Nicotinamide adenine dinucleotide

• Nicotinamide adenine dinucleotide
• Nadid ( INN) (oxidized form, inner salt )

• C21H27N7O14P2 (oxidized form, inner salt )
• C21H29N7O14P2 (reduced form )

Colorless, hygroscopic powder (oxidized form, inner salt )

• 663.43 g · mol -1 (oxidized form, inner salt )
• 665.45 g · mol -1 ( reduced form)

Fixed

140-142 ° C ( decomposition) (oxidized form, inner salt )

Poorly in water (10 g · l -1)

Template: Infobox chemical / molecular formula search available

Nicotinamide adenine dinucleotide, actually nicotinamide adenine dinucleotide ( NAD abbreviated ) is a coenzyme that formally transfers a hydride ion ( Zwei-Elektronen/Ein-Proton ). It is involved in numerous oxidation-reduction reactions of the metabolism of the cell.

From the IUPAC / IUBMB abbreviations are proposed for the oxidized form NAD , NADH for the reduced form and NAD in general. Sometimes one finds, however, still held NAD NAD and NADH instead of NADH2.

The coenzyme was established in 1906 by Arthur Harden and William Young discovered ( Harden and Young ester). NAD was DPN in the older scientific literature also referred Diphosphopyridinnucleotid abbreviated until the early 1960's, or the name Codehydrase Codehydrogenase I or I or coenzyme I known.

Compared with the nicotinamide adenine dinucleotide phosphate ( NADP ) and Nicotinsäureadenindinukleotidphosphat ( NAADP ), two otherwise almost identically structured coenzymes, NAD has a phosphate residue at the adenosine less, NADP has on 2'C atom of the ribose phosphate moiety another.

Chemistry

Redox reaction of the NAD NAD , by addition of two electrons ( e-) and a proton (H ) to NADH can be reduced.

Biochemistry

Function

NAD is usually the organism as the oxidant. Therefore, the ratio of NADH / NAD small ( << 1 ) in order to achieve a correspondingly positive redox potential. As a reducing agent but is mainly NADPH used. Therefore, the ratio of NADPH / NADP large ( >> 1 ) in order to arrive at a corresponding negative redox potential. Therefore, there are two differentiable cofactors for the two redox reactions. A single redox couple could not simultaneously provide a high redox potential for biological oxidation and a low redox potential for biological reductions.

The high-energy, reduced form NADH is used in oxidative metabolism as an energy coenzyme of the respiratory chain, where ATP is generated. In their oxidation, they are previously recorded in the catabolic glucose and / or lipid metabolism electrons again and transmits it as oxygen. It eventually emerge NAD and water.

NAD is a coenzyme of dehydrogenases such as alcohol dehydrogenase (ADH), the oxidation of alcohol.

Biosynthesis

NAD is produced tryptophan in the body of both nicotinic acid ( niacin, vitamin B3) or nicotinamide, and from the degradation products of the amino acid. Since both starting materials are essential deficiency as pellagra are possible, but because of the two possible metabolic pathways in Europe rather rare.

Intersection of both reaction pathways is nicotinate D -ribonucleotide, which can be formed directly from nicotinic acid by using the nicotinate phosphoribosyltransferase, or arising from the tryptophan metabolite quinolinic acid by the enzyme quinolinate phosphoribosyltransferase. The latter reaction takes place mainly in the liver. For nicotinate D -ribonucleotide adenosine phosphate is added in the next step. This reaction is catalyzed by the Nicotinamidnukleotid adenylyltransferase, and there is Deamido - NAD . This will eventually aminated using the NAD synthase to NAD .

Another synthetic route begins with nicotinamide, which is reacted with the nicotinamide phosphoribosyltransferase to the dinucleotide; this is an amide, so that only the transfer of adenosine phosphate with the above-mentioned transferase is necessary to maintain NAD .

The high-energy, reduced form NADH produced in the catabolism ( glycolysis and the citric acid cycle in ).

Absorption properties

Nicotinamide adenine dinucleotide has both in its reduced (NADH ) and in its oxidized (NAD ) form on an identical Adeninbereich (see structural formula ). This absorbs light at a wavelength of 260 nm, which explains the one shown in the diagram, common absorption maximum in the 260 nm range is striking here is that at the same concentration of the substances the absorption of NAD in this area is higher than NADH. The reason for this is that the absorption of the oxidized, mesomeric Nicotinamidrings that also absorb at 260 nm superimposed on the absorbance of the adenine and so for the increased absorbance at 260 nm provides. Is of reduced nicotinamide, then a quinoid system which is now absorbed light having a wavelength of 340 nm.

This difference between the NAD and NADH in the UV spectrum makes it possible to observe the conversion between oxidized and reduced form of the coenzyme in a spectrophotometer. Thus, in a photometric enzyme assay, the oxidation and reduction of NAD or NADH can be observed when the enzyme used NAD is used as the substrate. The amount of this unreacted substrate can be monitored spectrophotometrically by the change in absorbance at 340 nm, the concentration can then be determined using the Lambert- Beer's law. Since this is proportional to the amount of unreacted co-substrate, and quantitative information about the amount of reacted substrate or product produced are thus indirectly possible. If one were to follow the substrate and product concentration directly, this would only be possible, however, much more difficult.