Muscle oxidation

B. Faraut, B. Giannesini, V. Matarazzo, Y. Le Fur, G. Rougon, P. J. Cozzone and D. Behdahan, Capsiate administration results in an uncoupling protein-3 downregula-tion, an enhanced muscle oxidative capacity and a decreased abdominal fat content in vivo. Int. J. Obes. (Lond), 2009, 339,1348-1355. 

Gollnlck, P. D. and Saltln, B. (1982) Significance of skeletal muscle oxidative enzyme enhancement with endurance training. Clin. Physiol. 2 1-12. 

Tissues such as muscle oxidize the fatty acids to C02 and H20. 

C. Skeletal muscle oxidizes ketone bodies, which are synthesized in the liver from fatty acids derived from adipose tissue. 

Acetoacetate and 6-hydroxybutyrate are products of normal metabolism of fatty acid oxidation and serve as metabolic fuels in extrahepatic tissues. Their level in blood depends on the rates of production and utilization. Oxidation increases as their plasma level increases. Some extra-hepatic tissues (e.g., muscle) oxidize them in preference to glucose and fatty acid. Normally, the serum concentration of ketone bodies is less than 0.3 mM/L. 

The efflux of amino acids from skeletal muscle supports the essential amino acid pool in the blood (see Fig. 42.3). Skeletal muscle oxidizes the BCAA (valine, leucine, isoleucine) to produce energy and glutamine. The amino groups of the BCAA, and of aspartate and glutamate, are transferred out of skeletal muscle in alanine and glutamine. Alanine and glutamine account for approximately 50% of the total a-amino nitrogen released by skeletal muscle (Fig. 42.4). 

Hypothyroidism may also impair substrate utifization. Hypothyroidism decreased the insulin-regulated rates of glucose uptake into muscle fibers, and glucose utilization within the muscle fiber to synthesize glycogen or metabolize in glycolysis (Dimitriadis et ai, 2006 Dubaniewicz et al, 1989). Furthermore, mitochondrial function is impaired in hypothyroid muscles, manifested by a decrease in the maximal mitochondrial respiratory rate (ZoU et al, 2001), reduced O2 consumption (Crespo-Armas et al, 1992) and reduced muscle oxidative capacity (Baldwin etal, 1980 Dudley et al, 1987 McAllister 1991). 

The lipids in lean beef consist of about 2 to 4% triacylglycerols and 0.8 to 1% phospholipids containing 44% polyunsaturated fatty acids, which are mainly subject to oxidation. Oxidation occurs initially in the phospholipids of ceUular and subcellular membranes, which are in close proximity to the heme catalysts of the mitochondria and microsomes. A typical fatty acid composition of beef membrane phospholipids includes 22% 18 2,2% 18 3,15% 20 4, less than 1% 20 5 and 2% 22 6. Phosphatidylethanolamine is the main phospholipid implicated in lipid oxidation of cooked meat. Chicken and turkey muscle are more susceptible to oxidation than beef, because of their higher polyunsaturated phospholipid fraction and relatively low levels of natural tocopherols. Red poultry muscles oxidize faster than white because of higher phospholipid and iron contents. 

Succinoxidase. Washed particles from heart muscle oxidize succinate to fumarate with oxygen as electron acceptor, This is the so-called succinoxidase preparation. The initial step in the oxidation of succinate has recently been found to be catalyzed by an iron-flavoprotein. When this is isolated from other components of succinoxidase, it fails to react with other enzymes and reduces efficiently only phenazines of the several oxidants that are effective with more complex preparations. Partially fragmented particles have been obtained by differential centrifugation of isobutanol-treated preparations of larger particles from mitochondria or by digestion with trypsin in the presence of cholate. These treatments yield preparations that can reduce cytochrome c. ... 

In adipose tissue glucose uptake is diminished and triglyceride breakdown is increased. The fatty acids produced are exported via the plasma and are oxidized by other tissues, while the glycerol is used for gluconeogenesis in the liver. Muscle oxidizes mainly fatty acids and ketone bodies while the brain adapts to use ketone bodies rather than glucose as a major energy source. This ability of the brain to use ketone bodies reduces the requirement for amino acids as a source of glucose, and is a factor of importance in the conservation of body protein. 

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