Biochemistry

With a deficiency of choline, the synthesis of phospholipids from neutral fat decreases sharply or stops at all, and neutral fat is deposited in the liver, that is, fatty infiltration of this organ occurs, which threatens to switch into its fatty dystrophy. It is prevented by lipotropic substances (choline, methionine and other sources of methyl groups) contained in cottage cheese and other dairy products, meat, etc. 10.2 LIPIDS METABOLISM IN TISSUES Lipid metabolism in tissues is the most biologically important step in their transformation. At this phase, lipids are assimilated as a plastic material and are split with the release of energy. The main endogenous source of lipids, which play the role of a metabolic fuel, is the reserve fat contained in the protoplasm of cells in the form of droplets. For this purpose, membrane phospholipids are also used. In the "fat depot" with the participation of tissue lipases is the hydrolysis of simple fats to glycerol and free fatty acids take place. Glycerol is phosphorylated by ATP, through a series of intermediate reactions is converted to phosphoglycerol aldehyde, which is then oxidized during glycolysis to phosphoglycerol and pyruvic acids. The latter, undergoing oxidative decarboxylation, is converted to acetyl- CoA, which is oxidized to CO 2 and H 2 O in the tricarboxylic acid cycle. In the form of a complex with albumin, free fatty acids with the blood flow into organs and tissues, where the complex breaks down, and fatty acids either undergo P-oxidation, or are used in the synthesis of triacylglycerols, cholesterol, glycerophospholipids, sphingolipids, etc. P- Oxidation of higher fatty acids The theory of oxidation of higher fatty acids was advanced by A. Knoop in 1904. He suggested that the oxidation of fatty acid molecules in the tissues of the body occurs in the P-position by successive cleavage of the fatty acid molecule from the carboxyl group of two carbon fragments. In this regard, the process of oxidation of fatty acids is called p-oxidation. Since any fatty acid that is part of natural fats has an even number of carbon atoms, cleavage of a carbon pair in each reaction necessarily leads the process to the formation of butyric acid. After the next cycle of p-oxidation, it turns into acetoacetic acid, which hydrolyzes to two acetic acid molecules. This theory has not lost its significance to the present and is the basis of modem ideas about the mechanism of oxidation of higher fatty acids. P-oxidation of higher fatty acids occurs in the mitochondria of cells with the participation of a multienzyme complex. 195