NUTR 3210 Lecture Notes - Lecture 11: Nicotinamide Adenine Dinucleotide Phosphate, Pentose Phosphate Pathway, Vitamin B3 Complex
1 May 2018
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NUTR3210 – Vitamins and Minerals III
*formation of eicosanoids on first slide is not necessary (second slide is)
Where do micronutrients fit in? see slide
Niacin (Vitamin B3) widely distributed in food (e.g. fish, meat, bread, cereal)
• Nicotinic acid (form found in plants; provitamin NAD and NADP)
o NAD+ and NADP+ act as coenzymes in over 400 different redox reactions in the body
o NAD+ = nicotinamide adenine dinucleotide
o NADP+ = nicotinamide adenine dinucleotide phosphate
• Nicoinamide (form found in animal cells)
o Free nicotinamide is released from NAD/NADP
o This is the main circulating source of niacin in the blood
Niacin in the body:
• In foods, niacin can be bound covalently to other macronutrients
o Bound to complex carbohydrates (e.g. fiber) = niacytin
o Bound to small peptides = niacinogens
• Niacinogens are the primary form of niacin found in corn
o Corn must be chemically treated with bases (e.g. lime water) to improve the
bioavailability of niacin
o Pellagra (niacin deficiency) results in populations consuming high corn-based diets that
don’t proves the corn with basic solutions
• In the liver, NAD and NADP can be synthesized from tryptophan (biologically possible, but
inefficient)
o Inefficient pathway: 1 mg niacin is produced from the ingestion of 60mg of dietary
tryptophan
• Role of Niacin in Redox:
o NAD+ (oxidized) – dominant pool, 10-fold excess over NADH mainly due to activity
of ETC
o NADH (reduced NAD)
o NADPH (reduced NADP) – dominant pool, 10-fold excess over NADP+
regenerated/produced by pentose phosphate pathway (hexose monophosphate shunt)
o NADP+ (oxidized NADP)
• These coenzymes act as 2 electron acceptors (as NAD+) or donors (as NADPH) in a number of
reactions
• Niacin is also involved in the addition of ADP-ribose to proteins associated with DNA repair
Health Consequences of Niacin Deficiency Pellagra
• Disease of pellagra is characterized by the 4 “D’s”
o Diarrhea
o Dermatitis (sun exposure)
o Dementia
o Death
• Niacin deficiency in dogs black tongue
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