Question

C. At 1M Nacl, it was discovered that the oxygen binding properties of both mutant and wild type hemoglobin are the same over a range of pH values and in the presence or absence of BPG. The presence of 1M NaCl with HbA, wild type, causes a rightward shift compared to HbA without salt. Giv effects of the LysàAsp mutation. e a suggestion as to how NaCl suppresses the

Answer 1

1. BPG [2,3-Bisphosphoglyceric acid or 2,3-bisphosphoglycerate]

• BPG is an allosteric effector.
• It is present in human red blood cells It binds with greater affinity to deoxygenated hemoglobin than it does to oxygenated hemoglobin . It interacts with deoxygenated hemoglobin beta subunits by decreasing their affinity for oxygen. Hence it allosterically promotes the release of the oxygen molecules bound to the hemoglobin enhancing their ability to release oxygen near tissues that require oxygen.

2. A rightward shift implies that the hemoglobin under study has a decreased affinity for oxygen. It is more difficult for hemoglobin to bind to oxygen (requiring a higher partial pressure of oxygen to achieve the same oxygen saturation). However, it is easier for the hemoglobin to release oxygen bound to it.

3. Previous analyses have shown that the low oxygen affinity is due to the possible disruption of salt bridges between aspartic acid and lysines. These changes that may lead to steric interference in oxygen binding by changing the β‐chain structure.

4. NaCL suppresses the effects of Lys Asp mutation

The observation that oxygen binding properties of both mutant and wild type haemoglobin are same, irrespective of pH concentration or presence or absence of BPG, implies that NaCL decreases the oxygen affinity of haemoglobin such that both of the aforementioned factors have no significant effect anymore