Hoofdstuk 9: Hemoglobine en Myoglobine
➢ Hemoglobin
♥ Transport of O2 from lungs to tissue
♥ Transport of CO2 from tissue to lungs
♥ binding is cooperative; when one O2 is bound, it becomes easier for the next O2 to bind
♥ Allosteric protein: binding of O2 in one subunit brings changes in structure of other subunit(s)
♥ Structure:
♪ tetramer of two α-chains (141 amino acids each) and two β- chains (153 amino acids each); α2β2
♪ α- and β-subunits have 3D- structures that are similar to that of myoglobin
♪ each chain has one heme group; hemoglobin can bind up to 4 molecules of O2
♪
♥ oxygen or CO binding
♪ Adjacent subunits' affinity for oxygen increases
♪ This is called positive cooperativity
♪ This does not happen in Myoglobin
♪ If Hemoglobin behaved like Myoglobin, very little oxygen would be released in capillaries
♪ The sigmoid, cooperative oxygen binding curve of Hemoglobin makes this possible!
♪ Regulation of oxygen binding/release
❖ 2,3-Bisphosphoglycerate (2,3-BPG)
• Highly anionic compound
• Present in red blood cells at ~same concentration as hemoglobin
• 2,3-BPG binds at a site distant from the Fe where oxygen binds (the middle gap between subunits)
allosteric effector
•
• Affinity to oxygen less, which means more oxygen release in tissues
, ❖ The Bohr Effect
• The effect of pH on the oxygen-binding ability of Hb is called the Bohr effect
•
as pH decreases (more acidic), oxygen is released
○
• With PH decrease, T state is stabilized because histidine becomes protonated and binds with aspartate
❖ CO2 regulation
• CO2 promotes release of O2 from HbO2
• Binds to N-termines of hemoglobin
➢ Hemoglobin
♥ Transport of O2 from lungs to tissue
♥ Transport of CO2 from tissue to lungs
♥ binding is cooperative; when one O2 is bound, it becomes easier for the next O2 to bind
♥ Allosteric protein: binding of O2 in one subunit brings changes in structure of other subunit(s)
♥ Structure:
♪ tetramer of two α-chains (141 amino acids each) and two β- chains (153 amino acids each); α2β2
♪ α- and β-subunits have 3D- structures that are similar to that of myoglobin
♪ each chain has one heme group; hemoglobin can bind up to 4 molecules of O2
♪
♥ oxygen or CO binding
♪ Adjacent subunits' affinity for oxygen increases
♪ This is called positive cooperativity
♪ This does not happen in Myoglobin
♪ If Hemoglobin behaved like Myoglobin, very little oxygen would be released in capillaries
♪ The sigmoid, cooperative oxygen binding curve of Hemoglobin makes this possible!
♪ Regulation of oxygen binding/release
❖ 2,3-Bisphosphoglycerate (2,3-BPG)
• Highly anionic compound
• Present in red blood cells at ~same concentration as hemoglobin
• 2,3-BPG binds at a site distant from the Fe where oxygen binds (the middle gap between subunits)
allosteric effector
•
• Affinity to oxygen less, which means more oxygen release in tissues
, ❖ The Bohr Effect
• The effect of pH on the oxygen-binding ability of Hb is called the Bohr effect
•
as pH decreases (more acidic), oxygen is released
○
• With PH decrease, T state is stabilized because histidine becomes protonated and binds with aspartate
❖ CO2 regulation
• CO2 promotes release of O2 from HbO2
• Binds to N-termines of hemoglobin
