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The in vitro conversion of 14C-labeled leucine, isoleucine, and pyruvate to specific lipids was compared in rat aorta, diaphragm, anf fat pad. Total lipid specific radioactivity from all precursors was greatest in aorta. The ratio of label incorporated into polar lipids vs. neutral lipids by aorta was generally several-fold that incorporated by muscle and fat pad. The labeling of sterols in the aorta from 14C-leucine and pyruvate was equivalent. It is concluded that leucine may be a substantial precursor to polar lipids and to sterols in rat aorta.

The in vitro incorporation of lucine, isoleucine and pyruvate into lipids was compared and the possibility that leucine might serve as an in situ precursor to the corresponding iso fatty acids in the rat sciatic nerve was studied. The relative incorporation of 14C from leucine into lipids vs. nonlipids was 20%, and the incorporation of label into total lipids from leucine was one-halp that from pyruvate. The incorporation of label from leucine and pyruvate into sterols was nearly equivalent, but the incorporation of label into all other lipid classes from leucine was less than that from pyruvate, and the incorporation of label from isoleucine into lipids was much less in all cases. No detectable label from leucine was incorporated into brached chain fatty acids. It is concluded that leucine may be a substantial in vitro precursor to all major lipids in peripheral nerve, espeically sterols. The possibility and significance of a leucine catabolic pathway in the cytosol in relation to availability of 3-hydroxy-3-methylglutaryl CoA for sterol biosynthesis is discussed.

Fatty acid methyl esters were prepared from spadefish (Chaetodipterus faber) liver oil and were analyzed by open tublar gas chromatography. The unusual fatty acid trans-6-hexadecenoic acid was identified as a major monoenoic component by reductive ozonolysis and by mass spectrometry of the di-trimethylsilyl ether. Very minor amounts of 7-methyl-7-hexadecenoic acid were found.

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