Phospholipids of outer mitochondrial membranes. Effect of ascorbate on their polyunsaturated fatty acids

Abstract

Isolated outer mitochondrial membranes from rat liver undergo alterations in their lipid composition when they are incubated in the presence of 1 mM ascorbate. Polyun­ saturated fatty acids which form part of the phospholipids are altered through per­ oxidation reactions; through the altered fatty acids stable bonds are established between proteins and lipids, leading to a decrease in phospholipids in the total lipid extract. Saturated and monounsaturated fatty acids which accompany polyunsaturated fatty acids in the different phospholipids can be recovered in the protein precipitate after having removed all the extractable lipids. A consideration of the losses of the fatty acids in the different phospholipids and their reovery in the protein fractions has allowed to reach some conclusions with respect to the existence of certain specific associations of fatty acids within each type of phospolipid. The data presented indicate the existence of two types’ of phospholipids in the outer membrane regarding the nature of their fatty acid constituents. A group of molecules would contain both a saturated and an unsaturated fatty acid, whereas another group would contain only saturated fatty acids. With the only exception of phosphatidylinositol, all the phospholipids contain palmitic acid in a much higher proportion than stearic acid.