The properties of polyunsaturated lecithins in monolayers and liposomes and the interactions of these lecithins with cholesterol

Publisher Summary This chapter discusses the metabolism of molecular species of diacylglycerophospholipids. The glycerolipid composition of cell membranes and lipoproteins is metabolically adjusted to meet specific requirements, and it does not merely reflect the supply of different fatty acids in the diet or in the cell culture medium. However, adequate adjustment cannot always be possible, and under such conditions, the cellular activity can take place in a suboptimal physicochemical environment and characteristic symptoms of a disease state can appear. As the cellular lipid composition is subject to considerable dietary and pharmacological manipulation, there can be therapeutic alterations in the composition of the molecular species of the tissues and other animal species. The metabolism of the molecular species of the glycerophospholipids is intimately involved with the activity of the acyl transferases. Therapeutic alterations in the composition of the molecular species of the glycerolipids can be feasible and can yield beneficial results in the treatment of membrane diseases.

Metabolism of molecular species of diacylglycerophospholipids.

The Physical State of Phospholipids and Cholesterol in Monolayers, Bilayers, and Membranes

The thermotropic properties of aqueous dispersions of synthetic mixed-acid polyunsaturated 1,2-diacyl-3-sn-phosphatidylcholines (PC) have been studied by differential scanning calorimetry. The gel to liquid-crystalline phase transition temperature (Tc) of 1-stearoyl-2-linoleoyl-sn-glycero-3-phosphocholine (SLPC) was -16.2 +/- 1.6 degrees C (means +/- SD, nine dispersions, three separate synthetic preparations); that for a preparation of 1-stearoyl-2-linolenoyl-PC (SLnPC) was -13 degrees C and for a preparation of 1-stearoyl-2-arachidonoyl-PC (SAPC) was -12.6 +/- 1.0 degrees C (three dispersions, one preparation). The temperatures of maximum heat flow (Tmax) for the lipid transitions were -14.4 +/- 1.3, -11, and -10.7 +/- 0.9 degrees C and the enthalpies were 3.3 +/- 1.0, 6.6, and 5.3 +/- 1.8 kcal X mol-1 for SLPC, SLnPC, and SAPC, respectively. The transition temperatures and enthalpies are rationalized on the basis of existing data on the effect of double-bond position on Tc and are interpreted with the use of a statistical mechanical model. The trend of the transition temperatures with the introduction of multiple double bonds reflects opposing effects due to increased molecular area and decreasing degrees of freedom of rotation about carbon-carbon bonds.

J. Tinoco

Papers

Interactions between cholesterol and lecithins in monolayers at the air-water interface