A comparison of the resistance of human and horse ferrihemoglobin to acid denaturation.

This research compares the resistance of human and horse ferrihemoglobin to acid denaturation, highlighting the differences in the denaturation rate, pH equilibrium, temperature effects, regeneration rate, and the presence of hidden groups. Notably, human ferrihemoglobin showed higher rates of denaturation and different regeneration kinetics.

Background

• This study primarily focuses on comparing the stability features of horse and human ferrihemoglobin (the oxidized form of hemoglobin) in acid solutions.

Key Findings

• A key difference observed in the human and horse proteins is the significantly quicker rate of denaturation in human protein at all pH levels.
• Further differences include a shift towards a higher pH in the balance between the native and acid-denatured forms, variations in the temperature at which the temperature’s impact on the balance and pH curve reverses.
• The human ferrihemoglobin lacked the dependence on the extent of denaturation for the rate of regeneration found in horse ferrihemoglobin.
• Finally, the human protein failed to follow the “inhibited regeneration model”, developed based on horse ferrihemoglobin studies.

pH-Stat Experiments and Rapid Flow Titration Curves

• The findings of the pH-stat experiments and rapid flow titration curves indicated that human ferrihemoglobin has about four more hidden groups, presumably imidazoles, compared to horse ferrihemoglobin.
• Both proteins were found to contain the same number of histidine residues. Despite regeneration, very little re-masking of these unmasked groups was observed unless a cyanide ligand was introduced.

Regeneration of Soret Band

• Regeneration, observed as the reappearance of the Soret band, a distinct absorption band of the heme group in hemoglobin, occurred readily.
• There was a noticeable difference in the speed of disappearance of the band at 370 mA, characteristic of denatured oxidized heme-protein complexes, versus the re-appearance of the Soret band.
• The findings showed a more marked discrepancy in human protein compared to horse protein.