Studies on the distribution of free carnitine and the occurrence and nature of bound carnitine

Abstract

The distribution of carnitine in various tissues of the rat was investigated, using modifications of existing assays. Muscle showed about 120–180 μ./g. wet weight; brain, 20 μg.; liver 60–90 μg.; testes, 115 μg. Various treatments with organic solvents and acids released no increased amounts of carnitine. All carnitine was dialyzable. No “bound carnitine,” therefore, was detectable in mammalian tissue. This result was confirmed by injection of labeled carnitine, using a radiochemical assay, in combination with the chemical assay. Developing chick embryos showed a great increase in carnitine between the 12th and 16th day (about 175 and 850 μg. per whole egg, respectively). It was found that yolk sac contained about 40–50% of the carnitine of whole egg, and that some of this, about 20–45%, was in a bound form, released by acid treatment and nondialyzable. Specific extraction procedures, followed by hydrolysis, showed this “bound carnitine” to be combined in phospholipid. This finding was confirmed with labeled carnitine. Labeled phospholipid was extractable from the yolk sac, and was purified by silicic acid chromatography. A labeled carnitine-contaming phospholipid emerged with the lecithin fraction. The hypothesis is proposed that this material is phosphatidylearnitine.