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	{{Context|date=November 2009}}
	{{chembox		{{chembox
			| Verifiedfields = changed
⚫	| verifiedrevid = 404478338
			| Watchedfields = changed
		⚫	| verifiedrevid = 442000463
	| ImageFile = Heme c.svg		| ImageFile = Heme c.svg
	| ImageSize = 250px		| ImageSize = 250px
	| IUPACName =		| IUPACName =
	| OtherNames =		| OtherNames =
	| Section1 = {{Chembox Identifiers		|Section1={{Chembox Identifiers
			| CASNo_Ref = {{cascite|correct|??}}
	| CASNo = 26598-29-8
	| PubChem = 444125		| CASNo = 26598-29-8
	| SMILES =		| PubChem = 11987638
			| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
⚫	| MeSHName = heme+C
			| ChemSpiderID = 10160119
			| SMILES = OC(=O)CC/c6c(\C)c3n7c6cc2c(/CCC(O)=O)c(/C)c1cc5n8c(cc4n(78n12)c(c=3)c(C(S)=C)c4c)c(\C(S)=C)c5\C
			| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
			| StdInChI = 1S/C34H34N4O4S2.Fe/c1-15-21(7-9-31(39)40)27-14-28-22(8-10-32(41)42)16(2)24(36-28)12-29-34(20(6)44)18(4)26(38-29)13-30-33(19(5)43)17(3)25(37-30)11-23(15)35-27;/h11-14H,5-10H2,1-4H3,(H6,35,36,37,38,39,40,41,42,43,44);/q;+2/p-2/b23-11-,24-12-,25-11-,26-13-,27-14-,28-14-,29-12-,30-13-;
			| StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
			| StdInChIKey = KWLVFEFHZOXGTI-IDTMDVKXSA-L
		⚫	| MeSHName = heme+C
	}}		}}
	| Section2 = {{Chembox Properties		|Section2={{Chembox Properties
	| Formula = C<sub>34</sub>H<sub>36</sub>O<sub>4</sub>N<sub>4</sub>S<sub>2</sub>Fe		| Formula = C<sub>34</sub>H<sub>36</sub>O<sub>4</sub>N<sub>4</sub>S<sub>2</sub>Fe
	| MolarMass = 684.651 g/mol		| MolarMass = 684.64904 g/mol
	| Appearance =		| Appearance =
	| Density =		| Density =
	| MeltingPt =		| MeltingPt =
	| BoilingPt =		| BoilingPt =
	}}		}}
	| Section3 = {{Chembox Hazards		|Section3={{Chembox Hazards
	| Solubility =		| MainHazards =
	| MainHazards =		| FlashPt =
	| FlashPt =		| AutoignitionPt =
	| Autoignition =
	}}		}}
	}}		}}
			'''Heme C''' (or '''haem C''') is an important kind of ].
⚫	'''Heme C''' (or '''haem C''') differs from ] in that the two ] side chains of heme B are replaced by covalent, ] linkages to the ]. These linkages do not allow the heme C to easily dissociate from the ], ], compared with the more easily dissociated heme B that may dissociate from the holoprotein, the heme-protein complex, even under mild conditions. This allows a very wide range of cytochrome c structure and function, with the myriad of c type ] acting primarily as electron carriers. Cytochromes c, existing as dozens to hundreds of structural and functional subtypes, are found in a wide variety of cell types, even in those organisms living under extreme conditions. While heme B plays a variety of roles in cells, heme C is almost always located in proteins functioning in ] reactions most often associated with cell, ] or ] membranes. Heme C, along with the closely structurally related Heme B, are the most common heme types observed in functioning ].
