Oxidation-reduction reactions metabolic

Niacin was discovered as a nutrient during studies of pellagra. It is not strictly a vitamin since it can be synthesized in the body from the essential amino acid tryptophan. Two compounds, nicotinic acid and nicotinamide, have the biologic activity of niacin its metabolic function is as the nicotinamide ring of the coenzymes NAD and NADP in oxidation-reduction reactions (Figure 45-11). About 60 mg of tryptophan is equivalent to 1 mg of dietary niacin. The niacin content of foods is expressed as mg niacin equivalents = mg preformed niacin + 1/60 X mg tryptophan. Because most of the niacin in cereals is biologically unavailable, this is discounted. 

Metabolism of trimethylamine oxide in fish muscle involves an enzyme-catalyzed oxidation-reduction reaction. The enzyme responsible for the conversion of trimethylamine oxide to trimethylamine is known as trimethylamine-W-oxide reductase. This enzyme acts on nicotinamide adenine dinucleotide (NADH) and TMAO to produce NAD+, trimethylamine and water (Fig. 13.13.1). TMAO acts as the oxidizing agent and is reduced, while NADH undergoes oxidation as the reducing agent. 

Since many of the transformations undergone by metabolites involve changes in oxidation state, it is understandable that cofactors have been developed to act as electron acceptors/ donors. One of the most important is that based on NAD/NADP. NAD+ can accept what is essentially two electrons and a proton (a hydride ion) from a substrate such as ethanol in a reaction catalysed by alcohol dehydrogenase, to give the oxidized product, acetaldehyde and the reduced cofactor NADH plus a proton (Figure 5.2). Whereas redox reactions on metal centres usually involve only electron transfers, many oxidation/reduction reactions in intermediary metabolism, as in the case above, involve not only electron transfer but... 

The oxidation/reduction reactions that require one of the nicotinamide coenzymes are everywhere in metabolism in the glycolytic pathway, the citric acid cycle, the synthesis and degradation of fatty acids, the synthesis of steroids, and so on. Certain of... 

Nicotinic acid and nicotinamide are precursors of the coenzymes NAD+ and NADP+, which play a vital role in oxidation-reduction reactions (see Box 7.6), and are the most important electron carriers in intermediary metabolism (see Section 15.1.1). We shall look further at the chemistry of NAD+ and NADP+ shortly (see Box 11.2), but note that, in these compounds, nicotinamide is bound to the rest of the molecule as an A-pyridinium salt. 

Riboflavin (vitamin B2) is a component of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), coenzymes that play a major role in oxidation-reduction reactions (see Section 15.1.1). Many key enzymes involved in metabolic pathways are actually covalently bound to riboflavin, and are thus termed flavoproteins. 

Mechanism of Action Assists in collagen formation and tissue repair and is involved in oxidation reduction reactions and other metabolicreactions.TAerapeMficEffect Involved in carbohydrate use and metabolism, as well as synthesis of carnitine, lipids, and proteins. Preserves blood vessel integrity. 

Water is both the solvent in which metabolic reactions occur and a reactant in many biochemical processes, including hydrolysis, condensation, and oxidation-reduction reactions. 

The transfer of phosphoryl groups is a central feature of metabolism. Equally important is another kind of transfer, electron transfer in oxidation-reduction reactions. These reactions involve the loss of electrons by one chemical species, which is thereby oxidized, and the gain of electrons by another, which is reduced. The flow of electrons in oxidation-reduction reactions is responsible, directly or indirectly, for all work done by living organisms. In nonphotosynthetic organisms, the sources of electrons are reduced compounds (foods) in photosynthetic organisms, the initial electron donor is a chemical species excited by the absorption of light. The path of electron flow in metabolism is complex. Electrons move from various metabolic intermediates to specialized electron carriers in enzyme-catalyzed reactions. 

We live under a blanket of the powerful oxidant 02. By cell respiration oxygen is reduced to H20, which is a very poor reductant. Toward the other end of the scale of oxidizing strength lies the very weak oxidant H+, which some bacteria are able to convert to the strong reductant H2. The 02 -H20 and H+ - H2 couples define two biologically important oxidation-reduction (redox) systems. Lying between these two systems are a host of other pairs of metabolically important substances engaged in oxidation-reduction reactions within cells. 

COPPER (In Biological Systems), The activity of copper in plant metabolism manifests itself in two forms 11) synthesis of chlorophyll, and 12) activity of enzymes. In leaves, most of the copper occurs in close association with chlorophyll, but little is known of ns rale in chlorophyll synthesis, other than the presence of cupper is required. Copper is a definite constituent of several enzymes catalyzing oxidation-reduction reactions (oxidases), in which the activity is believed to be due to the shuttling of copper between the +1 and +2 oxidalicm states,... 

NADP Nicotinamide adenine dinucleotide phosphate NADP and the related NAD (the reduced forms are NADPH2 and NADH2) are coenzymes that are involved in diverse oxidation-reduction reactions in biologic systems among the processes that require NADPH2 is the metabolism of many toxicants by microsomal enzymes in the mammalian liver. 

Flavoproteins are involved in a large variety of key metabolic reactions in all forms of life. They catalvze over a potential span of several hundred millivolts oxidation-reduction reactions involving alkanes, alkenes, alco-... 

Oxidation-reduction reactions are among the most important in chemistry, biochemistry, and industry. Combustion of coal, natural gas, and gasoline for heat and power are redox reactions, as are the recovery of metals such as iron and aluminum from their oxide ores and the production of chemicals such as sulfuric acid from sulfur, air, and water. The human body metabolizes sugars through redox reactions to obtain energy the reaction products are liquid water and gaseous carbon dioxide. 

Monofunctional inducers share certain common chemical properties. They are electrophilic compounds that are capable of reacting with sulfhydryl groups in addition, certain compounds can also undergo oxidation-reduction reactions (28). The bifunctional inducers acquire these properties following oxidative metabolism. Compounds such as the isothiocyanates and diethyl maleate do not require metabolism and can directly react with sulfhydryl groups, oxidizing cysteine... 

Maintenance of water homeostasis is paramount to life for all organisms. In mammals, the maintenance of osmotic pressure and water distribution in the various body fluid compartments is primarily a function of the four major electrolytes, Na", K , Cl", and HCOi". In addition to water homeostasis, these electrolytes play an important role in the maintenance of pH, proper heart and muscle function, oxidation-reduction reactions, and as cofactors for enzymes. Indeed, there are almost no metabolic processes that are not dependent on or affected by electrolytes. Abnormal concentrations of electrolytes may be either the cause or the consequence of a variety of disorders. Thus determination of electrolytes is one of the most important functions of the clinical laboratory. Interpretation of abnormal osmolality and acid-base values requires specific knowledge of the electrolytes. Because of their physiological and clinical interrelationship, this chapter discusses determination. of electrolytes, osmolality, acid-base status, and blood oxygenation. 

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