Nicotinamide adenine dinucleotide pentose phosphate pathway

The plant can also use the pentose phosphate pathway to break down glucose, but the main purpose of this pathway is the generation of reducing power in the form of NADPH (nicotinamide adenine dinucleotide... 

Niacin is a water-soluble vitamin. The RDA of niacin for the adult man is 19 mg. Niacin is converted in the bi>dy to the cofactor nicotinamide adenine dinucleotide (NAD). NAD also exists in a phosphorylated form, NADP The phosphate group occurs on the 2-hydrr>xyl group of the AMP half of the coenzyme, NAD and NADP are used in the catalysis of oxidation and reduction reactions. These reactions are called redox reactions. NAD cycles between the oxidized form, NAD, and the reduced form, NADH + H. The coenzyme functions to accept and donate electrons. NADP behaves in a similar fashion. It occurs as NADP and NADPH + HT The utilization of NAD is illustrated in the sections on glycolysis, the malatc-aspartate shuttle, ketone body metabolism, and fatty acid oxidation. The utilization of NADP is illustrated in the sectirrns concerning fatty acid synthesis and the pentose phosphate pathway. 

Figure 21 -8 Major glycolytic pathways of the erythrocyte. Substrates are in uppercase type, and enzymes are in parentheses. EMP, The Embden-Meyerhof pathway HMP hexose monophosphate pathway or pentose shunt RLC, the Rapoport-Luebering cycle ADP, adenosine diphosphate ATP, adenosine triphosphate NAD, nicotinamide-adenine dinudeotide NADH, reduced nicotinamide-adenine dinucleotide NADP, nicotinamide-adenine dinucleotide phosphate NADPH, reduced nicotinamide-adenine dinucleotide phosphate.The step from ribulose-5-phosphate, which is shown as being catalyzed by transketolase and transaldolase, is an abbreviation of this portion of the HMR...

Various inborn errors of metabolism (Table 25-1) result from deficiencies or absence of some of the enzymes listed in Figure 25-9. Some of these are discussed later in the chapter. The relationship of carbohydrate metabolism to the production of lactate, ketone bodies, and triglycerides is also depicted in Figure 25-9. The pentose phosphate pathway, also known as the hexose monophosphate shunt, is an alternative pathway for glucose metaboUsm that generates the reduced form of nicotinamide-adenine dinucleotide phosphate (NADPH), which is used in maintaining the integrity of red blood cell membranes, in lipid and steroid biosynthesis, in hydroxylation reactions, and in other anabolic reactions. The complete picture of intermediary metabolism of carbohydrates is rather complex and interwoven with the metabolism of lipids and amino acids. For details, readers should consult a biochemistry textbook. 

Transketolase is a TPP-dependent enzyme found in the cytosol of many tissues, especially hver and blood cells, in which principal carbohydrate pathways exist. In the pentose phosphate pathway, which additionally supplies reduced nicotinamide-adenine dinucleotide phosphate (NADPH) necessary for biosynthetic reactions, this enzyme catalyzes the reversible transfer of a glycoaldehyde moiety from the first two carbons of a donor ketose phosphate to the aldehyde carbon of an aldose phosphate. 

The pentose phosphate pathway (PPP) is the major pathway for recycling nicotinamide adenine dinucleotide (NAD) to nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) and for the production of ribose-5-phosphate that is needed for the synthesis of nucleotides. The function of the PPP depends on the synthesis of nicotinamide-adenine dinucleotide phosphate (NADP) and thiamin pyrophosphate, a coenzyme... 

Nicotinamide functions in the animal body as the active group of two important coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP).These coenzymes are involved in the mechanism of hydrogen transfer in living cells (see Chapter 9) NAD is involved in the oxidative phosphorylation system, the tricyclic acid (TCA) cycle and the metabolism of many molecules, including pyruvate, acetate, (3-hydroxy-butyrate, glycerol, fatty acids and glutamate NADPH is the hydrogen acceptor in the pentose phosphate pathway. 

The erythrocyte transketolase (ETK) activation assay (also known as the saturation test) measures the functional capacity of the enzyme transketolase in red blood cells i.e. erythrocytes). Transketolase is a thiamine-dependent enzyme in the non-oxidative branch of the pentose phosphate pathway (PPP), a process of glucose turnover that produces nicotinamide adenine dinucleotide phosphates (NADPH) as reducing equivalents and pentose sugars as essential components of nucleotides. In the absence of adequate thiamine, the PPP output is compromised. 

The pentose phosphate pathway is also known as the hexose monophosphate shunt and the phos-phogluconate pathway because of the variety of intermediates formed by the pathway under different conditons. The pathway which occurs in a wide variety of organisms including animals, plants and microorganisms is classihable as secondary metabolism (Section 10.5) due to the relatively small quantity of glucose catabolized by this route. In mammalian tissues, the pathway yields a number of important products, in particular, reduced nicotinamide adenine dinucleotide phosphate (NADPH) and pentose sugars. 

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