[Regulation of methemoglobin reduction in human erythrocytes].

The regulation of methemoglobin reduction in human erythrocytes was studied in vitro in association with glycolytic reactions, by using hemolysates prepared from the nitrate-treated eryth rocytes. The results obtained are as follows; 1) The addition of cytochrome b5 to the reaction mixture containing fructose 1,6-diphosphate as the substrate for glycolysis caused a marked increase in the rate of methemoglobin reduction with a simultaneous increase of the level of 2,3-bisphosphoglycerate and a decrease in the rate of lactate formation. 2) The effect on these reactions of the antibody against the human erythrocyte NADHcytochrome b5 reductase, and a cross-over plot of the metabolite concentrations in the reaction mixture revealed that the methemoglobin reduction observed was catalyzed by that enzyme, and was coupled with the glycolytic pathway at the glyceraldehyde 3-phosphate dehydrogenase reaction to affect the level of 2,3-bisphosphoglycerate. 3) Essentially the same results were obtained with the reaction in which glucose 6-phosphate was used as the substrate of glycolysis. 4) The kinetic data obtained in vitro imply that under physiological conditions the rate of methemoglobin reduction firstly depends on the concentration of cytochrome b5 in the erythrocytes .