Lipid metabolism energy yield

Nucleotides play important roles in all major aspects of metabolism. ATP, an adenine nucleotide, is the major substance used by all organisms for the transfer of chemical energy from energy-yielding reactions to energy-requiring reactions such as biosynthesis. Other nucleotides are activated intermediates in the synthesis of carbohydrates, lipids, proteins, and nucleic acids. Adenine nucleotides are components of many major coenzymes, such as NAD+, NADP+, FAD, and CoA. (See chapter 10 for structures of these coenzymes.)... 

In addition to being incorporated into tissue proteins, amino acids, after losing their nitrogen atoms by deamination and/or transamination, may be catabolized to yield energy or to form glucose. Conversely, the nonessential amino acids may be synthesized from carbohydrate metabolism intermediates and ammonia or from essential amino acids. This section is devoted to the mechanisms of such metabolic processes and their interrelationships with carbohydrate and lipid metabolic pathways. 

In pantothenic acid-deficient rats, tissue CoA is depleted, affecting mainly the peroxisomal oxidation of fatty acids, which is mainly concerned with detoxication mitochondrial /3 -oxidation, which is an essential energy-yielding pathway, is spared to a great extent (Youssef et al., 1997). However, relatively moderate deficiency in animals results in increased plasma triacylglycerol and nonesterifled fatty acids, suggesting some impairment of lipid metabolism (Wittwer et al., 1990). 

Carr, T.P and Cowles, R.L., Lipid supplements in exercise and sports, in Energy-Yielding Macronutrients and Energy Metabolism in Sport Nutrition, Driskell, J.A. and Wolinsky, I., Eds., CRC Press, Boca Raton, FL, 2000, pp. 183-189. 

Autotrophy A unique form of metabolism foimd only in bacteria. Inorganic compounds (e.g., NH3, N02-, S2, and Fe2+) are oxidized directly (without using sunlight) to yield energy. This metabolic mode also requires energy for C02 reduction, like photosynthesis, but no lipid-mediated processes are involved. This metabolic mode has also been called chemotrophy, chemoautotrophy, or chemolithotrophy. 

Upon oxidation in metabolism, lipids yield large amounts of energy. 

Aconitase (ACO) is a mitochondrial protein that acts as the second enzyme in the TCA cycle contributing to overall energy production. Aconitase activity is significantly reduced in the striatum and cortex of HD individuals thereby yielding in overall decrease of ATP production (Sorolla et al. 2008). Mitochondrial dysfunction, which is observed in HD, can occur via the oxidative modification of aconitase (Petrozzi et al. 2007). Decreased ATP production due to lipid peroxidation can lead to altered energy metabolism and reduced gluconeogenesis, which have been associated with HD pathogenesis (Josefsen et al. 2010). 

With the development of stable, energy dense, isotonic lipid emulsions for intravenous use (Table IV), the use of concentrated glucose solutions which have to be infused through large calibre central veins has decreased. Administration of nutrients by peripheral vein eliminates the complications associated with central catheter placement and use (Jako-bowski et al., 1979). Intravenous fat emulsions are manufactured from either soyabean or safflower oil, stabilized with 1.2% egg phospholipid, and made isotonic with 2.5% glycerol. Formulations are rich in essential fatty acids, yield 1.1 kcal/ml, and have a metabolic fate which is similar to that of naturally occurring chylomicrons. Liposyn, however, has only trace amounts of linolenic acid compared to the two other emulsions. In addition, carnitine is absent from all of the lipid emulsions. 

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