title: EPR detection of an O(2) surrogate bound to heme c(n) of the cytochrome b(6)f complex.
abstract: The ligand-binding properties of the unique heme c(n) of the cyt b(6)f complex, which is bridged to the heme b(n), are studied with EPR spectroscopy. Despite an open coordination site, high-spin heme c(n) in the oxidized state does not bind typical heme ligands such as cyanide, indicating their inaccessibility to the heme. In the reduced state, heme c(n) binds the O(2) surrogate NO to give a five-coordinate S = (1)/(2) [FeNO](7) complex, indicating that the site is accessible in the reduced state of the protein. The binding of NO implies that the heme c(n) can also bind O(2). Given the significant number of experimentally documented pathways for which a plastoquinol oxidase has been proposed, but the actual oxidase not identified, it is proposed that one of the functions of heme c(n), the only prosthetic group in the electron transport chain with oxidase-like properties, is the putative oxidase.
authors.affiliation: Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Anna I
authors.initials: AI
authors.lastname: Twigg
authors.forename: Danas
authors.initials: D
authors.lastname: Baniulis
authors.forename: William A
authors.initials: WA
authors.lastname: Cramer
authors.forename: Michael P
authors.initials: MP
authors.lastname: Hendrich
mesh_terms: D045346:Cytochrome b6f Complex / Q000737:chemistry / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000031:analogs & derivatives* / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D010100:Oxygen / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D008024:Ligands; C031690:heme C; D006418:Heme; D045346:Cytochrome b6f Complex; D010100:Oxygen
references.citation: Biochim Biophys Acta. 2008 Mar;1777(3):269-76
references.pmid: 18241667
references.citation: Biochemistry. 1992 Mar 24;31(11):2847-9
references.pmid: 1348002
references.citation: Annu Rev Genet. 2008;42:463-515
references.pmid: 18983262
references.citation: Annu Rev Plant Biol. 2002;53:523-50
references.pmid: 12227339
references.citation: J Mol Biol. 2007 Jun 29;370(1):39-52
references.pmid: 17498743
references.citation: J Am Chem Soc. 2006 Nov 8;128(44):14246-7
references.pmid: 17076484
references.citation: Proc Natl Acad Sci U S A. 2007 Jan 9;104(2):519-24
references.pmid: 17202266
references.citation: Biochim Biophys Acta. 2006 May-Jun;1757(5-6):339-45
references.pmid: 16787635
references.citation: Science. 2003 Nov 7;302(5647):1009-14
references.pmid: 14526088
references.citation: J Biol Chem. 2009 Apr 10;284(15):9861-9
references.pmid: 19189962
references.citation: Proc Natl Acad Sci U S A. 2008 Jun 3;105(22):7881-6
references.pmid: 18511560
references.citation: Biochim Biophys Acta. 1973 May 30;305(2):329-52
references.pmid: 4200351
references.citation: Proc Natl Acad Sci U S A. 2005 Nov 1;102(44):15860-5
references.pmid: 16247018
references.citation: Photosynth Res. 2007 Jul-Sep;93(1-3):69-77
references.pmid: 17279442
references.citation: Annu Rev Biochem. 2000;69:1005-75
references.pmid: 10966481
references.citation: J Biol Chem. 2008 Feb 1;283(5):2846-57
references.pmid: 18039651
references.citation: Biochemistry. 2004 Dec 28;43(51):16329-36
references.pmid: 15610027
references.citation: J Am Chem Soc. 2005 Dec 21;127(50):17634-43
references.pmid: 16351093
references.citation: Annu Rev Biochem. 2006;75:769-90
references.pmid: 16756511
references.citation: Nature. 2003 Nov 27;426(6965):413-8
references.pmid: 14647374
references.citation: J Am Chem Soc. 2001 Feb 21;123(7):1513-4
references.pmid: 11456732
references.citation: Annu Rev Plant Physiol Plant Mol Biol. 1996 Jun;47:477-508
references.pmid: 15012298
references.citation: J Biol Chem. 2000 Jun 9;275(23):17256-62
references.pmid: 10748104
references.citation: Proc Natl Acad Sci U S A. 1982 Jul;79(14):4352-6
references.pmid: 16593210