title: Localization of coenzyme Q10 in the center of a deuterated lipid membrane by neutron diffraction.
abstract: Quinones (e.g., coenzyme Q, CoQ10) are best known as carriers of electrons and protons during oxidative phosphorylation and photosynthesis. A myriad of mostly more indirect physical methods, including fluorescence spectroscopy, electron-spin resonance, and nuclear magnetic resonance, has been used to localize CoQ10 within lipid membranes. They have yielded equivocal and sometimes contradictory results. Seeking unambiguous evidence for the localization of ubiquinone within lipid bilayers, we have employed neutron diffraction. CoQ10 was incorporated into stacked bilayers of perdeuterated dimyristoyl phosphatidyl choline doped with dimyristoyl phosphatidyl serine containing perdeuterated chains in the natural fluid-crystalline state. Our data show CoQ10 at the center of the hydrophobic core parallel to the membrane plane and not, as might be expected, parallel to the lipid chains. This localization is of importance for its function as a redox shuttle between the respiratory complexes and, taken together with our recent result that squalane is in the bilayer center, may be interpreted to show that all natural polyisoprene chains lie in the bilayer center. Thus ubiquinone, in addition to its free radical scavenging and its well-known role in oxidative phosphorylation as a carrier of electrons and protons, might also act as an inhibitor of transmembrane proton leaks.
authors.affiliation: Hahn-Meitner Institute, Berlin Neutron Scattering Centre, Glienicker Strasse 100, D-14109 Berlin, Germany; Darmstadt University of Technology, Dept. of Chemistry, Physical Biochemistry, Petersenstrasse 22, D-64287 Darmstadt, Germany. hauss@hmi.de
authors.forename: Thomas
authors.initials: T
authors.lastname: Hauss
authors.forename: Silvia
authors.initials: S
authors.lastname: Dante
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Haines
authors.forename: Norbert A
authors.initials: NA
authors.lastname: Dencher
mesh_terms: D003067:Coenzymes; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism*; D033363:Neutron Diffraction; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry
chemical_list: D003067:Coenzymes; D008051:Lipid Bilayers; D014451:Ubiquinone; C024989:coenzyme Q10