LEC 16th - LEC 16th Quick review: Key features of...

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LEC 16 th Quick review: Key features of hemoglobin cooperativity to the Bohr effect and effect of 2,3 dpg allosteric modulator. Salt bridges that stabilize the hemoglobin in the low affinity quaternary confirmation (2,3 dpg fits in low affinity) we call it the T state. The salt bridges details ----4 alpha alpha bridges, 2 alpha beta, 2 internal beta-beta. Role of Tyrosine in FG corners, stabilizing salt bridges in T state. Binding of Oxygen— sequential breaking of salt bridges. Most of the salt bridge breakages are tertiary driven (oxygen binds to chain, breaks salt bridges associated with chain)--- this idea of induced tertiary changes is KNF like. Think of 2 models of cooperativity and how they apply. Addition or removal of 2,3 DPG is associated with quaternary conformational change and there is set of salt bridges that are quaternary linked, no change of number of oxygen but less salt bridges, the high affinity R confirmation. Notice, each of the polypeptide chains participates in the salt bridge involving amino acid side chain that undergoes pK change. Each subunit has associated bohr proton. In case of beta chains, Bohr proton is associated with immidozole of C terminal Histidine. Proton comes off as oxygen bound. It looks like 1:1 relationship between oxygen and proton comes off. To be precise 7/10 th of proton to oxygen. Whats important that there is linear relationship between proton binding and oxygen release and vice versa (KNF like). The last oxygen is associated with breakage of only beta-beta salt bridges. So the original fully deoxyganed proteins has 8 salt bridges, hard to get oxygen on. Constrained molecule. The last oxygen only has single salt bridge, easy to put last oxygen on. Another way to describe s shaped oxygen binding curve. Easier to put successive molecules KNF model—individual subunits bind oxygen, binding results in induced conformational changes confined to subunits that bound oxygen. Free energy of cooperativity arises from Intersubunit contacts are altered by the subunit specific conformational changes and free energy of cooperativity comes from
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This note was uploaded on 01/30/2010 for the course BIO 351 taught by Professor Hoffmann,j during the Fall '08 term at SUNY Stony Brook.

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LEC 16th - LEC 16th Quick review: Key features of...

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