Question

H₁₄₆ of the β -chain of normal adult hemoglobin ends up in close proximity to D₉₄ on the same chain when oxygen is delivered to the tissues. In hemoglobin Hiroshima H₁₄₆ on the β -chain has been changed to a D through mutation.

a) What effect does this mutation have on oxygen binding by hemoglobin Hiroshima, compared to normal hemoglobin? Explain.

b) What effect does this mutation have on the Bohr Effect of this mutant hemoglobin? Explain.

Answer 1

Reason for the effect of Hiroshima hemoglobin (146 H mutated to D) mutation on the oxygen binding and Bohr effect.

Salt bridge interactions play an important role in the oxygen affinity of the hemoglobin. Thes interaction stabilizes the deoxy forms of the hemoglobin and lowes the binding of the oxygen. In Hiroshima hemoglobin (146 H mutated to D) salt bridge interaction between H 146 of beta chain and Lys 40 of the alpha chain gets affected. This shifting of the equilibrium from deoxy-hemoglobin toward oxy-hemoglobin diminished Bohr effect will be observed.

a.

Hiroshima hemoglobin (146 H mutated to D) will have more oxygen-binding capacity than Hiroshima hemoglobin and normal adult hemoglobin (figure 1).

b.

Bohr effect

Shifting of oxygen binding curve of normal hemoglobin (Hb) is more than Hiroshima hemoglobin and Hiroshima hemoglobin (146 H mutated to D). This shows diminished Bohr effect of Hiroshima when compared to normal Hb and bore effect will be more diminished in Hiroshima hemoglobin (146 H mutated to D) as compared to Hiroshima hemoglobin (figure 2).

Joony. PM 65 Pn7 00} py Adult Normal HB g PH₂6 .Phot Nonnal Hb .ph P# 6.5%) pa-6 Hiroshima AB 61998awrynxo of 6-5/ Garrowlyha O / Ó Hiroshima Hbl (146(H) →D) 100. 14 os Bohr effect : Effect of oxygenation of haemoglobio at different PM ralues haeme Oxygros binding of foot og diffet tupeng moglobin Figure. I Ifigure-2

In figure

Blue: Normal adult Hb

Red: Hiroshima Hb

Green: Hiroshima Hb (146 H is replaced with D)