The Radiosensitizing Effect of Thioglycolic Acid, Dithiodiglycolic Acid, and Homocystine on Muscle Glyceraldehyde-3-phosphate Dehydrogenase

Summary

It is demonstrated that thioglycolic acid and its disulphide, dithiodiglycolic acid, as well as homocystine, have a pronounced radiosensitizing effect on the x-ray inactivation of crystalline rabbit-muscle glyceraldehyde-3-phosphate dehydrogenase in solution. A number of other thiols and disulphides tested exert a protective effect.

The radiosensitization observed is associated with a disappearance of free enzyme SH-groups, and it can be reversed by addition of excess thiols after the radiation exposure. The data indicate that the sensitizing mechanism involves a blocking of essential enzyme SH-groups through a radiochemical formation of mixed disulphides between the enzyme SH-groups and the radiosensitizing substances.