Active oxygen chemistry within the liposomal bilayer. Part III: Locating Vitamin E, ubiquinol and ubiquinone and their derivatives in the lipid bilayer.
We have previously shown that the location and orientation of compounds intercalated within the lipid bilayer can be qualitatively determined using an NMR chemical shift-polarity correlation. We describe herein the results of our application of this method to analogs of Vitamin E, ubiquinol and ubiquinone. The results indicate that tocopherol--and presumably the corresponding tocopheroxyl radical--reside adjacent to the interface, and can, therefore, abstract a hydrogen atom from ascorbic acid. On the other hand, the decaprenyl substituted ubiquinol and ubiquinone lie substantially deeper within the lipid membrane. Yet, contrary to the prevailing literature, their location is far from being the same. Ubiquinone-10 is situated above the long-chain fatty acid "slab". Ubiquinol-10 dwells well within the lipid slab, presumably out of "striking range" of Vitamin C. Nevertheless, ubiquinol can act as an antioxidant by reducing C- or O-centered lipid radicals or by recycling the lipid-resident tocopheroxyl radical.
Afri
Michal
M
Department of Chemistry, Bar-Ilan University, Ramat Gan 52900, Israel.
Ehrenberg
Benjamin
B
Talmon
Yeshayahu
Y
Schmidt
Judith
J
Cohen
Yael
Y
Frimer
Aryeh A
AA
D000975:Antioxidants / Q000378:metabolism / Q000494:pharmacology; D001205:Ascorbic Acid / Q000737:chemistry / Q000378:metabolism; D005609:Free Radicals / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D017382:Reactive Oxygen Species / Q000737:chemistry*; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism*; D014810:Vitamin E / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D000975:Antioxidants; D005609:Free Radicals; D008051:Lipid Bilayers; D008081:Liposomes; D017382:Reactive Oxygen Species; D014867:Water; D014451:Ubiquinone; D014810:Vitamin E; C003741:ubiquinol; D001205:Ascorbic Acid