Formation of denatured erythrocytes by exposure to a superoxide radical generating system of xanthine oxidase.

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Abstract
Exposure of rat erythrocytes to an O2--generating system of xanthine oxidase resulted in the formation of cells resistant to hypotonic hemolysis along with the degradation of Hb without evidence of hemolysis. Exposure of cells for 30 min to the xanthine oxidase system caused a shift of the Soret maximum at 415 to 405 nm with the disappearance of 3 isosbestic points. At this time, a large amount of dark brown pigment was formed in cells, and rigid cells resistant to hypotonic hemolysis were formed. Catalase, but not superoxide dismutase, strongly inhibited the oxidative degradation of HbO2 and the formation of resistant cells, suggesting possible involvement of H2O2 in the xanthine oxidase system. Cells exposed directly to H2O2 were transformed to resistant cells, but this did not occur in the presence of KCN. Denatured cells presumably are produced in association with the formation of methemoglobin and denatured Hb, which precipitates in the cells throughout the exposure period to H2O2 generated in the xanthine oxidase system.