Which of the following hemoglobins is insoluble under lowered oxygen tension?

The hemoglobin that is insoluble under lowered oxygen tension is Hb-S, which is sickle hemoglobin associated with sickle cell disease. In conditions of low oxygen levels (hypoxia), Hb-S tends to polymerize, leading to the distortion of red blood cells into a characteristic sickle shape. This process significantly reduces the solubility of Hb-S compared to other forms of hemoglobin.

When oxygen levels are normal, Hb-S can dissolve in the blood, but as oxygen tension decreases, the red blood cells that contain Hb-S can aggregate and form rigid structures, contributing to the complications associated with sickle cell disease. This unique characteristic of Hb-S is central to understanding the pathophysiology of the disease, as it leads to increased blood viscosity, vaso-occlusive crises, and other clinical manifestations.

In contrast, hemoglobins such as Hb-A (normal adult hemoglobin), Hb-F (fetal hemoglobin), and Hb-C (an abnormal hemoglobin variant) do not exhibit the same level of insolubility under low oxygen conditions as Hb-S does. Each of these hemoglobins behaves differently in physiological and pathological states, but they do not precipitate and cause red cell sickling as prominently as Hb-S when oxygen levels