Allosteric Property of Hemoglobin Explained
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Here's the positive and negative allosteric effectors of hemoglobin
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Allosteric Property of Hemoglobin Explained
- 2. CONTENTS Hemoglobin Allosteric property Homotropic effect Oxygen-Hb dissociation curve Heterotropic effect Conclusion
- 3. HEMOGLOBIN Found exclusively in red blood cells (RBC) Metallo-globular protein Composed of heme (a prosthetic group) and 4 globin polypeptide chains Function of Hb – transport of respiratory gases 20-30T of RBCs Carry 270M of Hb
- 4. HEME Iron containing porphyrin Porphyrins – complex compounds with a tetrapyrrole structure
- 5. HEME POCKET Heme pocket β – subunit is blocked by valine
- 6. GLOBIN 2 types of globin – α and β α – 141 amino acids, folded in 7 α helixes β – 146 amino acids, folded in 8 α helixes Hemoglobin tetramer - composed of two identical dimers, (αβ)1 and (αβ)2 574 amino acids α1 α2 β1 β2 Dimer 1 Dimer 2
- 8. Schematic diagram showing structural changes resulting from oxygenation and deoxygenation of hemoglobin
- 9. ALLOSTERIC EFFECT A protein that exhibits changes in ligand (substrate) affinity under the influence of small molecules (allosteric effectors) → Km decrease Protein – multisubunits Effectors – bind to sites that are spartially distinct from the ligand binding site E.g. Hb, key enzymes of the metabolic pathway Homotropic – an allosteric effector affect its own binding affinity Heterotropic – an allosteric effector is different from the ligand whose binding is altered
- 10. HEMOGLOBIN Homotropic effect Oxygen (positive allosteric effector) Heterotropic effect H+ (Bohr effect) CO2 2,3-BPG Negative allosteric effectors
- 13. Pulls the proximal His F8 F helix, EF corner, FG corner shifted Conformational changes -> dissolution of existing non covalent bonds and formation of new ones at the heterodimer interfaces α1 α2 β1 β2
- 14. POSITIVE COOPERATIVE EFFECT α 1 β 1 and α 2 β 2 dimers rotate approximately 15 degrees with respect to one another T to R form Binding of 1st O2 to one subunit facilitate the serial binding of O2 to remaining subunits Increasing affinity → Positive cooperative effect
- 15. Oxygen-Hb dissociation curve Flat upper part → blood loads O2 in spite of a large decrease in PO2 Steep middle and lower part → deliver more oxygen to the tissues in response to small changes in PO2 P50 → PO2 at which Hb is half saturated with O2 P50 α 1/affinity
- 16. Bohr Effect The release of oxygen from hemoglobin is enhanced when the pH is lowered or when the hemoglobin is in the presence of an increased pCO2 The deoxy form of hemoglobin has a greater affinity for protons than does oxyhemoglobin. An increase in the concentration of protons → protonated → able to form ionic bonds (salt bridges) → stabilize the T form of hemoglobin → decrease in oxygen affinity
- 17. Oxygen-Hb dissociation curve Shift the curve to the right Permits efficient unloading of O2 to the tissues
- 18. 2,3-Bisphosphoglycerate RBC glycolysis → abundant in RBC Important negative allosteric effector Bind to Hb in central cavity Stabilize T form by forming salt bridges
- 19. α1 α2 β1 β2 Eight cation groups Five anionic groups of BPG + The cleft is too narrow in HbO2 state.
- 21. Factors affecting 2,3-BPG concentration Increase Hormones – thyroid, GH, androgens Exercise Anemia Chronic hypoxia High altitude Decrease Acidosis (pH↓)
- 22. Without 2,3-BPG, the O2 saturation curve of Hb would approach to Mb
- 23. CONCLUSION Diffusion greatly limits the size of organisms. Circulatory systems overcome this. Hemoglobin are also required because O2 is only slightly soluble in blood. Allosteric effect allows the Hb to get efficient transport of oxygen.
- 24. THANKS