¹ From the Department of Pathological Chemistry, University of Toronto, Toronto, Canada, and The Rockefeller Institute for Medical Research, New York

The x-irradiation of a dilute suspension of erythrocytes results in a decrease in the glyoxalase activity of the cells as a result of a fall in the reduced glutathione level. The present paper deals with the possible role of H₂O₂ in this reaction.

The addition of intact erythrocytes to physiological saline previously irradiated with 150,000 r or 225,000 r results in a fall in the glyoxalase activity of the cells. The inhibition is prevented by the preincubation of the irradiated saline with catalase and is reversed by the addition of plasma, glucose, adenosine, and inosine to the cell suspension.

An inhibition of the glyoxalase activity is also produced by the addition of H₂O₂ to the suspension of erythrocytes. The inhibitory effect of H₂O₂ can be prevented and largely reversed by plasma, glucose, adenosine, and inosine. Methylglyoxal is also protective under these conditions.

Hydrogen peroxide formed continuously and in low concentrations by enzyme systems appears to be more effective than added H₂O₂ in inhibiting the glyoxalase system. The inhibition by H₂O₂-producing enzyme systems is minimized by the addition of catalase, plasma, glucose, methylglyoxal, and to a lesser extent, by adenosine and inosine, and is accentuated by the addition of sodium azide.

The results are discussed in relation to the role of H₂O₂ and catalase in the toxicity of ionizing radiations.

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