NADPH coenzyme

Step 2 The ketone carbonyl of the acetoacetyl group is reduced to an alcohol function This reduction requires NADPH as a coenzyme (NADPH is the phosphate ester of NADH and reacts similarly to it)... 

Very low concentrations of substrates may be assayed by recycling the test substrate for an appreciable but definite period of time and measuring the amount of product formed. The coenzyme NADPH, for instance, may be assayed using the two enzymes glutamate dehydrogenase (EC 1.4.1.3) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) ... 

Thus a constant supply of the reduced coenzyme (NADPH) is required, hence the importance of the pentose phosphate pathway (PPP) as described in Section 5.3.1.6. 

The reduced coenzyme NADPH is required for the reduction reactions shown in Figure 11.5. It is also required for elongation and desaturation of fatty acids. The major source of NADPH for these reactions is the pentose phosphate pathway, which is described in detail in Chapter 6. 

O2). One of the two oxygen atoms is transferred to the substrate, while the other is released as a water molecule. The necessary reducing equivalents are transferred to the actual monooxygenase by an FAD-containing auxiliary enzyme from the coenzyme NADPH+HT... 

FMN was first identified as the coenzyme of an enzyme system that catalyzes the oxidation of the reduced nicotinamide coenzyme, NADPH (reduced NADP), to NADP (nicotinamide adenine dinucleotide phosphate). NADP is an essential coenzyme for glucose-6-phosphate dehydrogenase which catalyzes the oxidation of glucose-6-phosphate to 6-phosphogluconrc acid. This reaction initiates the metabolism of glucose by a pathway other than the TCA cycle (citric acid cycle). The alternative route is known as the phosphoglneonate oxidative pathway, or the hexose monophosphate shunt. The first step is ... 

Comparison between synthesis and degradation of fatty acids in the liver. Both processes involve two carbons at a time and very similar intermediates, even though they go in opposite directions. CoA is also heavily involved in both processes. Here the similarities end. The enzymes used in the two processes are totally different, and the coenzymes are also different. In the degradative direction FAD and NAD+ are used, whereas in the synthetic direction the coenzyme NADPH is used. Degradation occurs in the mitochondrial matrix, and synthesis occurs in the cytosol. 

It has been established that the enzymic cleavage of Maillard-type compounds depends on the concentration of cytochrome P-450 and of the coenzyme NADPH (j3) (Fig. 3). The mechanism suggested for the enzymic cleavage of deoxyfructoserotonin is shown in Figure 4. Therefore, factors interfering with this enzyme system may prevent the detrimental effects of the Maillard reaction in diabetes. 

Some mammalian cells have the ability to metabolize glucose 6-phosphate in a pathway that involves the production of C3, C4, C5, C6, and C7 sugars. This process also yields the reduced coenzyme, NADPH, which is oxidized in the biosynthesis of fatty acids and steroids (Chap. 13). Consequently, this metabolic pathway is of major importance in those cells involved in fatty acid and steroid production, such as the liver, lactating mammary gland, adrenal cortex, and adipose tissue. The pentose phosphate pathway, which does not require oxygen and which occurs in the cytoplasm of these cells, has two other names the phosphogluconate pathway (after the first product in the pathway) and the hexose monophosphate shunt (since the end products of the pathway can reenter glycolysis). 

Fig. 7 Xylose reductase catalyzed xylitol synthesis. The coenzyme NADPH was regenerated by a NADP+-accepting mutant of phosphite dehydrogenase...

NADPH), which is similar to the coenzymes, NAD" and NADH, mentioned above, but with an additional phosphate attached to the 2-position of the ribose unit. SeeO Fig. 4 for the structures of these coenzymes. NADPH is responsible for reducing the carbon-carbon bond that is formed in fixing C02in photosynthesis. 

Die Entgiftungsreaktion ist eine Oxidationsreaktion, bei der das Cyanid in Gegenwart von Hydrogensulfid zum Thiocyanat-Ion (Summenformel SCIST) oxidiert wird. Als Oxidations-mittel kommt molekularer Sauerstoff in Anwesenheit des Coenzyms NADPH/H in Betracht. Dabei wird NADPH unter Abgabe von zwei Elektronen zu NADP co-oxidiert auBerdem entsteht Wasser. 

DHFR catalyzes the reduction of 7,8-dihydrofolate (DHF) to 5,6,7,8-tetrahydrofo-late (THF) through the oxidation of the coenzyme NADPH. DHFR has been studied extensively due to its role in maintaining intracellular pools of THF, which is an important component of several metabolic pathways. The reaction catalyzed by DHFR is thought to involve transfer of a proton followed by a hydride to DHF. 

