[Dependence of human erythrocyte methemoglobin reductase on temperature]

The effect of temperature on the activities of cytoplasmic and membrane-bound fractions of NADH-cytochrome beta 5 reductase on the total activity of methemoglobin reductase in intact human erythrocytes was studied within the temperature range of 20-50 degrees C. The above three activities showed a break in the Arrhenius plots at 42 degrees C which was attributed to irreversible inactivation of the enzymes. Thermal inactivation of methemoglobin reductase in erythrocytes was found to increase the methemoglobin content concomitantly with a decrease in the osmotic stability and activation of spontaneous cell hemolysis.