Enzymatic reduction of hemoglobins M Milwaukee-1 and M Saskatoon by NADH-cytochrome b5 reductase and NADPH-flavin reductase purified from human erythrocytes.

Enzymatic reduction of the hemoglobin (Hb) M group was studied. Hb M Milwaukee-1 and Hb M Saskatoon were reduced by NADH-cytochrome b5 reductase highly purified from human erythrocytes. Hb M Saskatoon was also reduced by another enzyme in red cells, NADPH-flavin reductase. The reduction rates of Hb M Saskatoon by both enzymes were almost the same as those of MetHb A. The reduction of Hb M Milwaukee-1 by NADH-cytochrome b5 reductase progressed much more slowly than that of Hb M Saskatoon and MetHb A. It took 1/2 h and 10 h for the 50% reduction of Hb M Saskatoon and Hb M Milwaukee-1, respectively. These two methemoglobin reductases from erythrocytes did not reduce other hemoglobins M such as Hb M Iwate, Hb M Boston, or Hb M Hyde Park. A possible role of these abnormal hemoglobins as oxygen carriers and the reason for cyanosis in the patients of Hb M Saskatoon and Hb M Milwaukee-1 are discussed.