			==History==
	The thioether linkages are commonly arranged with two amino acids between the two cysteinyl groups bound to the heme. This is often written as CXXC, within the amino acid sequence presentation with X being most any common amino acid. Vertebrate c type cytochromes also arrange a ] amino acid next to this sequence so that CXXCH represents the five key amino acids associated with the thioether linkages in these proteins. The two thioether bonds are made to heme ring positions 2 and 4, but a few c type cytochromes have hemes with only a single thioether bond.<ref>{{cite journal | doi=10.1098/rstb.2002.1192 | author=Allen, J.W.A., Daltrop, O., Stevens, J.M., Ferguson, S.J.| title=C-type cytochromes: diverse structures and biogenisis systems pose evolutionary problems| journal=Phil. Trans. R. Soc. Lond. B| year=2003 | volume=358 | pages= 255–266 }}</ref>
		⚫	The correct structure of heme C was published in mid 20th century by the Swedish biochemist K.-G. Paul.<ref>{{cite journal | doi=10.3891/acta.chem.scand.04-0239 | author=Paul, K.G. | last2=Högfeldt | first2=Erik | last3=Sillén | first3=Lars Gunnar | last4=Kinell | first4=Per-Olof| title=The splitting with silver salts of the cysteine-porphyrin bonds in cytochrome c | journal=Acta Chemica Scandinavica| year=1950 | volume=4 | pages= 239–244| doi-access=free }}</ref> This work confirmed the structure first inferred by the great Swedish biochemist ]. The structure of heme C, based upon NMR and IR experiments of the reduced Fe(II) form of the heme, was confirmed in 1975.<ref>{{cite journal | author1=Caughey, W.S.| author2=Smythe, G.A. | author3=O'Keeffe, D.H. | author4=Maskasky, J.E. | author5=Smith, M.L. | year=1975 | title=Heme A of Cytochrome c Oxidase | journal=] | volume=250 | issue=19 | pages=7602–7622 | doi=10.1016/S0021-9258(19)40860-0 | pmid= 170266| doi-access=free }}</ref> The structure of heme C including the absolute ] configuration about the thioether bonds was first presented for the vertebrate protein, cytochrome c<ref>{{cite journal |author1=Takano T. |author2=Trus B.L. |author3=Mandel N. |author4=Mandel G. |author5=Kallai O.B. |author6=Swanson R. |author7=Dickerson R.E. | year=1977 | title=Tuna cytochrome c at 2.0 A resolution. II. Ferrocytochrome structure analysis. | journal=] | volume=252 |issue=2 | pages=776–785 |doi=10.1016/S0021-9258(17)32784-9 | pmid=188826|doi-access=free }}</ref> and is now extended to many other heme C containing proteins.
			==Properties==
⚫	The number of heme C units bound to a holoprotein is highly variable. For vertebrate cells one heme C per protein is the rule but for bacteria this number is often 2, 4, 5, 6 or even 16 heme C groups per holoprotein. It is generally agreed the number and arrangement of heme C groups are related and even required for proper holoprotein function. For instance, those proteins containing several heme C groups are involved with multiple electron transfer reactions, particularly important is the 6 electron reduction required to reduce atmospheric nitrogen into two organic ammonia molecules. It is common for the heme C to amino acid ratio to be high for bacterial ]s, so the interiors of some cytochrome c proteins appear packed with many heme C groups compared with other hemeproteins. Some hemeproteins, often from ]s, may contain five hemes C.<ref name="Gwyer"></ref> The ] is another important enzyme that contains a C type heme.
		⚫	Heme C differs from ] in that the two ] side chains of heme B are replaced by covalent, ] linkages to the ]. The two ] linkages are typically made by cysteine residues of the protein. These linkages do not allow the heme C to easily dissociate from the ], ], compared with the more easily dissociated heme B that may dissociate from the holoprotein, the heme-protein complex, even under mild conditions. This allows a very wide range of cytochrome c structure and function, with myriad c type ] acting primarily as electron carriers. The redox potential for cytochrome c can also be "fine-tuned" by small changes in protein structure and solvent interaction.<ref>{{cite journal | author1=Berghuis, A.M. | author2= Brayer, G.D.| title=Oxidation state-dependent conformational changes in cytochrome c. | journal=J. Mol. Biol.| year=1992 | volume=223 |issue=4 |pages=959–976 | pmid=1311391 | doi=10.1016/0022-2836(92)90255-i}}</ref>
		⚫	The number of heme C units bound to a ] is highly variable. For vertebrate cells one heme C per protein is the rule but for bacteria this number is often 2, 4, 5, 6 or even 16 heme C groups per holoprotein. It is generally agreed the number and arrangement of heme C groups are related and even required for proper holoprotein function. For instance, those proteins containing several heme C groups are involved with multiple electron transfer reactions, particularly important is the 6 electron reduction required to reduce atmospheric nitrogen into two organic ammonia molecules. It is common for the heme C to amino acid ratio to be high for bacterial ]s, so the interiors of some cytochrome c proteins appear packed with many heme C groups compared with other hemeproteins. Some hemeproteins, often from ]s, may contain five hemes C.<ref name="Gwyer">{{cite journal|doi=10.1021/ja054160s | pmid=16248601 | volume=127 | issue=43 | title=Diode or Tunnel-Diode Characteristics? Resolving the Catalytic Consequences of Proton Coupled Electron Transfer in a Multi-Centered Oxidoreductase | year=2005 | journal=Journal of the American Chemical Society | pages=14964–14965 | author=Gwyer James D., Richardson David J., Butt Julea N.}}</ref> The ] is another important enzyme that contains a C type heme.
