Interactions of tocopherols and ubiquinones with monolayers of phospholipids

Abstract

1. The penetration of alpha-tocopherol and seven of its derivatives, and five compounds in the ubiquinone series, having differing chain lengths, into monolayers at the air/water interface of 11 different synthetic phospholipids and cholesterol was investigated; the properties of mixed monolayers of the tocopherols and of ubiquinones with phospholipids were also studied. 2. Penetration of alpha-tocopherol into diarachidonylglycerylphosphorycholine was approximately constant for molar ratios of tocopherol/phospholipid ranging from 0.4:1.0 to 2.0:1.0. 3. Tocopherols with shorter or longer side chains than alpha-tocopherol had a lesser ability to penetrate monolayers of phospholipid molecules with 16 or more carbon atoms in their acyl chains. 4. All the tocopherols penetrated more readily as unsaturation in the phospholipids was increased, and their penetration into mixed monolayers of phospholipids was greatly facilitated by the presence of relatively small quantities of unsaturated phospholipid molecules. 5. There was relatively little interaction between the tocopherols and cholesterol, or between the ubiquinones and phospholipids. 6. The possible significance of the observed interactions between alpha-tocopherol and polyunsaturated phospholipids is discussed in relation to the biochemical actions of alpha-tocopherol in vivo. 7. It is suggested that fluidity of the lipid bilayer in membranes containing polyunsaturated phospholipids may allow alpha-tocopherol to interact in a dynamic manner with a number of phospholipid molecules.

Structures and properties of mixtures of branched chain compounds and lecithin: phytol, α-tocopherol (vitamin E), and phytanic acid

“…Such behaviour has been correlated with a decrease in permeability above T, (12,27). Very recently the monolayer behaviour of vitamin E in lecithin monolayers has been studied (28). It was found that in monolayers of distearoyl-or dioleoyllecithin the additivity rule was well followed, up to 50 molz incorporated a-tocopherol.…”

Induction of membrane fusion by polysialogangliosides

“…Conversely, lipids chemically similar to those but not showing these type of interactions are ineffective as fusogenics [2,3]. On this basis it was surmised that a reduction of the electrostatic field perpendicular to the surface of the lipid bilayer induced by a lipid or a water-soluble substance is a key event for the initial increase of the membrane permeability and aggregation that leads to membrane fusion [6,7].…”

The location and behavior of α‐tocopherol in membranes

“…More than 30 years ago Lucy [34] proposed on the basis of molecular models that the conformation of the multiple double bonds in the PUFA chains of arachidonic acidcontaining phospholipids creates pockets that can accommodate the methyl groups at positions 4 0 and 8 0 on the isoprenoid side chain of a-tocopherol, resulting in the formation of complexes between the two molecules that are ideally suited to preventing the oxidation of the highly vulnerable fatty acid. Experimental support was sparse and indirect, consisting of easier penetration of a-tocopherol into monolayers containing unsaturated phospholipid [35] and a reduction in permeability by a-tocopherol of membranes containing arachidonic acid [36]. Later it was shown using DSC that increasing amounts of a-tocopherol broadened and lowered the phase transition temperature of PUFAcontaining PC samples, which was interpreted as being due to fluid phase immiscibilities and lateral phase separation of domains containing differing amounts of a-tocopherol [37].…”