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Heme B

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Heme B
Skeletal formula of heme B
Space-filling model of the heme B complex
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
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.114.904 Edit this at Wikidata
MeSH Heme+b
UNII
  • 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-; checkY
    Key: KABFMIBPWCXCRK-RGGAHWMASA-L checkY
  • 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
  • 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
C34H32O4N4Fe
Molar mass 616.487
Appearance Burgundy like solid #64293D (100,41,61)
Solubility Slightly soluble in ammonia water and pyridine
Related compounds
Related compounds
 Hemin, Hematin
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

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. Isolated heme B is slightly soluble in ammonia water and is extremely sensitive to oxygen, instantly oxidizing to a dark green to black-brown color when exposed to air.

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]

Chemical properties

[edit]
(Precipitated)
(Suspended)
These are four concentrated ammonia water solutions. From left to right: nicotinamide adduct of Heme B, carbon monoxide adduct of Heme B, nicotinic acid adduct of Heme B, and Heme B. They are slightly soluble in water and are all highly sensitive to oxygen in the air, requiring oxygen-free storage.

Heme B can be prepared by reducing Hemin in pyridine with sodium dithionite. Upon addition of the dithionite, the solution changed color and gelled: [3]

Reduction of Hemin with sodium dithionite
Reduction of Hemin with sodium dithionite

It can also be prepared by reducing Hemin with Raney nickel in ammonia water:

Reduction of Hemin with raney nickel
Reduction of Hemin with raney nickel

Degradation

[edit]
Main article: Heme § Degradation

In humans, heme B is degraded by the enzyme heme oxygenase to give biliverdin, which is then converted to bilirubin by biliverdin reductase.[4]

heme B
 
 
 
Rightward reaction arrow
 
 
 
2D representation of the chemical structure of biliverdin.
biliverdin
 
 
 
Rightward reaction arrow
 
 
 
2D representation of the chemical structure of bilirubin.
bilirubin

Bilirubin is either rendered water soluble by forming bilirubin diglucuronide and excreted from the liver in bile,[5] or further reduced to urobilinogen.[4][6]


References

[edit]
  1. ^ Ogun, Aminat S.; Joy, Neena V.; Valentine, Menogh (2022), "Biochemistry, Heme Synthesis", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 30726014, retrieved 2023-01-03
  2. ^ Fischer, H.; Orth, H. (1934). Die Chemie des Pyrrols. Leipzig: Akademische Verlagsgesellschaft.
  3. ^ Epstein, Lawrence M.; Straub, Darel K.; Maricondi, C. (1967). "Moessbauer spectra of some porphyrin complexes with pyridine, piperidine, and imidazole". Inorganic Chemistry. 6 (9): 1720–1724. doi:10.1021/ic50055a024.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ a b Watson, Cecil J. (1977). "Historical Review of Bilirubin Chemistry". In Berk, Paul D. (ed.). International Symposium on Chemistry and Physiology of Bile Pigments. U.S. Department of Health, Education, and Welfare, Public Health Service, National Institutes of Health. pp. 3–16.
  5. ^ King, C.; Rios, G.; Green, M.; Tephly, T. (2000). "UDP-Glucuronosyltransferases". Current Drug Metabolism. 1 (2): 143–161. doi:10.2174/1389200003339171. PMID 11465080.
  6. ^ Hall, Brantley; Levy, Sophia; Dufault-Thompson, Keith; Arp, Gabriela; Zhong, Aoshu; Ndjite, Glory Minabou; Weiss, Ashley; Braccia, Domenick; Jenkins, Conor; Grant, Maggie R.; Abeysinghe, Stephenie; Yang, Yiyan; Jermain, Madison D.; Wu, Chih Hao; Ma, Bing (2024-01-03). "BilR is a gut microbial enzyme that reduces bilirubin to urobilinogen". Nature Microbiology. 9 (1): 173–184. doi:10.1038/s41564-023-01549-x. ISSN 2058-5276. PMC 10769871. PMID 38172624.