Bohr effect

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Oxyhaemoglobin Dissociation Curve. Dotted red line corresponds with shift to the right caused by Bohr effect.

The Bohr effect is a property of hemoglobin first described by the Danish physiologist Christian Bohr in 1904. Because of the Bohr effect, an increase in blood carbon dioxide level, a decrease in pH or increased temperature causes hemoglobin to bind to oxygen with less affinity.

This effect facilitates oxygen transport as hemoglobin binds to oxygen in the lungs, but then releases it in the tissues, particularly those tissues in most need of oxygen. When a tissue's metabolic rate increases, its carbon dioxide production increases. The carbon dioxide is quickly converted into bicarbonate molecules and acidic protons by the enzyme carbonic anhydrase:

CO₂+ H₂O → H⁺ + HCO₃⁻

This causes the pH of the tissue to decrease, and so increases the dissociation of oxygen from hemoglobin, allowing the tissue to obtain enough oxygen to meet its demands.

The dissociation curve shifts to the right when carbon dioxide concentration, temperature, or hydrogen ion concentration is increased. This facilitates increased oxygen dumping. This makes sense because increased CO₂ concentration and lactic acid build-up occur when the muscles need more oxygen. Changing hemoglobin's oxygen affinity is the body's way of adapting quickly to this problem.

In the Hiroshima variant hemoglobinopathy the Bohr effect is diminished so the hemoglobin has a higher affinity for oxygen and tissue may suffer minor oxygen starvation during high work.