Reciprocal interactions between oxygen-binding and aquo-ferric chains in partially oxidized human hemoglobin A1

The concomitant changes in oxygen binding by ferrous hemes and in oxygenation-linked difference in absorbance of ferric hemes at 630 nm were studied at pH 6.8 in human partially oxidized hemoglobin A (Hb++/+++). At concentrations of ferric hemes less than 20% no changes in P50 of oxygenation were noted in comparison to the P50 value of Hb A. An increase of ferric hemes from 20 to 80% resulted in a parallel increase in oxygen affinity of functional hemes. Prevalence of alpha chains among the oxidized chains was confirmed in the studied Hb++/+++ containing less than 20% of ferric hemes. The oxygenation linked increases in absorbance of ferric hemes at 630 nm were related in a linear fashion to the increase in the ferric hemes content fom 0 to 40%. The lack of change in oxygen affinity of HB++/+++ containing less than 20% of ferric hemes, which exhibits the oxygenation-linked changes in absorbance of ferric hemes may be related to the presence and properties of asymmetric tetramers alpha+++ alpha++ beta 2++.