12 22 Sept 2010

12 22 Sept 2010 - α 2 β 2 Hemoglobin tetramer α 1 β 1 α 2 β 2 α 1 α 2 β 1 β 2 A B G G B A A B G G B A C FG C FG C FG C FG switch hinge

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Unformatted text preview: α 2 β 2 Hemoglobin tetramer ( α 1 β 1 )( α 2 β 2 ) α 1 α 2 β 1 β 2 A B G G B A A B G G B A C FG C FG C FG C FG switch hinge switch hinge • The low and high affinity states follow hyperbolic binding • Oxygen titrations involve stepwise increases of oxygen partial pressure • At low pO2, the T-state low affinity curve is followed • As pO2 increases, the Hb shifts to R-state high affinity • The resultant curve is sigmoidal • Sigmoidal curves are indicative of cooperativity – one subunit influencing the affinity of another subunit through conformational changes • The binding curve for myoglobin is hyperbolic • The binding curve for hemoglobin is sigmodial • Higher affinity in the presence of higher oxygen concentrations • Lower affinity at lower oxygen concentrations • The carrier activity of Mb and Hb are coupled • Myoglobin acts as a reservoir to maintain oxygen levels • When activity is high, Mb can extract oxygen from Hb • CO and O2 have similar k a (k on ) but CO has slower kd (k off ) therefore K d is much lower = higher affinity • Most people have about 1 – 3 % of Hb sites occupied by carbon monoxide, smokers up to 15% • Ligand binding increases affinity, CO locks Hb into the high affinity state • The switch to T-state is blocked and O 2 release is limited Nomenclature • Cooperativity – Changes in one subunit influence properties of adjacent subunits- Cooperativity can be either positive or negative • Allosteric – “other” binding sites which modulate activity...
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This note was uploaded on 09/18/2011 for the course CHEM 3510 taught by Professor Mueser during the Spring '10 term at Toledo.

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12 22 Sept 2010 - α 2 β 2 Hemoglobin tetramer α 1 β 1 α 2 β 2 α 1 α 2 β 1 β 2 A B G G B A A B G G B A C FG C FG C FG C FG switch hinge

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