The main chemical aspect in which compounds with a nitrogen in a five- or six-membered ring differ from their acyclic counterparts is that they can be dehydrogenated to the corresponding aromatic system. Dihydro-aromatic systems naturally show Ihe greatest tendency to aromatise, indeed one of the important reducing coenzymes, NADPH (a 1,4-dihydropyridine), makes use of this tendency - it is a hydride donor ... 

The basis of the catalysis of the splitting of the disulfide is presumably the formation of a charge-transfer complex between the two-electron donor NADPH (equivalent to a hydride anion) and the acceptor flavin combined with proximity effects. Both coenzymes, NADPH and FAD, are bound to the protein by adenosine phosphate-protein interactions, the substrate is loosely bound at the cleft between the units of a protein dimer (Fig. 9.6.12) (Schulz, 1983 Douglas, 1987). 

Reactions catalyzed by CYPs require several elements and generally, although not always, result in oxygenated metabolites. Successful in vitro reactions using microsomal tissues require NADPH and oxygen as essential cofactors. Purified CYP isoforms require a source of lipid, such as phosphatidylcholine, and the ncccs.sary coenzyme NADPH cytochrome P450 reductase. In some cases, other microsomal components, such a.s cytochrome bs, may also be required for optimal metabolic activity. 

Functional Stability of Microsomes. The coenzyme NADPH is required by yS mixed-function oxidases. Unfortunately the yS contain other enzymes that will oxidase NADPH or destroy it and adversely affect drug detoxification. The most Important among these are NAD(P)ase, NAD(P)H pyrophosphatase, and NAD(P)H oxidase. We added the competitive inhibitors sodium pyrophosphate and nicotinamide to reaction mixtures to block the effects of NAD(P)H pyrophosphatase and NAD(P)ase, respectively (10, 11). 

X-ray diffraction analysis of dihydrofolate reductase (DHFR), co-crystal-lized with methotrexate, has shed much light on the action of this inhibitor. This work, one of the earliest visualizations of a drug interacting with its receptor (Matthews etal., 1977), has since been refined to the remarkably clear resolution of 1.7 A (Bolin et al., 1982). A typical diagram of DHFR, its coenzyme (NADPH), and methotrexate is shown in Fig. 9.4. The enzyme depicted there is from Lactobacillus casei and the same authors also report on DHFR (with cocrystallized methotrexate) from the bacterium E. colt. However, they have not been able to co-crystallize methotrexate with DHFR from any vertebrate source. 

The coenzyme, NADPH, is fully extended the nicotinamide portion lies close against the pteridine ring in a position that would facilitate delivery of a hydride anion from the pyridine to the pteridine ring at C-6 (Filman et al., 1982). 

The cytochrome P450 (GYP) family of enzymes are the major catalysts that are responsible for a variety of oxidation reactions associated with the biotransformation of many xenobiotics that can be used to illustrate several concepts of toxication and detoxication in a chemistry course. The main function of this group of isozymes is to insert one atom of oxygen into a substrate thereby increasing hydrophilicity or water solubility. These enzymes are haem-containing proteins containing a reduced iron species essential for transferring electrons and work in concert with coenzymes NADPH and NADPH reductase. 

The second, so-called indicator reaction, provides the specificity of the method, since hexokinase also converts other hexoses, such as D-fructose and D-mannose, into their phosphorylated compounds. The formation of the coenzyme NADPH (the reduced form of nicotinamide adenine dinucleotide phosphate) can be measured photometrically, preferably at the absorption band maximum at 340 nm (see Figure 2). The hexokinase method has been internationally recommended as a reference method. 

The Hantzsch ester, 3,5-bis(ethoxycarbonyl)l,4-dihydro-2,6-dimethylpyr-idine, 3, can be made to mimic the behaviour of coenzyme NADPH by the addition of silica gel which acts as an acid catalyst [117]. 

Type I fatty acid synthase. Enzyme activities are arrtmged as a series of globular domains in a single multifunctional protein, 4-5 x 10, consisting of two identical subunits, each of M, 1.8-2.5 x lO , i. e. oj structure. P-Ketoacyl synthase activity is only present in the dimer, since this activity requires juxtaposition of two thiols, one from each subunit. The enoyl reductase does not use a flavin coenzyme (NADPH is used directly for the reduction). Termination is by hydrolysis (thioesterase), and the products are chiefly palmitate with some stearate. 

Both reduced coenzymes, NADPH and NADH, control hydrogenation, NADPH being more important. An interesting review on biochemistry and biosynthesis of these agents has been recently published (Chaykin, 1967). 

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