Application of GC/MS to Fatty Acid Metabolism

Abstract

Mass spectrometry has been developed to characterize the chemical structure of organic compounds. Gas chromatography mass spectrometry (GC/MS) is suitable for the characterization of biological materials in a very small amount. Mass fragmentography is a sensitive and specific method for quantitative determination of such materials. The present paper describes applications of these techniques to the analysis of fatty acid metabolism in the Harderian gland of guinea pig. More than 90% of total lipids was identified as 1-0-alkyl2, 3-di-O-acylglycerol. The alkyl and acyl moieties consisted of saturated aliphatic chains ranging from 14 to 21 carbon atoms and 15 to 26 carbon atoms, respectively. About 60 mole %of them had methyl branches, which were located at the even-numbered carbon atoms. Fatty acid synthetase was isolated from this gland and analyzed by a new assay method for fatty acid synthetase using mass fragmentography. This enzyme produced many oddnumbered and methyl-branched fatty acids in the presence of methylmalonyl-CoA. These fatty acids are characteristic components of the lipid secreted from this gland. Substrate level regulation was demonstrated. The availability of methylmalonyl-CoA regulates the composition of fatty acids produced by the fatty acid synthetase from this gland. In the presence of acetyl-CoA, propionyl-CoA, malonyl-CoA, and methylmalonyl-CoA in appropriate concentrations the enzyme can produce the proper fatty acids needed for the synthesis of the 1-0-alkyl-2, 3-di-O-acylglycerol, especially for the acyl chain at the 2-position. Same procedures are also applicable to the diagnosis of congenital lipid metabolism, cerebrotendinous xanthomatosis, by quantitating cholestanol and bile acids in serum.