Sulfhydryl Groups and the Oxygen Effect on Irradiated Dilute Solutions of Enzymes and Nucleic Acids

DNA irradiated in cells has previously been shown to be more sensitive in the presence of oxygen. It is shown that enzymes in cells are similarly three times as radiosensitive under oxygenated conditions. A paradox then arises, since dilute solutions of enzymes and of DNA have been repeatedly shown to be without an oxygen effect, yet much of the radiation inactivation in a cell is caused by radical attack. It is shown that the radiosensitivity of DNA in preparations of lysed cells is oxygen-dependent. Furthermore, dilute solutions of DNA and of trypsin show an oxygen effect when SH-containing compounds are added. Possible mechanisms for the oxygen effect are discussed in light of these results. (auth)