Chemical coordination complex of an iron ion chelated to a porphyrin
Binding of oxygen to a heme prosthetic group
Heme (American English), or haem (Commonwealth English, both pronounced /hi:m/ HEEM), is a ring-shaped iron-containing molecular component of hemoglobin, which is necessary to bind oxygen in the bloodstream. It is composed of four pyrrole rings with 2 vinyl and 2 propionic acid side chains.[1] Heme is biosynthesized in both the bone marrow and the liver.[2]
Heme plays a critical role in multiple different redox reactions in mammals, due to its ability to carry the oxygen moiety. Reactions include oxidative metabolism (cytochrome c oxidase, succinate dehydrogenase), xenobiotic detoxification via cytochrome P450 pathways (including metabolism of some drugs), gas sensing (guanyl cyclases, nitric oxide synthase), and microRNA processing (DGCR8).[3][4]
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] Among the metalloporphyrins deployed by metalloproteins as prosthetic groups, heme is one of the most widely used[7] and defines a family of proteins known as hemoproteins. Hemes are most commonly recognized as components of hemoglobin, the red pigment in blood, but are also found in a number of other biologically important hemoproteins such as myoglobin, cytochromes, catalases, heme peroxidase, and endothelial nitric oxide synthase.[8][9]
The word haem is derived from Greek αἷμαhaima 'blood'.
Space-filling model of the Fe-protoporphyrin IX subunit of heme B. Axial ligands omitted. Color scheme: grey=iron, blue=nitrogen, black=carbon, white=hydrogen, red=oxygen
^Hodgson E, Roe RM, Mailman RB, Chambers JE, eds. (2015). "H". Dictionary of Toxicology (3rd ed.). Academic Press. pp. 173–184. doi:10.1016/B978-0-12-420169-9.00008-4. ISBN 978-0-12-420169-9. Retrieved 2024-02-21.
^Bloomer JR (1998). "Liver metabolism of porphyrins and haem". Journal of Gastroenterology and Hepatology. 13 (3): 324–329. doi:10.1111/j.1440-1746.1998.01548.x. PMID 9570250. S2CID 25224821.
^Dutt S, Hamza I, Bartnikas TB (2022-08-22). "Molecular Mechanisms of Iron and Heme Metabolism". Annual Review of Nutrition. 42 (1): 311–335. doi:10.1146/annurev-nutr-062320-112625. ISSN 0199-9885. PMC 9398995. PMID 35508203.
^Ogun AS, Joy NV, Valentine M (2024), "Biochemistry, Heme Synthesis", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 30726014, retrieved 2024-02-22
^Chemistry IU (2009). "Hemes (heme derivatives)". IUPAC Compendium of Chemical Terminology. IUPAC. doi:10.1351/goldbook.H02773. ISBN 978-0-9678550-9-7. Archived from the original on 22 August 2017. Retrieved 28 April 2018.
^A standard biochemistry text defines heme as the "iron-porphyrin prosthetic group of heme proteins"(Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.)
^Poulos TL (2014-04-09). "Heme Enzyme Structure and Function". Chemical Reviews. 114 (7): 3919–3962. doi:10.1021/cr400415k. ISSN 0009-2665. PMC 3981943. PMID 24400737.
^Paoli M (2002). "Structure-function relationships in heme-proteins" (PDF). DNA Cell Biol. 21 (4): 271–280. doi:10.1089/104454902753759690. hdl:20.500.11820/67200894-eb9f-47a2-9542-02877d41fdd7. PMID 12042067. S2CID 12806393. Archived (PDF) from the original on 2018-07-24.
^Alderton W (2001). "Nitric oxide synthases: structure, function and inhibition". Biochem. J. 357 (3): 593–615. doi:10.1042/bj3570593. PMC 1221991. PMID 11463332.
Heme (American English), or haem (Commonwealth English, both pronounced /hi:m/ HEEM), is a ring-shaped iron-containing molecular component of hemoglobin...
