The structure and abundance of rat tissue cardiolipins

Abstract

Cardiolipins of rat tissues were isolated by column chromatography and analyzed. The P content ranged from 2.61% to 3.64%. The ester:P ratio varied from 1.63 to 2.09, and the glycerol:P ratios varied from 1.34 to 1.68. The fatty acid spectrum of the tissue cardiolipins showed some, like heart, kidney and liver to be highly unsaturated and others like brain, lung and testis to be highly saturated. Analysis of the fatty acids released by phospholipase A demonstrated that certain fatty acids are preferentially β-linked, but on the whole, the fatty acid distribution is much more random than that of other phospholipids, like the lecithins. All the rat tissue cardiolipins are degraded by hot acetic acid to yield diglycerides, very small amounts of monoglycerides, and other P-containing products. However, only with rat-liver cardiolipin, beef-heart cardiolipin, and a synthetic cardiolipin are appreciable amounts of water-soluble P released. On treatment with sodium methoxide at 0° all rat tissue cardiolipins give rise to 4–6 lyso-derivatives resulting from the sequential loss of one or more fatty acids. All cardiolipins are eventually completely degraded to fatty acid methyl esters, a water-soluble P compound and smaller amounts of other products including free fatty acids and vitamin A. In the case of rat-liver cardiolipin, alkaline hydrolysis yields vitamin A but not in stoichiometric amount. All cardiolipins react with [ 14C]acetic anhydride to yield a radioactive acetylated derivative. The results of this investigation show that whereas beef-heart cardiolipin has a structure consistent with the recently synthesized cardiolipin, the cardiolipins of rat tissues are not consistent with this structure. New provisional structures for the rat tissue cardiolipins are proposed in which one of the phosphate groups bears a third moiety (such as vitamin A) as a tertiary phosphate ester or the phosphate group bears a fatty acid as a mixed carboxylic acid-phosphoric acid anhydride.