Vitamin B3 (Niacin)- help to prevent pellagra
Niacin is a water-souluble vitamin, also known as vitamin
B3. Niacin is the generic term for nicotinic acid (pyridine 3-carboxylic acid)
and nicotinamide (nicotinic acid amide) and the coenzyme forms of the vitamin.
Nicotinamide is the active form, which functions as a
constituent of two coenzymes, namely, nicotinamide adenine dinucleotide (NAD)
and nicotinamide adenine dinucleotide phosphate (NADP). In the forms of these
coenzymes, niacin functions in many biological redox reactions which activate
about 200 dehydrogenases essential to electron transport and other cellular
respiratory reactions. NAD functions as an electron carrier for intracellular
respiration as well as a co-factor for enzymes involved in the oxidation
(catabolism) of fats, proteins, carbohydrates and alcohol to produce energy.
NADP functions as a hydrogen donor in reductive biosynthesis (anabolism), such
as in fatty acid and steroid synthesis. Like NAD, NADP is a cofactor for
enzymes, such as in the oxidation of glucose-6-phosphate to ribose-5-phosphate
in the pentose phosphate pathway.
In non-redox reactions, NAD is the substrate for two
classes of enzymes that separate the niacin moiety from NAD and transfer
ADP-ribose to proteins. A third class of enzymes catalyses the formation of
cyclic ADP-ribose. This molecule also functions within cells to provoke the
release of calcium ions from internal storage sites and may also plays a role
in cell-signaling.
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