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Niacinamide (nicotinamide)

Niacinamide (also known as nicotinamide and 3-pyridine carboxamide) and nicotinic acid (also known as niacin and 3-pyridine carboxylic acid), both commonly referred to as vitamin B3, are members of the B-vitamin complex and precursors of coenzymes I and II. These compounds are important supplements to the diet of humans and animals. A coenzyme, sometimes referred to as a cofactor, is a thermostable nonprotein compound of relatively low molecular weight which is essential for the catalytic action of many enzymes. Enzymes are biological catalysts capable of initiating, promoting, and governing chemical reactions. Typically, an enzyme reacts with one or more substrates to produce products without being used up in the process or becoming a part of the products formed. In many enzymatic reactions, the presence of an active coenzyme is required. Examples of well known coenzymes are nicotinamide-adenine-dinucleotide (NAD), nicotinamide adenine dinucleotide phosphate (NADP), flavin-adenine-dinucleotide (FAD), and adenosine-triphosphate (ATP). Nicotinamide Adenine Dinucleotide (NAD) is a cofactor which is useful in a variety of enzyme catalyzed reactions, such as producing optically active alcohols, synthesizing carbohydrates, synthesizing fine chemicals, producing aldehydes and carboxylic acids, functionalizing hydrocarbons, and producing amino acids. Nicotinamide and its metabolic equivalent nicotinic acid (niacin, vitamin B3) or even tryptophane which is the synthetic precursor to niacin is the main precursor for the formation and maintenance of the cellular pool of NAD. NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate) are enzyme cofactors which are widely used in the measurement of enzyme activities and metabolites. They are also substrates for NAD(P)ases which catalytically break down these products into nicotinamide and ADP-ribose or ADP-ribose phosphate. In addition, NAD is also a substrate for poly (ADP-ribose) polymerase and mono (ADP-ribose) transferases important in DNA repair, apoptosis, differentiation and signal transduction. Niacin reacts with PRPP to form niacin mononucleotide (dNAM) The enzyme catalyzing this reaction is niacin phosphoribosyl transferase and is widely distributed in various tissues. Both pathways starting either from tryptophan or from niacin as NAD precursors merge at the stage of the niacin mononucleotide formalin. Niacinamide reacts with PRPP to give niacinamide mononucleotide (NAM). The enzyme that catalyses this reaction is niacinamide phosphoribosyl transferase. This enzyme is specific for niacinamide and is entirely distinct from niacin phosphoribosyl transferase. It is also widely distributed in various tissues.

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