2 Fatty Acid Desaturation

Abstract

Publisher Summary This chapter focuses on the desaturation of fatty acids in animal liver and summarizes the desaturation process in other systems. Fatty acids of dietary or endogenous origin may be extensively modified in the animal by a combination of desaturation and chain elongation. These two processes can be used alternately to produce longer-chain polyunsaturated fatty acids. The desaturation of saturated or unsaturated fatty acids can be measured by the use of the appropriate radioactive fatty acid. The routine assay for stearoyl-CoA desaturase activity in the microsomal fraction of animal systems uses the [l- 14 C]fatty acyl-CoA derivative and NADH. After a 5–15 min incubation, the reaction is terminated with NaOH, the mixture is saponified, and the liberated fatty acids are extracted and separated, as their methyl esters, by thin-layer chromatography on silver nitrate-impregnated silica gel. When the substrate to be desaturated is an unsaturated fatty acid, the resolution of the polyunsaturated fatty acid mixture is performed by gas–liquid chromatography. The desaturation process has also been assayed by monitoring the release of 3 H 2 O from [9, 10- 3 H]stearoyl-CoA. The initial studies on stearic acid desaturation in animal systems showed that the fatty acid could be desaturated when it was in the form of the CoA ester or when the incubation system contained ATP, CoA, and Mg. These results suggest that the true substrate was the CoA ester, which is confirmed by analyzing the incubation mixture for radioactive lipid species.