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16 - Lecture 16 Cooperativity and the mechanism of oxygen...

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Lecture 16: Cooperativity and the mechanism of oxygen uptake by hemoglobin Monday, August 23, 2010
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How can we rationalize the structure of hemoglobin with its oxygen binding characteristics? The unbound and bound states of hemoglobin have slightly di ff erent structures. The unbound form (referred to as the T, or tense, state): Monday, August 23, 2010
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The bound form, referred to as the R (or relaxed) form The relaxed form has a signi fi cantly higher a nity for oxygen than the tense form. Monday, August 23, 2010
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But, the tense form is the more stable version of hemoglobin: it is stabilized by a series of electrostatic interactions between the subunits: Monday, August 23, 2010
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Thus, when oxygen is not bound, hemoglobin adopts the more stable T state, with its own low a nity oxygen binding curve Monday, August 23, 2010
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Oxygen binding to the heme group induces a small change in the conformation of the subunit to which it is bound Monday, August 23, 2010
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Monday, August 23, 2010
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This change in the planarity of the heme plate gets transferred to an adjacent alpha helix Monday, August 23, 2010
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Monday, August 23, 2010
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This subtle shift in helix F causes electrostatic interactions between the subunits to be broken, and a new set to be formed Monday, August 23, 2010
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This rotates the subunits with respect to one another, causing the shift from the T to R state: Monday, August 23, 2010
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