Hauss Thomas, Dante Silvia, Haines Thomas H, Dencher Norbert A
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.
Biochim Biophys Acta. 2005 Nov 15;1710(1):57-62. doi: 10.1016/j.bbabio.2005.08.007. Epub 2005 Sep 19.
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.
醌类物质（如辅酶Q，CoQ10）最为人所知的是在氧化磷酸化和光合作用过程中作为电子和质子的载体。大量主要更为间接的物理方法，包括荧光光谱法、电子自旋共振法和核磁共振法，已被用于在脂质膜中定位CoQ10。这些方法得出了模棱两可、有时甚至相互矛盾的结果。为了寻找关于泛醌在脂质双层中定位的确凿证据，我们采用了中子衍射法。CoQ10被掺入到天然流体结晶态的、掺有含全氘化链的二肉豆蔻酰磷脂酰丝氨酸的全氘化二肉豆蔻酰磷脂酰胆碱的堆叠双层中。我们的数据显示CoQ10位于疏水核心的中心，与膜平面平行，而不是如预期的那样与脂质链平行。这种定位对于其作为呼吸复合物之间的氧化还原穿梭体的功能很重要，并且结合我们最近关于角鲨烷位于双层中心的结果，可以解释为表明所有天然聚异戊二烯链都位于双层中心。因此，泛醌除了具有清除自由基的作用以及在氧化磷酸化中作为电子和质子载体的众所周知的作用外，还可能充当跨膜质子泄漏的抑制剂。
