Sulfhydryl Groups in Radiation Damage

Abstract

Several lines of evidence indicate that radiation-induced oxidation of protein sulfhydryl groups play a role in the development of radiation damage. In all -SH enzymes so far studied the radiation inactivation in solution can largely be accounted for by destruction of sulfhydryl groups. Since sulfhydryl groups have different functions in different enzymes, the inactivation may be brought about by different mechanisms. The over-all yield of inactivation of sulfhydryl enzymes shows a wide range of variation, depending on the number of sulfhydryl groups in the enzyme, their function and their radiation sensitivity. The radiation sensitivity of protein -SH groups is parallelled by their reactivity towards chemical agents. The most reactive sulfhydryl groups which are capable of interacting with disulfides, are by and large oxidized by ionizing radiation with high G-values (0.7–1.8), while the less reactive sulfhydryl groups are generally oxidized at low yields. In certain cases the products of radiation oxidation of protein -SH groups can be reduced to sulfhydryl groups, indicating that disulfides were formed. Since the cells contain disulfide-reducing mechanisms, it is possible that damage to protein -SH groups can in part be repaired. Evidence of such a mechanism has been found in the case of erythrocytes.

Key Words:

• Enzyme inactivation
• ionizing radiation
• radiation damage
• radiation protection
• -SH enzymes
• sulfhydryl groups