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Nicotinamide Nucleotides

These comprises of coenzymes involved in hydrogen transfer reactions and form essential components of dehydrogenases taking part in fermentation and glycolysis. The coenzymes are known as nicotinamide adenine dinucleotide (NAD+), formerly known as coenzymes I isolated by H.von Euler in 1931, and nicotinamide and nicotinamide adenine dinucleotide phosphate (NADP+) also known as coenzyme II discovered by Warburg and Christian. Collectively these coenzymes are known as pyridine nucleotides.
Pyridine nucleotides are derived from vitamin B, nicotinic acid or niacin which is widely distributed in plant and animal tissues. The amide of nicotinic acid, called nocotinamide is the most active from present in attached to the ribose molecule through glycosidic linkage while the phosphate group provides a link between adenosine and nicotinamide riboside. In NADP, there is an additional phosphate group in C-2 position of the ribose molecule of adenosine component, hence it is called nicotinamide dinucleotide phosphate.
Biochemical function   The physiological functions and the behavior of these coenzymes as vitamins has been known for a long time. The pyridine ring of the coenzymes is positively charged and undergoes a change during oxidation reduction reactions the hydrogen can reversibly bind with the pyridine ring. The uptake of hydrogen causes reductions retaining two double bonds, accompanied by a loss of positive charge on the nitrogen.
These pyridine nucleotides, NAD+ and NADP and coenzymes of a number of dehydrogenases catalyzing oxidation reduction reactions. They have been sometimes called cosubstrates since the enzymes of which they form a prosthetic component are substrate specific. All reaction catalyzed by them are reversible.

nicotinamide nucleotides

In the above reaction, ethanol is oxidized to acetaldehyde by removal of two hydrogens that are picked up by NAD+ which is said to be reduced. The reaction induces a change in the aromatic nature of the pyridine ring altering the light absorbing quality of the molecule. The reduced form of NAD shows maximum absorption of UV light at 340 nm, while the oxidized form of NAD+ does not absorb at that wavelength the two coenzymes have different functions. NADH functions as a coenzyme in such reactions where the ultimate acceptor of hydrogen is molecular oxygen to form water. The transfer or hydrogen and electrons generate ATP through an electron transport mechanism. On the other hand NADP is used as a coenzyme in reactions where the hydrogens are transferred to an organic compound for biosynthesis.

dehydrogenase requiring nicotinamide nucleotide coenzyme

Nicotinic acid and derivative nicotinamide and component of NAD+

Nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate (NAD+) AND NADP+

Oxidized NAD or NADP and Reduced NADH or NADPH

UV absorption spectrum of reduced and oxidized form of NAD+

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