Nicotinamide adenine dinucleotide biological function

Niacin is also known as vitamin PP or vitamin Bj. The term niacin describes two related compounds, nicotinic acid and nicotinamide (Figure 19.18), both with biological activity. Niacin is formed from the metabolism of tryptophan, and therefore it is not strictly a vitamin. It is a precursor of two cofactors nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are essential for the functioning of a wide range of enzymes involved in redox reactions. 

In addition to their role in the formation of DNA and RNA (see Section 27.2), nucleotides have other important biological functions. For example, adenosine triphosphate (ATP) is an important energy carrier in biochemical reactions, and nicotinamide adenine dinucleotide is a coenzyme that is often involved in biochemical oxidation-reduction reactions. 

In addition to enzymes, biological oxidations require substances known as coenzymes. Coenzymes are organic molecules that, in concert with an enzyme, act on a substrate to bring about chemical change. Most of the substances that we call vitamins are coenzymes. The coenzyme contains a functional group that is complementary to a functional group of the substrate the enzyme catalyzes the interaction of these mutually complementary functional groups. If ethanol is oxidized, some other substance must be reduced. This other substance is the oxidized form of the coenzyme nicotinamide adenine dinucleotide (NAD). Chemists and biochemists abbreviate the oxidized form of this... 

Enzymatic reactions, mechanisms, structures, and biological functions of nicotinamide adenine dinucleotide 07OBC2541. 

The covalent modification of proteins has been demonstrated to be an important and general in vivo mechanism for metabolic regulation (1). More recently it has been shown that nicotinamide adenine dinucleotide (NAD) can participate in such reactions as a donor of the adenosine diphosphate ribose (ADP-ribose) moiety (2, 3). Although the biological function of these reactions is still unknown, evidence has begun to accumulate suggesting that this class of modification constitutes an important regulatory mechanism. 

In considering biological oxidation reactions it is necessary first of all to outline the structure and function of nicotinamide adenine dinucleotide (NAD) which is the major coenzyme involved in such reactions. 

Fluorescence applications are ranging from in vivo and in vitro diagnostics to experimental biology. In the first case mainly intrinsic fluorescence is used, which arises from proteins (in particular the amino acid tryptophan [4,5]), extracellular fibres [6,7] or specific coenzymes, e.g. nicotinamide adenine dinucleotide (NADH). So far, fluorescence intensity of NADH has been correlated with metabolic functions [8,9] and was proposed to be an appropriate parameter for detection of ischemic [10,11] or neoplastic [12-14] tissues. The application of fluorescent probes for diagnostic purposes in humans has so far been limited to fluorescein or indocyanine green used... 

FIGURE 8 The nicotinamide-containing coenzymes nicotinamide-adenine dinucleotide (NAD) and nicotinamide-adenine dinucieotide phosphate (NADP). Aiso iiiustrated are their biological functions as hydrogen carriers. The nicotinamide ring accepts a hydride ion (H ) transferred directly from a subsfrate molecule. 

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