Hb Helsinki HbH is a hemoglobin mutant in which the lysine r

Hb Helsinki (HbH) is a hemoglobin mutant in which the lysine residue at position 82 has been replaced with methionine. The mutation is in the beta chain, and residue 82 is found in the central cavity of hemoglobin. The oxygen binding curves for normal adult hemoglobin (HbA, and HbH at pH 7.4 in the presence of a physiological concentration of 2, 3BPG are shown in the graph Explain why the curve for HbH is shifted from the curve for HbA. Does this mutation stabilize the R or T state? What result does this mutation have on oxygen affinity?

Solution

HbH value suggests that the curve is left shifted when compared with the HbA, because HbH has a higher oxygen affinity. The explanation for this is the reduced binding of 2,3 diphosphoglycerate (2,3 DPG) to HbH haemoglobin. 2,3 DPG binds far better the beta chains of HbA haemoglobin and this shifts the curve to the best indicating a decrease in oxygen affinity. Actually, 2,3 DPG binds most avidly to the beta chains of deoxyhaemoglobin. HbH haemoglobin consists of 2 alpha chains and 2 gamma chains and do not have no beta chains. Consequently the value is lower than that of HbA haemoglobin because Hb is less sensitive to the effects of 2,3 DPG. (2,3-DPG) binds to deoxyhemoglobin with larger bonding affinity, such so it makes the T state of hemoglobin protein more stable or increases oxygen affinity of the protein.