Correlation between the Radiobiological Oxygen Constant, K , and the Non-protein Sulphydryl Content of Mammalian Cells

The value of the radiobiological oxygen constant K has been found to depend on the concentration of non-protein sulphydryl (NPSH) within the cell. Cells in the exponential phase of growth have a higher concentration of NPSH and a higher value of K than cells in plateau phase. Binding NPSH with N-ethylmaleimide reduced the value of K and conversely, addition of NPSH as dithioerythritol increased the value of K. K also rises with the same time course as NPSH increases, when plateau phase cells are replated into fresh medium. These results support the hypothesis that free-SH groups within the cell compete with oxygen to react with radiation damaged molecules.