Editing Myoglobin (section)

==Structure and bonding==
Myoglobin belongs to the [[globin]] superfamily of proteins, and as with other globins, consists of eight [[alpha helices]] connected by loops.  Human myoglobin contains 154 amino acids.<ref name = "P02144">{{UniProt Full|P02144}}</ref>

Myoglobin contains a [[porphyrin]] ring with an iron at its center. A ''proximal'' [[histidine]] group (His-93) is attached directly to iron, and a ''distal'' histidine group (His-64) hovers near the opposite face.<ref name = "P02144"/>  The distal imidazole is not bonded to the iron, but is available to interact with the substrate O<sub>2</sub>.  This interaction encourages the binding of O<sub>2</sub>, but not carbon monoxide (CO), which still binds about 240× more strongly than O<sub>2</sub>.{{cn|date=June 2024}}

The binding of O<sub>2</sub> causes substantial structural change at the Fe center, which shrinks in radius and moves into the center of N4 pocket.  O<sub>2</sub>-binding induces "spin-pairing": the five-coordinate ferrous deoxy form is [[high spin]] and the six coordinate oxy form is low spin and [[diamagnetic]].{{Citation needed|reason=Reliable source needed for the whole sentence|date=March 2017}}

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File:MbO2MO.png|Molecular orbital description of Fe-O<sub>2</sub> interaction in myoglobin.<ref>{{cite journal | vauthors = Drago RS | title  = Free radical reactions of transition metal systems | journal = Coordination Chemistry Reviews | year = 1980 | volume = 32 | pages = 97–110 | doi = 10.1016/S0010-8545(00)80372-0 | issue = 2 }}</ref>
File:1a6m Oxy-Myoglobin.jpg|This is an image of an oxygenated myoglobin molecule. The image shows the structural change when oxygen is bound to the iron atom of the heme prosthetic group. The oxygen atoms are colored in green, the iron atom is colored in red, and the heme group is colored in blue.
File:Myoglobine.gif|Myoglobin
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