Enzymatic reduction of hemoglobins M

Reductions of five species of hemoglobins (Hb1) M by two methemoglobin reductases and by ferredoxin and ferredoxin-NADP reductase were studied under anaerobic conditions. Abnormal chains of Hb M Milwaukee and Hb M Saskatoon were reduced by NADH-cytochrome b5 reductase (= NADH-methemoglobin reductase) highly purified from human erythrocytes. Hb M Saskatoon was also reduced by an another enzyme in red cells, NADPH-flavin reductase (= NADPH-methemoglobin reductase). All Hbs M with a beta chains anomaly such as Hb M Hyde Park, Hb M Saskatoon, and Hb M Milwaukee were reduced by ferredoxin and ferredoxin-NADP reductase. These three enzymatic reduction systems did not reduce Hbs M with an alpha chain anomaly such as Hb M Iwate and Hb M Boston. These differences in the reduction are discussed in relation to the redox potential of each abnormal chain in methemoglobin M.