Protons Arise From Rupture of Salt Bonds When O2 Binds

Protons responsible for the Bohr effect arise from rupture of salt bridges during the binding of O2 to T state

- Exhaled

CARBONIC ANHYDRASE

2H2CO3 k

PERIPHERAL TISSUES

PERIPHERAL TISSUES

2H2CO3 I

LUNGS

2H2CO3 I

CARBONIC ANHYDRASE

2CO2 + 2H2O

Generated by-the Krebs cycle

Figure 6-9. The Bohr effect. Carbon dioxide generated in peripheral tissues combines with water to form carbonic acid, which dissociates into protons and bicarbonate ions. Deoxyhemoglobin acts as a buffer by binding protons and delivering them to the lungs. In the lungs, the uptake of oxygen by hemoglobin releases protons that combine with bicarbonate ion, forming carbonic acid, which when dehydrated by carbonic anhydrase becomes carbon dioxide, which then is exhaled.

hemoglobin. Conversion to the oxygenated R state breaks salt bridges involving P-chain residue His 146. The subsequent dissociation of protons from His 146 drives the conversion of bicarbonate to carbonic acid (Figure 6-9). Upon the release of O2, the T structure and its salt bridges re-form. This conformational change increases the pK of the P-chain His 146 residues, which bind protons. By facilitating the re-formation of salt bridges, an increase in proton concentration enhances the release of O2 from oxygenated (R state) hemoglobin. Conversely, an increase in PO2 promotes proton release.

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