HEME STABILITY IN THE HUMAN EMBRYONIC HEMOGLOBINS

The three human embryonic hemoglobins undergo both monomolecular and n ucleophile stimulated bimolecular oxidations. Azide acts as an efficie nt nucleophile for the oxidative process in which the three embryonic hemoglobins exhibit lower oxidation rates than the adult protein. The absolute rates of azide-induced oxidation together with the rates of s pontaneous autooxidation correlate with the previously determined oxyg en affinities of the embryonic hemoglobins. The pH dependence of the r ates of oxidation and their chloride ion concentration dependence are discussed. Heme exchange to human serum albumin has been used to deter mine the relative binding constants for heme for each of the embryonic proteins. Rate data have also been employed to evaluate the tetramer- dimer equilibrium constant for each hemoglobin. Overall, the data indi cate that the high oxygen affinity human embryonic hemoglobins are sig nificantly less susceptible to anion-induced oxidation, and the heme g roups in each of the embryonic globin proteins are more tightly bound than in the corresponding adult protein.