ESR and monolayer study of the localization of coenzyme Q10 in artificial membranes

The data obtained from the ESR experiments show a complex, depth dependent effect of CoQ10 on the lipid molecules mobility in the bilayer. These effects depend both on its concentration and the temperature. CoQ10 disturbs not only the hydrophobic core of the membrane but also the region close to the hydrophilic headgroups of phospholipids. Both these effects could be explained by the fact that the high hydrophobicity of CoQ10 causes the molecules to position itself in the interior of the bilayer, but at the same time its water seeking headgroup is located close to the region of the polar headgrops of membrane lipids. The presence of CoQ10 in the hydrophobic core has further implications on the properties of membrane intrinsic domain. Results of monolayer experiments indicate that CoQ10 may form aggregates when mixed with PC molecules in the lipid hydrocarbon chain-length dependent manner. CoQ10 is not fully miscible with DMPC or DPPC but it is well miscible with the long-chain DSPC molecules. Our suggestion is that CoQ10 when present in long-chain phospholipid bilayer, interacts with saturated fatty acyl-chains and adapt the structure which allows such interactions: either parallel to the saturated acyl chains or "pseudo-ring" conformation resembling sterol structure.