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Myoglobin
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- 1JOb of myoglobin in humansmyoglobin facilitates the diffusion of oxygen, into the mitochondria
- 2HistoryFirst Protein Structure
Myoglobin was purified from whale blood by Max Perutz in 1958.
Showed a 75% a-helical fold.
- 155 amino acids, ~ Mr: 17000 - 3Key featuresAbout 75% of the main chain is folded into RH - helices, referred to as A-H,
Helical segments are generally terminated by Proline residues, a cyclic residue with a locked conformational angle. - 4Structure of MbThe interior - made of nearly fully non-polar residues.
The crevice - haem group present surrounded by non-polar residues - 5Problems of O2 binding to haemO2 has only limited solubility (1 X 10-4 M) in water.
O2 will diffuse only very slowly in tissues.
Binding of O2 to a free heme group is irreversible. - 6The solutionEnclosure the heme group in a protein to allow reversible binding and overcome the solubility problem and this acts as the transporter.
- 7The haem (Fe2+) group- Confers O2 binding on Mb and Hb
- Give the colour
- Consists of Fe2+ & protoporphyin IX
- The Fe2+ binds to 4N's and has 5th & 6th coordinations - 8The 2 key HistidinesProximal F8 His
Distal E7 His - 9Proximal F8- directly bonded to haem
- Occupies 5th coordination position
- The Fe2+ is 0.3A out of the plane of porphyrin - 10Distal E7- Not directly bonded to haem
- Occupies 6th coordination position
- reduces the affinity of binding carbon monoxide for the site
- sterically blocks the formation of myoglobin associates - 11CO Bindng- CO binds tightly; linear.
- O2 binds less tightly, bent structure.
- Distal His forces bent binding of both, weakens CO binding. - 12unloading O2 is keyMb + O2 === MbO2
- 13Mb - O2 (p50 from graph)- A hyperbolic curve
- The p50 = 2.75 mm Hg is the partial pressure at which 50% of myoglobin molecules have released their O2.
- Mb has low affinity in mt and high in venous blood - 14SummaryMyoglobin inside muscle cells facilitates the diffusion of oxygen by binding oxygen when O2 concentration is high (at the interface with the extracellular fluid) and releasing it where O2 concentration is low (at the mitochondria).
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- Descripción
- BIOL 115: Protein biochemistry Fichas sobre Myoglobin, creado por Jumael Zafar el 26/03/2019.
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- Jumael Zafar
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