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Heme is a coordination complex "consisting of an iron ion coordinated to a tetrapyrrole acting as a tetradentate ligand, and to one or two axial ligands". [5] The definition is loose, and many depictions omit the axial ligands. [6]
(b) structure of the heme molecular component of hemoglobin. Normal human hemoglobins are tetrameric proteins composed of two pairs of globin chains, each of which contains one α (alpha) chain and one β (beta) chain. Each globin chain is associated with an iron-containing heme moiety. Throughout life, the synthesis of the α and the β chains ...
The name hemoglobin (or haemoglobin) is derived from the words heme (or haem) and globin, reflecting the fact that each subunit of hemoglobin is a globular protein with an embedded heme group. Each heme group contains one iron atom, that can bind one oxygen molecule through ion-induced dipole forces.
Occasionally, a moiety may contain smaller moieties and functional groups. [citation needed] A moiety that acts as a branch extending from the backbone of a hydrocarbon molecule is called a substituent or side chain, which typically can be removed from the molecule and substituted with others.
The mammalian enzyme contains one heme per dimer, with a proximal histidine ligand located in the HNOX domain of the beta 1 subunit. In its Fe(II) form, this heme moiety is the target of nitric oxide, which is synthesized by endothelial cells following appropriate stimulation. Binding of nitric oxide to the heme results in activation of the C ...
The globins are a superfamily of heme-containing globular proteins, involved in binding and/or transporting oxygen. These proteins all incorporate the globin fold, a series of eight alpha helical segments. Two prominent members include myoglobin and hemoglobin. Both of these proteins reversibly bind oxygen via a heme prosthetic group.
Biliverdin results from the breakdown of the heme moiety of hemoglobin in erythrocytes. Macrophages break down senescent erythrocytes and break the heme down into biliverdin along with hemosiderin, in which biliverdin normally rapidly reduces to free bilirubin. [1] [3] Biliverdin is seen briefly in some bruises as a green color.
The heme moiety consists of a porphyrin ring called Fe(II)-protoporphyrin IX (FP). To avoid destruction by this molecule, the parasite biocrystallizes heme to form hemozoin , a nontoxic molecule. Hemozoin collects in the digestive vacuole as insoluble crystals.