Question

How does the change in pH from 7.2 to 8.2 affect the binding of BPG to the central cavity of Hemoglobin's T state? Is it no effect, increase or decrease binding? Explain why.

Answer 1

Answer:

As pH changes from 7.2 - 8.2 Oxygen release decreases hence BPG binding also decrease.

Explaination:

2,3-Bisphosphoglyceric acid (conjugate base 2,3-bisphosphoglycerate) (2,3-BPG), , is a three-carbon isomer of the glycolytic intermediate 1,3-bisphosphoglyceric acid (1,3-BPG). 2,3-BPG is present in human red blood cells . It binds with greater affinity to deoxygenated hemoglobin (e.g. when the red blood cell is near respiring tissue) than it does to oxygenated hemoglobin (e.g., in the lungs), but not as well in the oxygenated . It interacts with deoxygenated hemoglobin beta subunits by decreasing their affinity for oxygen, so it allosterically promotes the release of the remaining oxygen molecules bound to the hemoglobin, thus enhancing the ability of RBCs to release oxygen near tissues that need it most. 2,3-BPG is thus an allosteric effector.

Its function was discovered in 1967 by Reinhold Benesch and Ruth Benesch.

When 2,3-BPG binds to deoxyhemoglobin, it acts to stabilize the low oxygen affinity state (T state) of the oxygen carrier. It fits neatly into the cavity of the deoxy- conformation, exploiting the molecular symmetry and positive polarity by forming salt bridges with lysine and histidine residues in the ß subunits of hemoglobin. The R state, with oxygen bound to a heme group, has a different conformation and does not allow this interaction. By itself, hemoglobin has sigmoid-like kinetics, which makes easier another subunits’ binding (the first molecule of oxygen helps the following to link). As the pH level decreases, the affinity of oxygen in hemoglobin also decreases. Thus, as hemoglobin approaches a region of low pH, more oxygen is released

As carbon dioxide diffuses into red blood cells, it reacts with water inside to form carbonic acid. Carbonic acid disociated leads to lower pH and stabilizes the T state.