A oxidation of fatty acids

In the course of an investigation into the nature of the biosynthetic intermediate of long chain fatty aldehydes, Hitchcock and James proposed that the (S)-2-hydroxy-fatty acid serves as an intermediate in the a-oxidation of fatty acids (40-41). On the other hand, another mechanism for a-oxidation of fatty acids in peanut cotyledons has been proposed by Shine and Stumpf (34), involving hydroperoxy-fatty acids rather than the hydroxy-fatty acids as a transitory intermediate. However, the hydroperoxy intermediate has not been studied so far in marine algae. 

See also Fatty Acids, Coenzyme A, Oxidation of Fatty Acids, Fat Synthesis, Elongation of Fatty Acids, Fatty Acid Desaturation, Thiolase... 

Poulos, A., Sharp, R, Singh, H., Johnson, D.W., Carey, W.F. Easton, C. (1993) Biochem. J. 292, 457-461. Formic acid is a product of the a-oxidation of fatty acids by human skin fibroblasts deficiency of formic acid production in peroxisome-deficient fibroblasts. 

Hamberg, M Sanz, A Gastresana, G. a-Oxidation of fatty acids in higher plants Identification of a pathogen-inducible oxygenase (PIOX) as an a-dioxygenase and biosynthesis of 2-hydroperoxylinolenic acid. J. Biol Chem., 1999, 274, 24503-24513. 

Figure 11.6 a-Oxidation of fatty acids in plants. Adapted from Galliard (1980). 

Enzymatically active materials (fruits, vegetables and some fats) contain a large number of other aldehydes that are produced from essential fatty acids, mainly linoleic and Knolenic acids (Table 8.9) by oxidation reactions catalysed by lipoxygenases. In some vegetables (e.g. in cucumbers), aldehydes also result from a-oxidation of fatty acids (Figure 8.15). The primary oxidation products of essential fatty acids are hydroperoxides, which break down to aldehydes and other products under the action of lyases and can be... 

Figure 8.15 Formation of aldehydes by a-oxidation of fatty acids.

Gurr" has reviewed recent studies in the biosynthesis of polyunsaturated acids in plants. Other workers from the same laboratory conclude that there are two routes for the a-oxidation of fatty acids in leaves the quicker and major pathway proceeds through the 2L-hydroxy-acid the slower and minor pathway proceeds through the 2D-enantiomer. 

Place of the fats in total metabolism (Fig. 74). In conclusion let us summarize the position of the biosynthesis of fats in total metabolism their glycerol component originates from dihydroxyacetone phosphate and their fatty acids are formed from acetate and malonate. Thus, the biosynthesis of the fats involves the incorporation of certain intermediates of biological oxidation. Conversely, intermediates of biological oxidation are furnished when they are degraded—provided one ignores a-oxidation of fatty acids. 

HisN03,(CH3)3N + -CH2 CH0H CH2C00-. Isolated from skeletal muscle. It acts as a carrier for ethanoyl groups and fatty acyl groups across the mitochondrial membrane during the biosynthesis or oxidation of fatty acids. 

Glyoxylate cycle A modification of the Krebs cycle, which occurs in some bacteria. Acetyl coenzyme A is generated directly from oxidation of fatty acids or other lipid compounds. 

The TCA cycle can now be completed by converting succinate to oxaloacetate. This latter process represents a net oxidation. The TCA cycle breaks it down into (consecutively) an oxidation step, a hydration reaction, and a second oxidation step. The oxidation steps are accompanied by the reduction of an [FAD] and an NAD. The reduced coenzymes, [FADHg] and NADH, subsequently provide reducing power in the electron transport chain. (We see in Chapter 24 that virtually the same chemical strategy is used in /3-oxidation of fatty acids.)... 

Finally, citrate can be exported from the mitochondria and then broken down by ATP-citrate lyase to yield oxaloacetate and acetyl-CoA, a precursor of fatty acids (Figure 20.23). Oxaloacetate produced in this reaction is rapidly reduced to malate, which can then be processed in either of two ways it may be transported into mitochondria, where it is reoxidized to oxaloacetate, or it may be oxidatively decarboxylated to pyruvate by malic enzyme, with subse-... 

FIGURE 25.12 Elongation of fatty acids in mitochondria is initiated by the thiolase reaction. The /3-ketoacyl intermediate thus formed undergoes the same three reactions (in reverse order) that are the basis of /3-oxidation of fatty acids. Reduction of the /3-keto group is followed by dehydration to form a double bond. Reduction of the double bond yields a fatty acyl-CoA that is elongated by two carbons. Note that the reducing coenzyme for the second step is NADH, whereas the reductant for the fourth step is NADPH. 

The catalytic oxidation of long-chain paraffins (C18-C30) over manganese salts produces a mixture of fatty acids with different chain lengths. Temperature and pressure ranges of 105-120°C and 15-60 atmospheres are used. About 60 wt% yield of fatty acids in the range of C12-C14 is obtained. These acids are used for making soaps. The main source for fatty acids for soap manufacture, however, is the hydrolysis of fats and oils (a nonpetroleum source). Oxidation of paraffins to fatty acids may be illustrated as ... 

The onward metabohsm of succinate, leading to the regeneration of oxaloacetate, is the same sequence of chemical reactions as occurs in the P-oxidation of fatty acids dehydrogenation to form a carbon-carbon double bond, addition of water to form a hydroxyl group, and a hirther dehydrogenation to yield the oxo- group of oxaloacetate. 

Oxidation of Fatty Acids Produces a Large Quantity of ATP... 

Two major types of muscle fibers are found in humans white (anaerobic) and red (aerobic). The former are particularly used in sprints and the latter in prolonged aerobic exercise. During a sprint, muscle uses creatine phosphate and glycolysis as energy sources in the marathon, oxidation of fatty acids is of major importance during the later phases. Nonmuscle cells perform various types of mechanical work carried out by the structures constituting the cytoskeleton. These strucmres include actin filaments (microfilaments), micrombules (composed primarily of a- mbulin and p-mbulin), and intermediate filaments. The latter include keratins, vimentin-like proteins, neurofilaments, and lamins. 

The mechanisms of the metabolism and excretion of P-carotene are not clear, other than the identification of a number of partially oxidised intermediates found in plasma (Khachik et al., 1992). It is assumed that the carotenoids are metabolised in a manner analogous to the P-oxidation of fatty acids although there is no evidence for this. 

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