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BCHE 395-9 2013 Ligand Binding and Hemoglobin

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Unformatted text preview: e Stabilizing Ionic Contacts in the T- State (Deoxy- )… • Fig. 7-9 •  HisNdine HC3 of T- state hemoglobin has a higher pKa than normal (via inter- acNon with Asp FG1), and thus gets readily protonated •  Back at the lungs, return to the R- state ships HC3 back to its normal pKa, releasing the H+ as bicarbonate is converted back to carbon dioxide pH Effect on O2 Binding to Hemoglobin Bohr Effect –  H+ binds to several amino acid residues, notably His146 (HC3) in Hbβ –  Stabilizes T state and promotes O2 dissociaNon 2,3- Bisphosphoglycerate (BPG) Regulates O2 Binding •  Nega<ve heterotropic regulator of Hb funcNon •  Present at mM concentraNons in erythrocytes –  Produced from an intermediate in glycolysis (Ch 14) •  Small negaNvely charged molecule, binds to the posiNvely charged central cavity of Hb •  Stabilizes the T states 2,3- BPG binds to the Central Cavity of Hb T- State •  2,3 bisphosphoglycerate can bind in a small pocket in the center of the hemoglobin tetramer – but only to the T- state! •  The conformaNon change in the R- state closes up the internal “hole”, thereby excluding BPG from binding R- State 2,3- BPG...
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