Heme B

Heme B or haem B (also known as protoheme IX) is the most abundant heme.^[1] 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.

Heme B

Names
IUPAC name Iron(II) 3-[18-(2-carboxyethyl)-8,13-bis(ethenyl)-3,7,12,17-tetramethylporphyrin-21,23-diid-2-yl]propanoic acid
Other names Iron protoporphyrin IX, protoheme IX
Identifiers
CAS Number	14875-96-8 Y
3D model (JSmol)	Interactive image Interactive image
ChemSpider	16739950 Y
ECHA InfoCard	100.114.904
MeSH	Heme+b
PubChem CID	444098
UNII	42VZT0U6YR Y
CompTox Dashboard (EPA)	DTXSID90889386
InChI InChI=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-; Y Key: KABFMIBPWCXCRK-RGGAHWMASA-L Y 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- Key: KABFMIBPWCXCRK-SMDPYJEOBB
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 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
Properties
Chemical formula	C34H32O4N4Fe
Molar mass	616.487
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

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.^[2]