Comparison of phosphatidylcholines containing one or two docosahexaenoic acyl chains on properties of phospholipid monolayers and bilayers.

Docosahexaenoic acid (DHA) is the longest and most unsaturated of the n - 3 fatty acids found in membranes. Although a number of membrane properties have been demonstrated to be affected by the presence of this fatty acid, its mode of action has yet to be clearly elucidated. Prior reports on biological membranes have not distinguished the effect of mono-docosahexaenoyl phospholipids from those caused by phospholipids containing docosahexaenoic acid in both chains. This report compares properties of monolayers and bilayers composed of either 1-stearoyl-2-linolenoyl-sn-glycero-3-phosphocholine (as a control), 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine or 1,2-di-docosahexaenoyl-sn-glycero-3-phosphocholine. When compared to the mono-DHA phosphatidylcholine (PC), the di-DHA PC occupies a much larger area/molecule, supports a more fluid and permeable bilayer, and is less susceptible to peroxidation. Monolayers made from either phospholipid are not condensable by cholesterol. We suggest many of the membrane properties linked to the presence of DHA may be the result of phospholipids which have lost their normal positional selectivity and have incorporated DHA into both positions.