Ann Taylor/Hemoglobin: Difference between revisions
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==T to R transition== | ==T to R transition== | ||
For hemoglobin to function as an oxygen-carrier in the blood, it must have an equilibrium between the two main states of its quaternary structure, the unliganded "deoxy" or "T state" versus the liganded "oxy" or "R state". The unliganded (deoxy) form is called the "T" (for "tense") state because it contains extra stabilizing interactions between the subunits, specifically <scene name='57/576710/Deoxy_salt_bridges/ | For hemoglobin to function as an oxygen-carrier in the blood, it must have an equilibrium between the two main states of its quaternary structure, the unliganded "deoxy" or "T state" versus the liganded "oxy" or "R state". The unliganded (deoxy) form is called the "T" (for "tense") state because it contains extra stabilizing interactions between the subunits, specifically <scene name='57/576710/Deoxy_salt_bridges/3'>ionic interactions</scene>. In the high oxygen affinity R-state conformation, these ionic interactions <scene name='57/576710/Oxy_ionic_interactions/1'>are lost</scene>, and the tetramer is described as "relaxed". In some organisms this difference is so pronounced that their Hb molecules dissociate into dimers in the oxygenated form. Structural changes that occur during this transition can illuminate how such changes result in important functional properties, such as cooperativity of oxygen binding and allosteric control by pH and anions. | ||
The Bohr effect is the increased stability of the T state due to protonation of histidine residues, especially <scene name='57/576710/Bohr_effect/2'>His 146</scene> of the beta chains. This is the C terminal residue of the beta chain. In the T state, the C terminal carboxylate group interacts with the positively charged side chain of lysine 40 of an alpha chain. When His 146 is protonated, it can also form an ionic interaction with Asp 94. This second interaction is one of several interactions which stabilizes the T state at lower pH. | The Bohr effect is the increased stability of the T state due to protonation of histidine residues, especially <scene name='57/576710/Bohr_effect/2'>His 146</scene> of the beta chains. This is the C terminal residue of the beta chain. In the T state, the C terminal carboxylate group interacts with the positively charged side chain of lysine 40 of an alpha chain. When His 146 is protonated, it can also form an ionic interaction with Asp 94. This second interaction is one of several interactions which stabilizes the T state at lower pH. | ||