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myoglobin
- 1. MYOGLOBIN Dr.PRABHJOT KAUR BHINDER DEPTT OF BIOCHEMISTRY 9/1/2017 1
- 2. Structure of myoglobin Andrew Kendrew and Max Perutz solved the structure of myoglobin in 1959 to 1968. Myoglobin was the first protein whose structure was determined by X- ray crystallography Myoglobin: 44 x 44 x 25 Å single subunit 153 amino acid residues 121 residues are in an a helix. Helices are named A, B, C, …F. The heme pocket is surrounded by E and F but not B, C, G, also H is near the heme. Amino acids are identified by the helix and position in the helix or by the absolute numbering of the residue.
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- 6. Structure of HemoglobinStructure of Hemoglobin
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- 10. MyoglobinMyoglobin HemeHeme 2 α chains 2 β chains HemoglobinHemoglobin
- 11. The Heme group •Each subunit of hemoglobin or myoglobin contains a heme. •Binds one molecule of oxygen •Protoporphyrin 9 The iron must be in the Fe(II) form or reduced form. (ferrous oxidation) state.
- 12. The Conformation Change The secret of Mb Oxygen binding changes the Mb conformation Without oxygen bound, Fe is out of heme plane Oxygen binding pulls the Fe into the heme plane Fe pulls its His F8 ligand along with it The F helix moves when oxygen binds Total movement of Fe is 0.029 nm - 0.29 A
- 14. Function of the globin Protoporphyrin binds oxygen to the sixth ligand of Fe(II) out of the plane of the heme. The fifth ligand is a Histidine, F8 on the side across the heme plane. His F8 binds to the proximal side and the oxygen binds to the distal side. The heme alone interacts with oxygen such that the Fe(II) becomes oxidized to Fe(III) and no longer
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- 16. MyoglobinMyoglobin oxygen storage protein of skeletal muscles. As with the cytochrome example, both proteins use heme groups. It acts as the binding site for molecular oxygen.
- 18. Myoglobin facilitates rapidly respiring muscle tissue The rate of O2 diffusion from capillaries to tissue is slow because of the solubility of oxygen. Myoglobin increases the solubility of oxygen. Myoglobin facilitates oxygen diffusion. Oxygen storage is also a function because Myoglobin concentrations are 10-fold greater in whales and seals than in land mammals
- 19. Myoglobin follows the michaelis- menten graph It follow michaelis-menton because it is a simple chemical equilibrium 19
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- 24. Myoglobin Structure Mb is a monomeric heme protein Mb polypeptide "cradles" the heme group Fe in Mb is Fe2+ - ferrous iron - the form that binds oxygen Oxidation of Fe yields 3+ charge - ferric iron -metmyoglobin does not bind oxygen Oxygen binds as the sixth ligand to Fe
- 25. Myoglobin an iron containing protein in muscles ,receive oxygen from rbc and transports it to the mitochondria of muscle cells,where oxygen is used in cellular respiration to produce energy Oxymyoglobin –oxygen supply and act as scavenger of NO[MYOCYTES] Oxymyoglobin +NO= Harmless nitrates with ferric myoglobin ,which is recycled by metmyoglobin reductase 25
- 28. O2 binding to myoglobin 22 MbOOMb ↔+ ][MbO ][Mb][O Kd 2 2 = ][OKd ][O ][MbO[Mb] ][MbO Y 2 2 2 2 O2 + = + = Written backwards we can get the dissociation constant Fractional Saturation solve for [MbO2] and plug in
- 29. How do you measure the concentration of oxygen? Use the partial pressure of O2 or O2 tension = pO2 2d 2 O pOK pO Y 2 + = P50 = the partial oxygen pressure when YO2 = 0.50 250 2 O pOP pO Y 2 + =
- 30. P50 value for myoglobin is 2.8 torr or 1 torr = 1 mm Hg = 0.133 kPa 760 torr = 1 atm of pressure Mb gives up little O2 over normal physiological range of oxygen concentrations in the tissue i.e. 100 torr in arterial blood 30 torr in venous blood YO2 = 0.97 to YO2 = 0.91
- 32. Contrast Mb O2 binding to Hemoglobin YO2 = 0.95 at 100 torr but 0.55 at 30 torr a ∆YO2 of 0.40 Hb gives up O2 easier than Mb and the binding is Cooperative!!
- 33. Diseases Acute renal failure Heart attack Myoglobinuria [rhabdomyolysis] 33
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- 35. Causes of MYOGLOBINURIA Mc Ardles disease Phosphofructokinase deficiency Carnitine palmitoyltransferase 2 Malignant hyperthermia Polymyositis Lactate dehydrogenase deficiency Thermal or electric burns 35
- 36. Diagnosis After centrifuging ,urine of myoglobinuria is clear Serum of myoglobinuria changes from pink to red 36
- 37. Treatment Hospitalization and IV hydration Mannitol Sodium bicarbonates 37
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