Biochemistry and Molecular Biology - Belyasova N.A. 2002

Metabolism. Energy-requiring processes
Lipid Biosynthesis
Formation of Unsaturated Fatty Acids

Unsaturated Fatty acids are synthesized from saturated ones with a corresponding chain length. In aerobic organisms, The formation of a double bond is catalyzed by the enzyme acyl-CoA oxidase, and oxidation proceeds According to the reaction

Class="center">Пальмитоил-СоА + NADPH + H⁺ + O₂ →

→ Пальмитолеил-СоА + NADP⁺ + 2 H₂O

This process involves the simultaneous oxidation of two different substrates: a fatty acid (where a double bond is formed) and NADPH, catalyzed by Monooxygenases known as desaturases. Another mechanism for introducing double bonds into fatty acid molecules is also known, which does not require molecular oxygen. For example, in E. coli Cells, the synthesis of palmitoleic acid begins right at the fatty acid synthase stage with the formation of a double bond within the C₁₀ fragment. This reaction involves a special enzyme present in the Cells of the bacterium—β-hydroxydecanoyl thioether dehydratase—which catalyzes the formation of a cis-β,γ-double bond rather than a trans-α,β-bond, as occurs during the enoyl-derivative formation stage in saturated fatty acid synthesis. Subsequently, the unsaturated fragment is elongated into C₁₆ and C₁₈ derivatives.

In animals and plants, the Introduction of the first double bond into a saturated fatty acid molecule is readily accomplished in the Cytosol. The formation of additional double bonds occurs in The Endoplasmic reticulum in plants, whereas in animals it does not occur at all. Therefore, polyunsaturated fatty acids (such as linoleic and linolenic acids) are essential components for animals, particularly mammals, and must be obtained from dietary sources (of plant origin). These fatty acids serve as precursors for the Synthesis of Other polyunsaturated fatty acids. A deficiency of linoleic and linolenic acids in the animal diet leads to growth retardation, Skin and Kidney lesions, and reproductive disorders.