Question

Biochemistry 3. What is the Bohr effect ? How does Hemoglobin Transport O2, and how to regulate the transportation by pH and 2,3 BPG in the lungs and tissues, respectively?

Answer 1

The Bohr Effect refers to the observation that increases in the carbon dioxide partial pressure of blood or decreases in blood pH result in a lower affinity of hemoglobin for oxygen.

Hemoglobin, or Hb, is a protein molecule found in red blood cells made of four subunits: two alpha subunits and two beta subunits. Each subunit surrounds a central heme group that contains iron and binds one oxygen molecule, allowing each hemoglobin molecule to bind four oxygen molecules. Molecules with more oxygen bound to the heme groups are brighter red. It is easier to bind a second and third oxygen molecule to Hb than the first molecule. This is because the hemoglobin molecule changes its shape, or conformation, as oxygen binds. As the partial pressure of oxygen increases, the hemoglobin becomes increasingly saturated with oxygen.

An increase in tissue PCO2 leads to an increase in hydrogen ion (H+) concentration that leads to a decrease in pH. Together, these effects will lead to a decrease in the affinity of hemoglobin to oxygen and cause the shift of the hemoglobin dissociation curve to the right. Specifically, it is the association of protons (H+ ions) with the amino acids in hemoglobin that tend to reduce the affinity for oxygen. The protons shift the configuration of the amino acids to the T-form, reducing attraction for oxygen.

When 2,3-BPG binds to deoxyhemoglobin, it acts to stabilize the low oxygen affinity state (T state) of the oxygen carrier. ... This release is potentiated by the Bohr effect, in which hemoglobin's binding affinity for oxygen is also reduced