Studies on the mechanism of action of ionizing radiations; inhibition of sulfhydryl enzymes by alpha, beta, and gamma rays.

The activity of crystalline phosphoglyceraldehyde dehydrogenase and urease was decreased when dilute solutions of these sulfhydryl enzymes were irradiated with small doses of alpha rays from Po, beta rays from Si(89), and gamma rays from Ra. Partial reactivation of the enzyme by addition of glutathione was obtained after inhibition with alpha rays. Evidence that these inhibitions are due to oxidation of the -SH groups of the enzymes was given by the irradiation of the mercury-mercaptide urease with gamma rays.

Studies on the mechanism of action of ionizing radiations; inhibition of enzymes by X-rays.

Dilute solutions of sulfhydryl enzymes (phosphoglyceraldehyde dehydrogenase, adenosinetriphosphatase, succinoxidase) showed reduced activity on irradiation by small amounts of x-rays. When the inhibition was partial the enzyme was reactivated on addition of glutathione. When the inhibition was more complete, reactivation was only partial.