ABSTRACT
Natural essential fatty acids (EFA) of the animal kingdom are traditionally regarded as the unsaturated fatty acids linoleic and α-linolenic that cannot be synthesized de novo by animals and the fatty acids derived from them. That is, plants synthesize de novo linoleic and α-linolenic acids and animals convert them to fatty acids that are more unsaturated and of longer chain length. However, there are exceptions to these general rules. The sequence of reactions involved in the biosynthesis of long-chain unsaturated fatty acids derived from linoleate and α-linolenate was shown in experiments done both in vivo and in vitro. They are the result of coordination between two types of reactions: desaturation at specific positions of the hydrocarbon chain and elongation by addition of units of two carbon atoms. The reactions are catalyzed by enzymes which are integral parts of the endoplasmic reticulum membrane. 1,5 The same enzymes are involved in the biosynthesis of fatty acids derived from linoleate, α-linolenate, oleate, and palmitoleate. 5 The fatty acids derived from each one of these precursors constitutes a family. Each family is independent and there is no direct crossover. Fatty acids of the linoleic acid (ω6) family cure the typical symptoms produced in the rat and other animals by a fat-free diet. 6 The major symptoms produced in the rat by EFA deficiency are dermatosis and increased water permeability of the skin, decrease in weight, decreased capillary resistance, cholesterol accumulation in lung, impaired reproduction and lactation in females and degeneration of seminiferous tubules of males, alteration of endocrine glands, changes in the fatty acid composition of tissues, modification of cholesterol levels in organs and plasma, swelling of mitochondria, and increased triacylglycerol synthesis by the liver. α-Linolenic acid is not able to cure the skin signs.
