Heme B
{{chembox
| verifiedrevid = 396492132
| ImageFile = Heme B.svg
| ImageSize = 150px
| ImageAlt = Skeletal formula of heme B
| ImageFile1 = Haem-B-based-on-xtal-3D-sf.png
| ImageSize1 = 170
| ImageAlt1 = Space-filling model of the heme B complex
| IUPACName = Iron(II) 3-[18-(2-carboxyethyl)-8,13-bis(ethenyl)-3,7,12,17-tetramethylporphyrin-21,23-diid-2-yl]propanoic acid
| OtherNames = Iron protoporphyrin IX,
protoheme IX
| Section1 = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 16739950
| InChI = 1/C34H34N4O4.Fe/c1-7-21-17(3)25-13-26-19(5)23(9-11-33(39)40)31(37-26)16-32-24(10-12-34(41)42)20(6)28(38-32)15-30-22(8-2)18(4)27(36-30)14-29(21)35-25;/h7-8,13-16H,1-2,9-12H2,3-6H3,(H4,35,36,37,38,39,40,41,42);/q;+2/p-2/b25-13-,26-13-,27-14-,28-15-,29-14-,30-15-,31-16-,32-16-;/rC34H32FeN4O4/c1-7-21-17(3)25-13-29-20(6)24(10-12-34(42)43)32-16-28-23(9-11-33(40)41)18(4)26(37-28)14-31-22(8-2)19(5)30(15-27(21)36-25)38(31)35-39(29)32/h7-8,13-16H,1-2,9-12H2,3-6H3,(H,40,41)(H,42,43)/b25-13-,26-14-,27-15-,28-16-,29-13-,30-15-,31-14-,32-16-
| InChIKey = KABFMIBPWCXCRK-SMDPYJEOBB
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C34H34N4O4.Fe/c1-7-21-17(3)25-13-26-19(5)23(9-11-33(39)40)31(37-26)16-32-24(10-12-34(41)42)20(6)28(38-32)15-30-22(8-2)18(4)27(36-30)14-29(21)35-25;/h7-8,13-16H,1-2,9-12H2,3-6H3,(H4,35,36,37,38,39,40,41,42);/q;+2/p-2/b25-13-,26-13-,27-14-,28-15-,29-14-,30-15-,31-16-,32-16-;
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = KABFMIBPWCXCRK-RGGAHWMASA-L
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 14875-96-8
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 42VZT0U6YR
| PubChem = 444098
| SMILES = OC(=O)CC/C6=C(\C)/C=3/N=C6/C=C2/C(/CCC(O)=O)=C(/C)\C1=C\C5=N\C(=C/c4n([Fe]N12)c(C=3)c(C=C)c4C)C(\C=C)=C5\C
| MeSHName = Heme+b
| SMILES1 = OC(=O)CC/c6c(\C)c3n7c6cc2c(/CCC(O)=O)c(/C)c1cc5n8c(cc4n([Fe]78n12)c(c=3)c(C=C)c4c)c(\C=C)c5\C
}}
| Section2 = {{Chembox Properties
| Formula = C34H32O4N4Fe
| MolarMass = 616.487
| Appearance =
| Density =
| MeltingPt =
| BoilingPt =
}}
| Section3 = {{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt =
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}}
Heme B or haem B (also known as protoheme IX) is the most abundant heme.{{Citation |last=Ogun |first=Aminat S. |title=Biochemistry, Heme Synthesis |date=2022 |url=http://www.ncbi.nlm.nih.gov/books/NBK537329/ |work=StatPearls |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=30726014 |access-date=2023-01-03 |last2=Joy |first2=Neena V. |last3=Valentine |first3=Menogh}} Hemoglobin and myoglobin are examples of oxygen transport proteins that contain heme B. The peroxidase family of enzymes also contain heme B. The COX-1 and COX-2 enzymes (cyclooxygenase) of recent fame, also contain heme B at one of two active sites.
Generally, heme B is attached to the surrounding protein matrix (known as the apoprotein) through a single coordination bond between the heme iron and an amino-acid side-chain.
Both hemoglobin and myoglobin have a coordination bond to an evolutionarily-conserved histidine, while nitric oxide synthase and cytochrome P450 have a coordination bond to an evolutionarily-conserved cysteine bound to the iron center of heme B.
Since the iron in heme B containing proteins is bound to the four nitrogens of the porphyrin (forming a plane) and a single electron donating atom of the protein, the iron is often in a pentacoordinate state. When oxygen or the toxic carbon monoxide is bound the iron becomes hexacoordinated.
The correct structures of heme B and heme S were first elucidated by German chemist Hans Fischer.{{cite book | last1 = Fischer|first1=H. | last2 = Orth|first2=H. | title =Die Chemie des Pyrrols | location = Liepzig | publisher = Akademische Verlagsgesellschaft | date =1934 |title-link=Die Chemie des Pyrrols }}
{{Enzyme cofactors}}
{{tetrapyrroles}}