NAD oxidation

Reductive sequences involving flavoproteins may be represented as the reverse reaction, where hydride is transferred from the coenzyme, and a proton is obtained from the medium. The reaction mechanism shown here is in many ways similar to that in NAD+ oxidations, i.e. a combination of hydride and a proton (see Box 11.2) it is less easy to explain adequately why it occurs, and we do not consider any detailed explanation advantageous to our studies. We should register only that the reaction involves the N=C-C=N function that spans both rings of the pteridine system. 

NAD Oxidized nicotinamide adenine rRNA Ribosomal ribonucleic acid... 

IDE IF Intermediate density lipoprotein Initiation factor NAD+ Oxidized nicotinamide adenine dinucleotide... 

The alkaloids are also relevant to drug design. Alkaloids are complex heterocyclic compounds that contain nitrogen and thus have base-like (hence the term alkaloid ) properties they are extremely structurally diverse. Nicotine is one of the simplest alkaloids. Oxidation of nicotine produces nicotinic acid, a vitamin that is incorporated into the important coenzyme nicotinamide adenine dinucleotide, commonly referred to as NAD" (oxidized form). The neurotransmitter serotonin is an alkaloid containing the aromatic indole ring system. 

Ethylene glycol is used as a freezing-point depressant in automotive antifreeze. It is highly toxic because the enzyme alcohol dehydrogenase and the coenzyme nicotinamide adenine dinucleotide (NAD) oxidize ethylene glycol to much more liver-toxic compounds like glyoxal, hydroxyacetaldehyde, glyoxylic... 

Answer Dietary niacin is used to synthesize NAD+. Oxidations carried out by NAD+ are part of cyclic oxidation-reduction processes, with NAD+/NADH as an electron carrier. Because of this cycling, one molecule of NAD+ can oxidize many thousands of molecules of glucose, and thus the dietary requirement for the precursor vitamin (niacin) is relatively small. 

Answer TPP thiazolium ring adds to a carbon of pyruvate, then stabilizes the resulting car-banion by acting as an electron sink. Lipoic acid oxidizes pyruvate to level of acetate (acetyl-CoA), and activates acetate as a thioester. CoA-SH activates acetate as thioester. FAD oxidizes lipoic acid. NAD+ oxidizes FAD. (See Fig. 16-6.)... 

Step 1 Base deprotonates the C4 hydroxyl group while NAD+ oxidizes the alcohol to a ketone. 

Li(NAD + )-2H20,Li(C2iH26N70,4P2)-2H20 (NAD = oxidized form of nicotinamide adenine dinucleotide) (lithium is surrounded by a nitrogen and three oxygens provided by two different NAD molecules)... 

Figure 6. Proposed pyridine nucleotide cycle. Abbreviations NaMN, nicotinic acid mononucleotide NaAD, nicotinic acid adenine dinucleotide and NAD, oxidized form of nicotinamide adenine dinucleotide.

Nicotinic acid (niacin) Nicotinamide adenine dinucleotide (NAD+) Oxidation-reduction Pellagra (dermatitis, depression, diarrhea)... 

NAD+ Oxidized form of nicotinamide adenine dinucleotide. Note that despite the plus sign in the symbol, the coenzyme is anionic under normal physiological conditions. NAD+ is a coenzyme derived from the B vitamin niacin. It is transformed into NADH when it accepts a pair of high-energy electrons for transport in cells and is associated with catabolic and energy-yielding reactions. 

FMN, flavin mononucleotide GMP, guanosine monophosphate GTP, guanosine triphosphate NAD, nicotinamide-adenine dinucleotide (NAD+, oxidized form NADH, reduced form). 

The pig heart enzyme is very fast in the physiological direction (NAD to NADH) with a turnover number of 550 s at pH 7.6 and 25 °C. In the opposite direction (NADH to NAD ), NAD has an activating effect because excess NADH will over-reduce the enzyme to EH4, which is not competent for catalysis (Scheme 16). NAD" " oxidizes this dead-end complex, increasing the amount of EH2. The enzyme from E. coli is especially susceptible to inhibition from over-reduction by NADH because the redox potentials of EH2 and EH4 are closer than in enzymes from other sources. As a consequence of closer potentials, the EH2 state... 

Accurate estimates of all the kinetic coefficients in Eq. (1) or (2) are needed for the reaction in each direction, and at the same pH value, if reliable conclusions about mechanisms are to be reached. A sensitive method for measuring changes of reactant concentration is demanded because accurate estimates of v can only be made from progress curves that are linear for 30 sec or more, during which only a small fraction of the total reaction to equilibrium occurs. Moreover, Km values and dissociation constants of binary complexes of the coenzyme are often small (10 -10 M), and the equilibrium is usually unfavorable for NAD oxidation at pH 7.0 and in studies of product inhibition. Measurements of the fluorescence of the reduced coenzymes with a simple recording fluorometer provide a more sensitive analytical method than spectrophotometry 10,11). 

Nicotinamide (34) and structurally related 51 compounds were subjected to the halting activity bioassay to elucidate the structure-activity relationships [105]. The highest activity was recorded in thionicotinamide (35) followed by pyrazinamide (36) and nicotinamide (34). Nicotinamide adenine dinucleotide (NAD) (oxidized form), nicotinamide adenine dinucleotide phosphate (NADP) (oxidized form), (3-nicotinamide mononucleotide (oxidized form) showed halting activity at ca. 10"7 M... 

NAD oxidizes a compound by accepting a hydride ion from it. In this way, the number of carbon-hydrogen bonds in the compound decreases (the compound is oxidized) and the number of carbon-hydrogen bonds in NAD increases (NAD is reduced). NAD can accept a hydride ion at the 4-position of the pyridine ring because the electrons can be delocalized onto the positively charged nitrogen atom. Although NAD could also accept a hydride ion at the 2-position, the hydride ion is always delivered to the 4-position in enzyme-catalyzed reactions. 

NAD and NADH are the most common redox reagents in living systems. NAD oxidizes a compound by accepting a hydride ion from it NADH reduces a compound by donating a hydride ion to it. 

Nonenzyme-bound FAD is a stronger oxidizing agent than NAD. How, then, can NAD oxidize the reduced flavoenzyme in the pyruvate dehydrogenase system ... 

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