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14 - Wednesday October 14th 2009 Biochemistry 405 Lecture#7...

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1 Wednesday, October 14 th, 2009 Biochemistry 405 Lecture #7 Kane Hall 130 10:30- 11:20 am Lecturer: Wim Hol Slide Set #1
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2 Myoglobin, Hemoglobin and Oxygen transport Outline - Structure of Myoglobin (Mb) and O 2 binding to Mb. - Structure of Hemoglobin (Hb) & O 2 binding to Hb. - Bohr Effect coupling of O 2 binding and H + release. - Models of cooperativity. - Role of 2,3-BPG at high altitudes. - Detour to blue blood. - Sickle cell hemoglobin and malaria.
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3 Myoglobin Waiting in muscle cells for oxygen to arrive Heme group in red with spherical Fe(II) ion in center. Helices are labeled A to H. Helix-connecting loops are AB, BC, etc
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4 Oxy-myoglobin s heme group with Fe(II) binding oxygen Histidine F8 interacts with the Fe(II), as do four nitrogens of the heme group. In Oxy-Mb one oxygen atom of O 2 also binds to the Fe(II). The Fe(II) in oxy-Mb is octahedrally coordinated by six ligands. His F8 In hemoglobin and myoglobin residue F8 means: the 8th amino acid in helix F.
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Myoglobin the Heme complex The heme group is packed in between hydrophobic side chains including: ValE11 and PheCD1. When O 2 is bound it also interacts with N İ 2 of the imidazole of HisE7. The oxygen binding pocket is quite tight (several additional residues are not shown for clarity).
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Oxygen Binding Curve of Myoglobin General: The Fractional saturation of a protein by ligand, L, is the fraction of binding sites occupied by L relative to the total available sites. Specific: The Fractional oxygen saturation Y O2 , is the fraction of O 2 -binding sites occupied by O 2. pO 2 is the partial pressure of O 2 . (pO 2 in venous blood is ~ 30 torr (760 torr = 760 mm Hg = 1 atmosphere) ) Mb + O 2 MbO 2 The dissociation constant K: K = [O 2 ][Mb]/[MbO 2 ] since the definition of Y is: Y = [MbO 2 ]/([MbO 2 ] + [Mb]) After a lot of rearrangements, this yields: Y = pO 2 /(pO 2 + K) When Y = 0.5 then: K = P 50 The shape of the curve is hyperbolic
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Hemoglobin (Hb) is much more sophisticated than myoglobin: 1. Hb has four myoglobin-like subunits. 2. As a result of cross-talk between these four subunits the oxygen binding curve of Hb is NOT hyperbolic but S-shaped. This is called cooperativity . This increases the efficiency of oxygen transport from lung to other organs. 3. Its oxygen-affinity is pH-dependent . 4. Its oxygen-affinity can be regulated allosterically by BPG. Hemoglobin The oxygen transporter in the blood of most animals It is usually embedded in red blood cells .
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Deoxy Hemoglobin View along the two-fold. Notice the real significant differences with the next slide.
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View along the two-fold. Notice the real significant differences with the previous slide. OxyHemoglobin
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Deoxy-Hb T-state Shift in structure in the T -> R transition involves both tertiary and quaternary structure changes.
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