Radiation damage and free radical production in irradiated ribonuclease.

It is probable that transient free radical states are implicated in the chain of events leading to the production of radiation damage. In solids and in dry biological materials, these free radicals are comparatively stable and have been studied by a number of workers in materials of biological interest, including biochemicals (1, 2), bacterial spores (3), and seeds (4, 5). The objective of such studies has been to determine the extent to which free radical mechanisms are responsible for the biological effects of ionizing radiation. Unfortunately, from the radiobiological point of view, many of the studies utilizing pure compounds have been limited by the lack of an assayable biological activity, and studies of radiation effects on biologically active systems are often difficult to interpret because of the complexity of the systems at the molecular level. Some of these difficulties may be avoided by using as a test system a biologically active macromolecule, either protein or nucleic acid. At the present time, the bestcharacterized of these macromolecules are the enzymes-in particular, the enzyme ribonuclease (RNase). In the experiments to be reported here, the radiation sensitivity of the enzymatic activity of RNase irradiated in the dry state in various gaseous environments has been studied, and a preliminary attempt has been made to relate these results to the electron spin resonance (ESR) spectra of the free radicals produced in dry RNase by radiation.