Reduction and spectroscopic properties of hemoglobins M

Reduction of five hemoglobins M (Hbs M) was studied using three enzymatic reducing systems; namely NADPH-flavin reductase from human erythrocytes, NADH-cytochrome b5 reductase from human erythrocytes and ferredoxin-NADP reductase from spinach. Under anaerobic conditions, abnormal chains in Hb M Saskatoon were reduced by all three systems, whereas those in Hb M Milwaukee were reduced by the latter two enzyme systems only. The abnormal chains in Hb M Hyde Park were reduced only by the ferredoxin-NADP reductase system. On the other hand, the abnormal chains in Hb M Iwate and Hb M Boston were reduced by sodium dithionite, but not by the three enzymatic reducing systems. Absorption and circular dichroic (CD) spectra of these Hbs M were compared with those of Hb A to examine their structural abnormalities. Absorption and CD spectra of four Hbs M except Hb M Milwaukee were remarkably different from those of Hb A. Conformational differences between alpha- and beta-abnormal Hbs M were reflected in the CD spectrum of the ultraviolet region. The difference between the proximal and distal histidine-replaced Hbs M was also observed in the CD spectra of the visible region.