(about 20–25% of the total) as carbaminohemoglobin, in which CO2 binds to the heme protein. The molecule also carries the important regulatory molecule nitric...
Heme arginate (or haem arginate) is a compound of heme and arginine used in the treatment of acute porphyrias. This heme product is only available outside...
Heme oxygenase, or haem oxygenase, (HMOX, commonly abbreviated as HO) is an enzyme that catalyzes the degradation of heme to produce biliverdin, ferrous...
Heme A (or haem A) is a heme, a coordination complex consisting of a macrocyclic ligand called a porphyrin, chelating an iron atom. Heme A is a biomolecule...
Heme B or haem B (also known as protoheme IX) is the most abundant heme. Hemoglobin and myoglobin are examples of oxygen transport proteins that contain...
Heme C (or haem C) is an important kind of heme. The correct structure of heme C was published in mid 20th century by the Swedish biochemist K.-G. Paul...
mechanism results in a decrease in the amount of heme produced and a build-up of substances involved in making heme. Porphyrias may also be classified by whether...
haemoprotein), or heme protein, is a protein that contains a heme prosthetic group. They are a very large class of metalloproteins. The heme group confers...
Heme O (or haem O) differs from the closely related heme A by having a methyl group at ring position 8 instead of the formyl group. The isoprenoid chain...
Cytochromes are redox-active proteins containing a heme, with a central iron (Fe) atom at its core, as a cofactor. They are involved in the electron transport...
a sign indicating the presence of underlying diseases involving abnormal heme metabolism, liver dysfunction, or biliary-tract obstruction. The prevalence...
red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance...
experimental success in vitro. Heme, an important prosthetic group present in Complexes I, II, and IV can also be targeted, since heme biosynthesis and uptake...
HMOX1 (heme oxygenase 1 gene) is a human gene that encodes for the enzyme heme oxygenase 1 (EC 1.14.99.3). Heme oxygenase (abbreviated HMOX or HO) mediates...
A heme transporter is a protein that delivers heme to the various parts of a biological cell that require it. Heme is a major source of dietary iron in...
Metabolic intermediates are molecules that are the precursors or metabolites of biologically significant molecules. Although these intermediates are of...
Heme ligase (EC 4.99.1.8, heme detoxification protein, HDP, hemozoin synthase) is an enzyme with systematic name Fe3+:ferriprotoporphyrin IX ligase (β-hematin-forming)...
(haemin; ferric chloride heme) is an iron-containing porphyrin with chlorine that can be formed from a heme group, such as heme B found in the hemoglobin...
porphyria (AIP) is a rare metabolic disorder affecting the production of heme resulting from a deficiency of the enzyme porphobilinogen deaminase. It is...
two alpha subunits and two beta subunits (α2β2). Each subunit contains a heme group that diatomic oxygen (O2) molecules can bind to. In addition to oxygen...
consists of non-polar amino acids at the core of the globulin, where the heme group is non-covalently bounded with the surrounding polypeptide of myoglobin...
that binds heme. This motif is located towards the N-terminus of the peptide chain and contains a histidine as the 5th ligand of the heme iron. The 6th...
food that contains enough iron, which could be found in both heme and non-heme iron. Heme iron: Red meat (for example, beef, pork, lamb, goat, or venison)...
SDHC and SDHD remains unclear. Especially in case of heme b insertion and even its function. Heme b prosthetic group does not appear to be part of electron...
role in living organisms as a precursor to other critical compounds like heme (hemoglobin) and chlorophyll. It is a deeply colored solid that is not soluble...
bridges (=CH−). In vertebrates, an essential member of the porphyrin group is heme, which is a component of hemoproteins, whose functions include carrying oxygen...
chromoproteins. Hemoglobin contains the prosthetic group known as heme. Each heme group contains an iron ion (Fe2+) which forms a co-ordinate bond with...
of heme catabolism. It is the pigment responsible for a greenish color sometimes seen in bruises. Biliverdin results from the breakdown of the heme moiety...
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