Effect of 3-amino-1,2,4-triazole on catalase and formation of methemoglobin from oxyhemoglobin in erythrocyte by superoxide radicals.

Abstract

The formation of methemoglobin (metHb) from HbO2 in the [rat] erythrocyte by O2- was studied under the O2--generating system of photoactivated riboflavin with O2 by using a catalase inhibitor, 3-amino-1,2,4-triazole (AT). In the AT-treated erythrocytes in vitro, which have little catalase activity, the rate of metHb formation was increased remarkably compared with that of untreated normal erythrocyte. Catalase added to 60 unit/ml of the suspending medium contained AT-treated erythrocytes and caused a strong inhibition of formation of metHb, suggesting that H2O2 is generated in the external medium of erythrocytes by the reaction of photoactivated riboflavin or spontaneous dismutation of O2-. Addition of superoxide dismutase (5 .mu.g/ml) caused an acceleration but not inhibition of the metHb formation. Hemolysis was scarcely observed in the time-course of this experiment. Hydrogen peroxide generated in the outside of cells may move across the membrane and result in oxidative attack to HbO2 in the erythrocyte without the hemolytic effect. Another possible participation of O2- may be suggested to exert its enhanced oxidation of HbO2, i.e., that O2- generated in the outside of cells may pass through the membrane directly.