Haldane effect

The Haldane effect (named after its first person who described it, John Scott Haldane ) describes the increased ability of oxygen- poor blood to absorb carbon dioxide . The Haldane effect means that where blood releases a lot of O ₂ to the tissue, it can also absorb a lot of CO ₂ from the tissue.

During internal respiration , O _{2 is} exchanged for CO ₂ in the capillaries . The transport of oxygen to the tissues in vertebrates is largely done by the protein hemoglobin , which is found in high concentrations in the erythrocytes . The erythrocytes also contain the enzyme carbonic anhydrase , which catalyzes the following equilibrium reaction:

${\displaystyle \mathrm {CO_{2}+H_{2}O\rightleftharpoons HCO_{3}^{-}+H^{+}} }$

The resulting hydrogen carbonate is released into the blood via the erythrocyte membrane as part of the Hamburger Shift ; By converting CO ₂ into hydrogen carbonate, the blood can transport considerably more CO ₂ than would be possible through the physical solution alone . Since it is an equilibrium reaction, the conversion is limited by the concentration of the products (hydrogen carbonate and protons ). The Haldane effect is explained by the fact that deoxygenation of hemoglobin removes products from their equilibrium so that the reaction can continue.

Protons

The deoxygenation of hemoglobin has an influence on its conformation : It shifts the equilibrium between relaxed form (R) and tense form (T) in favor of the T-shape. The T-form binds protons with greater affinity than the R-form, so that more protons are bound to hemoglobin.

Bicarbonate

The hydrogen carbonate can react with terminal amino groups of the hemoglobin to form carbamate groups :

The equilibrium of this reaction is more on the side of the carbamate groups in the T-form than in the R-form. Deoxygenation thus leads to increased binding of hydrogen carbonate to hemoglobin. However, the carbamate formation plays a subordinate role in explaining the Haldane effect compared to the withdrawal of protons.

Inversion in the lungs

The oxygenation of the hemoglobin in the lungs reverses the processes described: because the blood can no longer store as much CO ₂ , it is released.

See also

• Bohr effect

literature

• Randall, Burggren, French: Eckert: Animal Physiology. Verlag WH Freeman and Company, 5th ed. 2002
• Müller: Animal and Human Physiology. Springer Verlag, Berlin 2nd edition 2004