title: Menaquinone-7 is specific cofactor in tetraheme quinol dehydrogenase CymA.
abstract: Little is known about enzymatic quinone-quinol interconversions in the lipid membrane when compared with our knowledge of substrate transformations by globular enzymes. Here, the smallest example of a quinol dehydrogenase in nature, CymA, has been studied. CymA is a monotopic membrane tetraheme c-type cytochrome belonging to the NapC/NirT family and central to anaerobic respiration in Shewanella sp. Using protein-film electrochemistry, it is shown that vesicle-bound menaquinone-7 is not only a substrate for this enzyme but is also required as a cofactor when converting other quinones. Here, we propose that the high concentration of quinones in the membrane negates the evolutionary pressure to create a high affinity active site. However, the instability and reactivity of reaction intermediate, semiquinone, might require a cofactor that functions to minimize damaging side reactions.
authors.affiliation: Institute of Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, United Kingdom.
authors.forename: Duncan G G
authors.initials: DG
authors.lastname: McMillan
authors.forename: Sophie J
authors.initials: SJ
authors.lastname: Marritt
authors.forename: Julea N
authors.initials: JN
authors.lastname: Butt
authors.forename: Lars J C
authors.initials: LJ
authors.lastname: Jeuken
mesh_terms: D020134:Catalytic Domain; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003574:Cytochrome c Group / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods; D004566:Electrodes; D004579:Electron Transport; D004583:Electrons; D006860:Hydrogen Bonding; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D010084:Oxidation-Reduction; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000737:chemistry*; D011487:Protein Conformation; D024482:Vitamin K 2 / Q000737:chemistry*
chemical_list: D003574:Cytochrome c Group; D024482:Vitamin K 2; C017165:cytochrome c(3); D000587:Oxidoreductases Acting on CH-NH Group Donors; C069539:quinoline dehydrogenase