The Inactivation of SH Enzymes by x-rays

Summary

The susceptibility of SH-enzymes to the indirect effect of ionizing radiation has been re-investigated. The claims of previous authors that these enzymes are particularly radiosensitive could not be confirmed. Dilute solutions of crystalline glyceraldehyde-3-phosphate dehydrogenase and yeast alcohol dehydrogenase were found to be inactivated by x-rays, with ionic yields of about 0·02. In contrast to previous reports no reactivation was obtained by the addition of reduced glutathione after the irradiation.

The discrepancy between the present results and those of earlier investigators can in part be explained by the fact that the earlier estimations of ionic yields were based on molecular weights for the enzymes which differ by a factor of about 2 from those currently accepted. The present data seem to be consistent with a number of radiochemical and enzymological findings.