Oxygen dissociation curve characteristics of common hemoglobin variants and its potential implications: A brief report

Objectives: Hemoglobin E and S (HbE and HbS) are the most common hemoglobin (Hb) variants widely spread across the Asian continent that differ from the normal adult Hb in a single amino acid in the β-globin gene. The aim of this study was to explore if this change in globin structure has any effect in the function of Hb in terms of its oxygen affinity. Material and Methods: The oxygen dissociation curve (ODC) describes the relationship between the partial pressure of oxygen (pO2) and oxygen saturation of hemoglobin (sO2). ODC was plotted based on pO2 and sO2 values obtained on bubbling buffered oxygen and nitrogen gases through reconstituted variant Hb mixture samples in an experimental setup. Results: The p50 values of fetal hemoglobin (HbF), HbA, HbE, Sbeta, and HbS were found to be 20 ± 2 mmHg, 28.01 ± 2.5 mmHg, 33 ± 1.5 mmHg, 38 ± 2 mmHg, and 40± 0.6 mmHg at a pH of 7–7.5 and ambient temperature of 25°C, respectively. Conclusion: HbF had greater oxygen affinity while HbE and HbS showed a decreased oxygen affinity, more pronounced with HbS, possibly due to shift in the equilibrium toward the deoxy form. Even though the clinical implication may be variable, these findings reflect that there could be an interplay between Hb variants and oxygen affinity.