EFFECT OF ALPHA-TOCOPHEROL INCORPORATION ON GLUCOSE PERMEABILITY AND PHASE-TRANSITION OF LECITHIN LIPOSOMES

Liposomes were prepared from dipalmitoyllecithin, dimyristoyllecithin, dioleoyllecithin, egg lecithin, and soybean lecithin, and the effects of incorporation of various quantities of α-tocopherol or its analogs on permeability of the liposomes to glucose were studied at various temperatures (4-40°C). Results showed that increase in the quantity of α-tocopherol incorporated into dipalmitoyllecithin and dimyristoyllecithin liposomes lowered the transition temperature for marked release of glucose and also decreased the maximum rate of temperature-dependent permeability. α-Tocopherol also had similar but less marked effects on the permeability of dioleoyllecithin and egg lecithin liposomes, but little effect on those of soybean lecithin, which has a higher degree of unsaturation. In dipalmitoyllecithin liposomes phytol showed a similar effect on permeability to that of α-tocopherol, but phytanic acid caused a different pattern of temperature-dependent permeability. With analogs of α-tocopherol, the regulatory effect on permeability decreased with shortening and disappearance of the isoprenoid side chain. The significance of these observations is discussed in relation to the physiological functions of tocopherols in natural membranes. © 1979.