Oxidation and cross-linking of human hemoglobins by activated oxygen species

The effect of activated oxygen species on human hemoglobins was studied. All radicals induced polymerization in Hb A both intermolecular and by cross-linking of subunits (intramolecular). However, a system producing mainly superoxide ion gave the most important changes. An oxidation step is necessary to produce polymerization since in the case of cyanmet Hb A (where there is no possible oxidation) no polymerization occurs. The effect of O2- on blocked SH beta 93 Hbs or on the abnormal Hbs tested was practically identical to that on Hb A although their autoxidation rates were modified. Consequently the action of radicals is different from autoxidation processes and the modified residues in the abnormal hemoglobins are not involved in the action of superoxide ion on Hb. The kinetics of oxidation of Hb by H2O2 followed two steps: the first is the oxidation of oxy Hb to ferri Hb and the second is hemichrome formation. This last step is independent of the presence of H2O2 since it is not inhibited by catalase. The kinetics of oxidation to ferri Hb were of second order and the rate constant was found to be 16 M-1 sec-1.