaction Between Tyrosine and Divalent Sulfur in Fluorescence Quenching and in the Photochemistry of Ribonuclease

“…This would consist of the dissociation of an electron from the excited state of tyrosine within the protein. This type of process has been well substantiated in the photochemical formation of solvated electrons from excited states of organic anions [27,28]. However, a reaction path involving as a first step electron ejection would lead to immediate deactivation of tyrosine and electron capture by the S-S group in a later step would then not account for the decrease in fluorescence of the tyrosine residue.…”