| As said above the human desaturase is unable to introduce double bonds beyond C-9. On the other hand, two types of fatty acids - those having double bonds 3 carbons from the methyl end (ω-3 fatty acids) and 6 carbons from the methyl end (ω-6 fatty acids) - are required for the synthesis of eicosanoids (C-20 fatty acids), precursors of important molecules such as prostaglandins, thromboxanes and leukotrienes. Therefore, the ω-3 and ω-6 fatty acids (or their precursors) must be supplied with diet. As it happens, they are obtained from dietary vegetable oils which contain the ω-6 fatty acid, linoleic acid (C-18:2, Δ9,12) and the ω-3 fatty acid, linolenic acid (C-18:3, Δ9,12,15). Linoleic acid is converted in a series of elongation and desaturation reactions to arachidonic acid (C-20:4, Δ5,8,11,14), the precursor for the synthesis of other eicosanoids in man. Elongation and desaturation of linolenic acid produces eicosapentaenoic acid (EPA; C-20:5, Δ5,8,11,14,17), which is a precursor of yet another series of eicosanoids.
|
