NADH

Luminescence has been used in conjunction with flow cells to detect electro-generated intennediates downstream of the electrode. The teclmique lends itself especially to the investigation of photoelectrochemical processes, since it can yield mfonnation about excited states of reactive species and their lifetimes. It has become an attractive detection method for various organic and inorganic compounds, and highly sensitive assays for several clinically important analytes such as oxalate, NADH, amino acids and various aliphatic and cyclic amines have been developed. It has also found use in microelectrode fundamental studies in low-dielectric-constant organic solvents. 

The reverse reaction also occurs m living systems NADH reduces acetaldehyde to ethanol m the presence of alcohol dehydrogenase In this process NADH serves as a hydride donor and is oxidized to NAD" while acetaldehyde is reduced... 

The NAD -NADH coenzyme system is involved m a large number of biological changes during the enzyme... 

Many naturally occurring substances are epoxides You have seen two examples of such compounds already m disparlure the sex attractant of the gypsy moth (Section 6 18) and m the carcinogenic epoxydiol formed from benzo[a]pyrene (Section 118) In most cases epoxides are biosynthesized by the enzyme catalyzed transfer of one of the oxy gen atoms of an O2 molecule to an alkene Because only one of the atoms of O2 is trans ferred to the substrate the enzymes that catalyze such transfers are classified as monooxy genases A biological reducing agent usually the coenzyme NADH (Section 15 11) is required as well... 

Enzyme catalyzed reductions of carbonyl groups are more often than not com pletely stereoselective Pyruvic acid for example is converted exclusively to (5) (+) lactic acid by the lactate dehydrogenase NADH system (Section 15 11) The enantiomer... 

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)... 

NADH is the reduced form of nicotinamide adenine dinucleotide. 

Insects poisoned with rotenone exhibit a steady decline ia oxygen consumption and the iasecticide has been shown to have a specific action ia interfering with the electron transport iavolved ia the oxidation of reduced nicotinamide adenine dinucleotide (NADH) to nicotinamide adenine dinucleotide (NAD) by cytochrome b. Poisoning, therefore, inhibits the mitochondrial oxidation of Krebs-cycle iatermediates which is catalysed by NAD. 

Glucose [50-99-7] urea [57-13-6] (qv), and cholesterol [57-88-5] (see Steroids) are the substrates most frequentiy measured, although there are many more substrates or metaboUtes that are determined in clinical laboratories using enzymes. Co-enzymes such as adenosine triphosphate [56-65-5] (ATP) and nicotinamide adenine dinucleotide [53-84-9] in its oxidized (NAD" ) or reduced (NADH) [58-68-4] form can be considered substrates. Enzymatic analysis is covered in detail elsewhere (9). 

Indicators There are certain compounds that are suitable as indicators for sensitive and specific clinical analysis. Nicotinamide adenine dinucleotide (NAD) occurs in oxidized (NAD" ) and reduced (NADH) forms. Nicotinamide adenine dinucleotide phosphate (NADP) also has two states, NADP" and NADPH. NADH has a very high uv—vis absorption at 339 nm, extinction coefficient = 6300 (M cm) , but NAD" does not. Similarly, NADPH absorbs light very strongly whereas NADP" does not. 

Two or more linked enzyme reactions can lead to a change in the concentration of NADH or NADPH that is equivalent to the concentration of the original analyte. The reference glucose measurement using hexokinase [9001-51-8] and glucose-6-phosphate dehydrogenase [9001-40-5] is an example ... 

Cltra.te The citrate reaction is followed by monitoring the decrease in the concentration of NADH. Oxaloacetate instantiy decarboxylates to pymvate. 

The loss of NADH is followed for determination of the en2yme creatine kinase. 

Laetate The formation of NADH is followed by measuring the absorbance at 340 nm. 

Enzymes, measured in clinical laboratories, for which kits are available include y-glutamyl transferase (GGT), alanine transferase [9000-86-6] (ALT), aldolase, a-amylase [9000-90-2] aspartate aminotransferase [9000-97-9], creatine kinase and its isoenzymes, galactose-l-phosphate uridyl transferase, Hpase, malate dehydrogenase [9001 -64-3], 5 -nucleotidase, phosphohexose isomerase, and pymvate kinase [9001-59-6]. One example is the measurement of aspartate aminotransferase, where the reaction is followed by monitoring the loss of NADH ... 

CH3)2CHCH2C0C00H + NH3 + NADH leucme dehydrogenase (CH3)2CHCH2CH NH2)COOH + NAD... 

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