lecture_13legge - The Bohr Effect Globins & Enzyme...

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1 Globins & Enzyme Catalysis 10/06/2009 The Bohr Effect Higher pH i.e. lower [H + ] promotes tighter binding of oxygen to hemoglobin and Lower pH i.e. higher [H+] permits the easier release of Lower pH i.e. higher [H+] permits the easier release of oxygen from hemoglobin ( )( ) + + + + xH O Hb O H O Hb 1 n 2 2 x n 2 Where n = 0, 1, 2, 3 and x 0.6 A shift in the equilibrium will influence the amount of oxygen binding. Bohr protons CO 2 Transport and The Bohr Effect Higher pH i.e. lower [H + ] (more basic) promotes tighter binding of oxygen to hemoglobin and Lower pH i.e. higher [H+] Where n = 0, 1, 2, 3 and x 0.6 A shift in the equilibrium will influence the amount of oxygen binding. Bohr protons () + + + + xH O Hb O H O Hb 1 n 2 2 x n 2 (more acidic) permits the easier release of oxygen from hemoglobin Origin of the Bohr Effect The T R transition causes the changes in the pK’s of several groups. The N-terminal amino groups are responsible for 20-30% of the Bohr effect. His146 β accounts for about 40% of the Bohr effect salt bridged with Asp 94 β . This interaction is lost in the R state. Networks of H bonds & • The T-state is shown above. •T R transition causes breakage of terminal interactions and changes in ionization states of His146 β and Val1 α (part of Bohr effect) Networks of H-bonds & ion pairs in T-state Look at the relation between pH and the p 50 values for oxygen binding. As the pH increases the p 50 value decreases, indicating the oxygen binding increases (opposite effect,when the pH decreases). At 20 torr 10% more oxygen is released when the pH drops from 7.4 to 7.2!! CO 2 + H 2 O H + + HCO 3 - The Bohr effect: Importance in transporting O 2 and CO 2 As oxygen is consumed CO 2 is released. Carbonic Anhydrase catalyzes this reaction in red blood cells. • 0.6H+ released for each O 2 binding •C O 2 + H 2 O H+ + HCO 3 -, catalyzed by carbonic anhydrase – main mode of elimination of CO 2 D-2,3-bisphosphoglycerate (BPG) BPG binds to Hb (deoxy state) and decreases the O 2 affinity and keeps it in the deoxy form.
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This note was uploaded on 02/22/2011 for the course BCHS 3304 taught by Professor Johnson during the Spring '08 term at University of Houston.

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lecture_13legge - The Bohr Effect Globins & Enzyme...

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