[Effect of sheep haptoglobin on the hemoglobin molecule in the Hp-Hb complex]

Abstract

Sheep haptoglobin (HpC) binding hemoglobin increases the stability of the latter to acid denaturation and oxidation by atmospheric O2. HpC is also capable of binding methemoglobin (MetHb) denaturated at pH 3.5 to form a stable complex. This process is accompanied by partial reconstitution of the structural integrity and peroxidase activity of MetHb. Consequently, the formation of a HpC-MetHb complex leads to changes in the tertiary structure of the MetHb molecule. The increase in the peroxidase activity of MetHb at pH less than or equal to 4.0 after its binding to HpC is due to the stabilizing and stimulating activity of HpC.