THE ROLE OF THIOL GROUPS IN THE DEVELOPMENT OF RADIATION DAMAGE IN THYMOCYTES AND EHRLICH ASCITES CARCINOMA CELLS

The Biochemical Effects of Ionizing Irradiation on Nuclear Function in Animal Cells

This discussion of the biochemical lesions produced in animal cells by ionizing radiation will to all intents and purposes be restricted to a consideration of the immediate response to doses of 1000 rads or less in two rat tissues only, namely the thymus gland and the regenerating liver. The experiments we have carried out with these two tissues have led us to the view that in these organs the ultimate damage to the cell stems from an initial upset of the nuclear thiol-disulphide equilibrium.

Acid-soluble sulfhydryl compounds in L-cells during various conditions of growth

During exponential growth of suspension cultures of L-cells, the intracellular concentration of acid-soluble sulfhydryl compounds varied in a characteristic fashion. In a freshly diluted culture, the concentration rose to a maximum but as the population density increased, the concentration fell. This effect was attributed to inadequate cultural conditions; either a needed substance became limiting or an undesirable substance accumulated. Thus, if the culture was diluted frequently to approximate chemostatic conditions, the concentration remained at a high and constant level. When cell division was inhibited by 5-fluorodeoxyuridine, the level of acid-soluble sulfhydryl compounds increased but the extent of the increase again depended on the age of the culture, with a freshly diluted culture showing a maximum increase. Several other cellular constituents as well as the cellular volume also exhibited these patterns. The major sulfhydryl and disulfide components in the cell were reduced and oxidized glutathione. Only traces of cysteine and two unidentified sulfhydryl compounds were present. Cell growth in medium lacking glutathione was completely normal. In addition, the cysteine in the medium was found to be completely oxidized. Thus, the cells have mechanisms which enable them to obtain their cysteine requirements from the cystine in the medium, to synthesize glutathione de novo, and to maintain a reduced-plus-oxidized glutathione balance and at the same time maintain a very small pool of cysteine and (or) cystine.