User:Michael Roberts/BIOL115 Myo: Difference between revisions

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'''PROXIMAL AND DISTAL HISTIDINES''': The iron atom sits either side of the side chains of two <scene name='User:Michael_Roberts/BIOL115_Myo/Heme/4'>histidine residues</scene>.

One of these (coloured cyan) is attached to the iron atom, and is known as the ''proximal'' histidine. It is also referred to as His F8, because it is the eighth residue of helix F. The other (green) is called the ''distal'' histidine, also referred to as ~~his~~ E7 (~~7th~~ residue of helix E).

One of these (coloured cyan) is attached to the iron atom, and is known as the ''proximal'' histidine. It is also referred to as His F8, because it is the eighth residue of helix F. The other (green) is called the ''distal'' histidine, also referred to as His E7 (7th residue of helix E).

Note how the iron is pulled out slightly to one side of the plane of the ~~heam~~ group as a result of it's co-ordination with the side chain of the proximal histidine.

Note how the iron is pulled out slightly to one side of the plane of the haem group as a result of it's co-ordination with the side chain of the proximal histidine.

'''OXYGEN''':

The space between the iron and the distal histidine is where the <scene name='User:Michael_Roberts/BIOL115_Myo/Heme/6'>oxygen</scene> (pink) binds.

Note the angled orientation of the oxygen relative to the plane of the ~~heam~~. The ~~natural binding of~~ oxygen ~~to heam in solution would be~~ the ~~O2 molecule perpendicular to~~ the ~~plane. In myoglobin (and haemoglobin) the presence~~ of the distal His ~~forces to O2 to one side~~, ~~reducing~~ the ~~affinity of the heam-~~O2 ~~binding, thus allowing release of oxygen when pO2 is low~~. The ~~same effect~~ of the distal His also reduces the affinity of ~~heam~~ for carbon monoxide.

Note the angled orientation of the oxygen relative to the plane of the haem. The oxygen-haem complex is stabilised by the presence of the side chain of the distal His, which contributes a hydrogen atom that hydrogen bonds with the O2. The presence of the distal His also reduces the affinity of haem for carbon monoxide, by displacing it from it's more natural position perpendicular to the plane of the haem into a more angled position, similar to bound O2.

</StructureSection>

@@ Line 41: / Line 41: @@
 '''PROXIMAL AND DISTAL HISTIDINES''': The iron atom sits either side of the side chains of two <scene name='User:Michael_Roberts/BIOL115_Myo/Heme/4'>histidine residues</scene>.
-One of these (coloured cyan) is attached to the iron atom, and is known as the ''proximal'' histidine. It is also referred to as His F8, because it is the eighth residue of helix F. The other (green) is called the ''distal'' histidine, also referred to as his E7 (7th residue of helix E).
+One of these (coloured cyan) is attached to the iron atom, and is known as the ''proximal'' histidine. It is also referred to as His F8, because it is the eighth residue of helix F. The other (green) is called the ''distal'' histidine, also referred to as His E7 (7<sup>th</sup> residue of helix E).
-Note how the iron is pulled out slightly to one side of the plane of the heam group as a result of it's co-ordination with the side chain of the proximal histidine.
+Note how the iron is pulled out slightly to one side of the plane of the haem group as a result of it's co-ordination with the side chain of the proximal histidine.
 '''OXYGEN''':
 The space between the iron and the distal histidine is where the <scene name='User:Michael_Roberts/BIOL115_Myo/Heme/6'>oxygen</scene> (pink) binds.
-Note the angled orientation of the oxygen relative to the plane of the heam. The natural binding of oxygen to heam in solution would be the O<sub>2</sub> molecule perpendicular to the plane. In myoglobin (and haemoglobin) the presence of the distal His forces to O<sub>2</sub> to one side, reducing the affinity of the heam-O<sub>2</sub> binding, thus allowing release of oxygen when pO<sub>2</sub> is low. The same effect of the distal His also reduces the affinity of heam for carbon monoxide.
+Note the angled orientation of the oxygen relative to the plane of the haem. The oxygen-haem complex is stabilised by the presence of the side chain of the distal His, which contributes a hydrogen atom that hydrogen bonds with the O<sub>2</sub>. The presence of the distal His also reduces the affinity of haem for carbon monoxide, by displacing it from it's more natural position perpendicular to the plane of the haem into a more angled position, similar to bound O<sub>2</sub>.
 </StructureSection>

User:Michael Roberts/BIOL115 Myo: Difference between revisions

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