HEMOGLOBIN Hemoglobin is a globular protein and it is a roughly spherical molecule found in red blood cells, where its primary function is to transport oxygen from the lungs to every tissue in the body. Because of subunit interactions, the oxygen dissociation curve of hemoglobin has a sigmoidal shape.As the first O2 binds to hemoglobin, the binding of additional O2 to the same molecule is enhanced.This binding pattern, called cooperative binding, results from changes in hemoglobin's three-dimensional structure that are initiated when the first O2 binds.The binding of the first O2 facilitates the binding of the remaining three O2 molecules to the tetrameric hemoglobin molecules. In the lungs, where O2 tension is high, hemoglobin is quickly saturated(its R state). In tissues depleted of O2,hemoglobin gives up about half of its oxygen. The binding of ligands other than oxygen affects hemoglobin's oxygen-binding properties. For example, the dissociation of oxygen from hemoglobin is enhanced if pH decreases.By this mechanism called Bohr effect, oxygen is require large amounts of the waste product CO2.As CO2 diffuses into blood,it reacts with water to form hydronium ion and hydrogen ion.The subsequent binding of hydrogen ion to several ionizable groups on hemoglobin molecules enhances the dissociation of O2 by converting hemoglobinto its T state.(Hydrogen ions bind prefentially to deoxyHb.Any increase in hydrogen concentration stabilizes the deoxy conformotion of the protein and therefore speeds its formation).When a small number of CO2 molecules bind to terminal amino groups on hemoglobin,forming carbamate, the deoxy form (T state) of the protein is additionally stabilized. 2,3-Bisphosphoglycerate (BPG) is also an important regulator of hemoglobin function.Although most cells contain only trace amounts of BPG, red blood cells contain a considerable amount.BPG is derived from glycerate-1,3-biphosphate, an intermediate in the breakdown of the energy-rich compound glucose.In the absence of BPG, hemoglobin has a very high affinity for oxygen.As with hydrogen ion and CO2,binding BPG stabilizes deoxyHb.A negatively charged BPG molecule binds in a central cavity within hemoglobin that is lined with positively charged amino acids. In the lungs,the process is reversed.A high oxygen concentration drives the conversion from the deoxyHb configuration to that oxyHb.The change in the protein's three-dimensional structure initiated by the binding of the first oxygen molecule releases bound CO2,hydogen ion, and BPG.The hydrogen ion recombine with carbonium ion to form carbonic acid, which then dissociates to form CO2 and H2O.CO2 subsequently diffuses from the blood into the alveoli.
HEMOGLOBIN Hemoglobin is a globular protein and it is a roughly spherical molecule found in red blood cells, where its primary function is to transport oxygen from the lungs to every tissue in the body.
Because of subunit interactions, the oxygen dissociation curve of hemoglobin has a sigmoidal shape.As the first O2 binds to hemoglobin, the binding of additional O2 to the same molecule is enhanced.This binding pattern, called cooperative binding, results from changes in hemoglobin's three-dimensional structure that are initiated when the first O2 binds.The binding of the first O2 facilitates the binding of the remaining three O2 molecules to the tetrameric hemoglobin molecules. In the lungs, where O2 tension is high, hemoglobin is quickly saturated(its R state). In tissues depleted of O2,hemoglobin gives up about half of its oxygen.
The binding of ligands other than oxygen affects hemoglobin's oxygen-binding properties. For example, the dissociation of oxygen from hemoglobin is enhanced if pH decreases.By this mechanism called Bohr effect, oxygen is require large amounts of the waste product CO2.As CO2 diffuses into blood,it reacts with water to form hydronium ion and hydrogen ion.The subsequent binding of hydrogen ion to several ionizable groups on hemoglobin molecules enhances the dissociation of O2 by converting hemoglobinto its T state.(Hydrogen ions bind prefentially to deoxyHb.Any increase in hydrogen concentration stabilizes the deoxy conformotion of the protein and therefore speeds its formation).When a small number of CO2 molecules bind to terminal amino groups on hemoglobin,forming carbamate, the deoxy form (T state) of the protein is additionally stabilized.
2,3-Bisphosphoglycerate (BPG) is also an important regulator of hemoglobin function.Although most cells contain only trace amounts of BPG, red blood cells contain a considerable amount.BPG is derived from glycerate-1,3-biphosphate, an intermediate in the breakdown of the energy-rich compound glucose.In the absence of BPG, hemoglobin has a very high affinity for oxygen.As with hydrogen ion and CO2,binding BPG stabilizes deoxyHb.A negatively charged BPG molecule binds in a central cavity within hemoglobin that is lined with positively charged amino acids.
In the lungs,the process is reversed.A high oxygen concentration drives the conversion from the deoxyHb configuration to that oxyHb.The change in the protein's three-dimensional structure initiated by the binding of the first oxygen molecule releases bound CO2,hydogen ion, and BPG.The hydrogen ion recombine with carbonium ion to form carbonic acid, which then dissociates to form CO2 and H2O.CO2 subsequently diffuses from the blood into the alveoli.
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