⚫	The thioether linkages seem to allow a great freedom of function for the holoproteins. In general, the c type cytochromes can be "fine tuned" over a wider range of oxidation-reduction potential than cytochromes b. This may be an important reason why cytochrome c is nearly ubiquitous throughout life. Heme C also plays an important role in ] where just a few molecules of cytoplasmic cytochrome c, which must still contain heme C, leads to programmed cell death.<ref>{{cite journal | doi=10.1039/b717196j | author=Bowman, S.E.J., Bren, K.L.| title=The chemistry and biochemistry of heme C: functional bases for covalent attachment| journal=Nat. Prod. Rep.| year=2008 | volume=25 | issue=6 | pages= 1118–1130 | pmid=19030605 | pmc=2654777 }}</ref>
		⚫	The thioether linkages seem to allow a great freedom of function for the holoproteins. In general, the c type cytochromes can be "fine tuned" over a wider range of oxidation-reduction potential than cytochromes b. This may be an important reason why cytochrome c is nearly ubiquitous throughout life. Heme C also plays an important role in ] where just a few molecules of cytoplasmic cytochrome c, which must still contain heme C, leads to programmed cell death.<ref>{{cite journal | doi=10.1039/b717196j | author=Bowman, S.E.J., Bren, K.L.| title=The chemistry and biochemistry of heme C: functional bases for covalent attachment| journal=Nat. Prod. Rep.| year=2008 | volume=25 | issue=6 | pages= 1118–1130 | pmid=19030605 | pmc=2654777 }}</ref> Cytochrome c can be measured in human serum and can be used as a marker for inflammation.<ref>{{cite journal | author1=Eleftheriadis, T. | author2= Pissas, G.| author3=Liakopoulos, V. | author4=Stafanidis, I. | title=Cytochrome c as a Potentially Clinical Useful Marker of Mitochondrial and Cellular Damage. | journal=Front. Immunol.| year=2016 | volume=7 | pages= 279 | pmid=27489552 | doi=10.3389/fimmu.2016.00279 | pmc=4951490| doi-access= free}}</ref>
⚫	In addition to these covalent bonds, the heme iron is also usually coordinated to two side chains of ]s, making the iron hexacoordinate. For example, mammalian and tuna ] contain a single heme C that is coordinated to side chains of both ] and ].<ref>{{cite journal | author=Yeh, S.R., Han, S., and Rousseau, D.L.| title=Cytochrome c folding and unfolding| journal=Accounts of Chemical Research| year=1998 | volume=31 | issue=11 | pages= 727–735| doi=10.1021/ar970084p}}</ref> Perhaps because of the two covalent bonds holding the heme to the protein the iron of heme C is sometimes ligated with the amino group of ] or even water.
		⚫	In addition to these equatorial covalent bonds, the heme iron is also usually axially coordinated to the side chains of two ]s, making the iron hexacoordinate. For example, mammalian and tuna ] contain a single heme C that is axially coordinated to side chains of both ] and ].<ref>{{cite journal | author=Yeh, S.R., Han, S., and Rousseau, D.L.| title=Cytochrome c folding and unfolding| journal=Accounts of Chemical Research| year=1998 | volume=31 | issue=11 | pages= 727–735| doi=10.1021/ar970084p}}</ref> Perhaps because of the two covalent bonds holding the heme to the protein, the iron of heme C is sometimes axially ligated to the amino group of ] or even water.
⚫	The correct structure of heme C was published, in mid 20th century, by the Swedish biochemist K.-G. Paul.<ref>{{cite journal | doi=10.3891/acta.chem.scand.04-0239 | author=Paul, K.G. | last2=Högfeldt | first2=Erik | last3=Sillén | first3=Lars Gunnar | last4=Kinell | first4=Per-Olof| title=The splitting with silver salts of the cysteine-porphyrin bonds in cytochrome c | journal=Acta Chemica Scandinavica| year=1950 | volume=4 | pages= 239–244}}</ref> This work confirmed the structure first inferred by the great Swedish biochemist ]. The structure of heme C, based upon NMR and IR experiments of the reduced, Fe(II), form of the heme, was confirmed in 1975.<ref>{{cite journal | author=Caughey, W.S. et al. | year=1975 | title=Heme A of Cytochrome c Oxidase | journal=] | volume=250 | pages=7602–7622 | doi=}}</ref> The structure of heme C including the absolute ] configuration about the thioether bonds was first presented for the vertebrate protein<ref>{{cite journal | author=Takano T., Trus B.L., Mandel N., Mandel G., Kallai O.B., Swanson R., Dickerson R.E. | year=1977 | title=Tuna cytochrome c at 2.0 A resolution. II. Ferrocytochrome structure analysis. | journal=] | volume=252 | pages=776–785 | doi= | pmid=188826}}</ref> and is now extended to many other heme C containing proteins.
⚫	==References==
⚫	<references />
	==See also==		==See also==
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	*]		*]
		⚫	==References==
		⚫	<references />
	{{Enzyme cofactors}}		{{Enzyme cofactors}}