Important in Energy Metabolism

Thiamin is widespread in many nutritious foods but pig meat, liver, whole-grain cereals, legumes and nuts are particularly rich sources. Because of its importance in energy metabolism, the RDA for thiamin is quoted in terms of energy intake (0.12mgkJ 1 day-1 1 mg day-1 minimum). This is approximately equivalent to 1.5 mg and 1.1 mg per day for men and women, respectively. The RNI value for thiamin is 0.4 mg per 1000 kcal (4186 kJ) per day for adults. 

Most carbohydrates in nature exist as high-molecular-weight polymers called polysaccharides. Polysaccharides are composed of simple or derived sugars connected by gly-cosidic bonds. In this chapter we restrict ourselves to a description of homopolymers of glucose because they are the most important in energy metabolism. 

NAD and NADP, although very similar, have very different functions. NADH is very important in energy metabolism (e.g. Chapters 16 and 33) and catabolic pathways. NADPH is very important in anabolic pathways, e.g. fatty acid synthesis (Chapter 21) and the respiratory burst (Chapter 14). 

Water-Soluble Vitamins. Vitamin G (ascorbic acid) functions in the formation of collagen, wound healing, metabolic functions, and other roles. Foods high in vitamin G include citrus fruits, strawberries, cantaloupe, and cruciferous vegetables. B vitamins are important in energy metabolism. Thiamin (Bj) is called the antineuritic vitamin. Riboflavin (B ), rarely deficient in the diet, is found most abundantly in milk and dairy products. Niacin (Bj) is prevalent in meats, poultry, fish, peanut butter, and other foods. Other major B vitamins include folic acid (B ), B, and Bj2-... 

As a component of biotin, sulfur is important in fat metabolism as a component of thiamin and insulin, it is important in carbohydrate metabolism as a component of coenzyme A, it is important in energy metabolism as a component of certain complex carbohydrates, it is important in various connective tissues. Insulin and glutathione, regulators of energy metabolism, contain sulfur. Also, sulfur compounds combine with toxic substances such as phenols and cresols and convert them to a nontoxic form, following which they are excreted in the urine. 

Using the transport systems in the membranes, cells regulate their volume, internal pH value, and ionic environment. They concentrate metabolites that are important for energy metabolism and biosynthesis, and exclude toxic substances. Transport systems also serve to establish ion gradients, which are required for oxidative phosphorylation and stimulation of muscle and nerve cells, for example (see p. 350). 

The oxidative decarboxylation of pyruvate and a-ketoglutaraie I which plays a key role in energy metabolism of most cells, is parn ularly important in tissues of the nervous system. In thiaminel deficiency, the activity of these two dehydrogenase reactions <1 decreased, resulting in a decreased production of ATP and, fxsi I... 

Since oxidation processes are so important in the metabolism of aerobic organisms, it is often convenient to discuss Gibbs energies of combustion. These are easily derived from the Gibbs energies of formation. For example, AGC for acetate ion (aqueous) may be obtained as follows ... 

F atty acids, as components of phospholipids, are important structural elements of biological membranes and, like carbohydrates, are important sources of energy. In this chapter we focus on the role of fatty acids in energy metabolism. We see that fatty acids are both assembled and de-... 

These oxidation reactions employing pyridine nucleotides and flavoproteins are especially important in primary metabolism in liberating energy from fuel molecules in the form of ATP. The reduced coenzymes formed in the process are normally reoxidized via the electron transport chain... 

Another important difficulty in the evaluation of the correct activity values for enzymes involved in energy metabolism in neurons resides in the fact that opposite processes may occur simultaneously, like the reduction of neuronal metabolism and compensatory enhancement in glial activity. The altered activities of some glycolytic enzymes in brain homogenates represent a net-effect, and it is unclear how the energy state (ATP level) of the neurons is perturbed if the metabolic activation is... 

Copper plays an important role in the constituents of many enzymes of the mammalian organism as well as in plants and anthropods. Several classes of oxidizing enzymes for copper have been described, including the cytochrome oxidases which are the terminal oxidases in the mitochondrial electron transport system, a key reaction in energy metabolism (34), and the amine oxidases (35) of which there are a number that contain copper (36,37,38), Lysyl oxidase (39) is probably the most important since it plays a major role in elastin and collagen synthesis... 

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