Niacin Flashcards
(22 cards)
What are the two main forms of niacin?
Nicotinic acid and Nicotinamide (niacinamide)
These forms are both essential for various metabolic functions.
What is the physical properties of niacin? what is it also reffered to?
White crystalline structure, soluble in water and alcohol, stable to heat, oxidation, and light
Vit B3
Niacin is not destroyed by UV light unlike riboflavin.
What are the active forms of niacin? where is the active site?
NAD (Nicotinamide Adenine Dinucleotide) and NADP (Nicotinamide Adenine Dinucleotide Phosphate)
The active site is the nicotinamide ring
-involved in redox reactions
These forms act as coenzymes in redox reactions.
What role does NAD play in metabolism? what pathways is it involved in?
Involved in catabolic (energy-producing) reactions such as glycolysis, TCA cycle, electron transport chain, β-oxidation, and amino acid metabolism
NAD is crucial for breaking down nutrients to generate energy.
What is the function of NADP in metabolism? what pathways is it involved in?
Involved in anabolic (biosynthetic) reactions, including the pentose phosphate pathway and fatty acid synthesis
NADP helps synthesize molecules and maintain redox balance.
what is the role of niacin in the PDH complex?
Niacin is needed to make NAD+ cofactor
-final transfer of H+ from FADH2
what is pantothenic acid?
A structure that acts as part of a coA
What is ADP-ribosylation?
1) ADP-ribosylation: A non cofactor role of niacin where the addition of NAD to a protein causes it to act as a substrate (no NADH production)
-regulates DNA repair, immune responses, and metabolism
Enzymes like PARP rely on NAD for fixing damaged DNA.
What non cofactor role, other than ribosylation, does niacin play? what is used? what is the downside of this?
reduction of cholesterol and TG using nicotinic acid
-can attach to recpetors and release histamines which increase vasodilation and may cause bruising
What is the effect of high-dose nicotinic acid on cholesterol?
It lowers cholesterol and triglycerides and has an anti-lipolytic effect
This reduces free fatty acid release from adipose tissue.
How is niacin synthesized in the body? what is needed for this to occur?
From tryptophan in the liver, requiring Vitamin B6 and Riboflavin
60 mg of tryptophan produces 1 mg of niacin. Normal intakes of Trp are adequate for sythesis
what vitamins are needed for niacin synthesis?
B6 (pyroxidine)
Riboflavin
Vit C
How is niacin absorbed in the body?
Absorbed in the small intestine via facilitated diffusion at low concentrations and passive diffusion at high concentrations
Dephosphorylated for absorption and phosphorylated for storage
Nicotinic acid can also be absorbed in the stomach by passive diffusion
What happens to niacin after absorption? how is it stored? how is it excreted?
Converted into NAD in the liver, with surplus released into circulation as nicotinamide or nicotinic acid
Minimal storage as NAD or NADP in tissues; more storage in cytoplasm bound to tissues
Excreted in the urine, minimal loss with modest intake
What dietary sources provide preformed niacin? what are indirect sources of niacin?
Typically bound to protein: Meat, poultry, fish, legumes, peanuts, some cereals, enriched grain products, dairy, and eggs
Eggs are a good source of tryptophan which can be converted into niacin
what is the bioavailibility of niacin?
niacin in cereals (bran) are not available
-> milling removes bran
Nicotinic acid is bound to complex CHO and protein
What is the minimum daily requirement of niacin? what unit is this in? why? what is the UL?
7mg NE- since niacin can be made from tryptophan (14mg minimum)
The upper limit is 35 mg/day due to risks associated with higher intake.
How is niacin status determined?
1) Tyrpotophan, Pyroxine, Leucine
2) whole body NAD/NADP concentrations
What is Pellagra? what is a common risk factor?
A condition resulting from niacin deficiency characterized by dermatitis, diarrhea, and dementia
Consuming untreated foods where niacin is unavailble and Trp is low (corn and sorghum)
-alkaline substances (limewater) liberates nicotinic acid
If untreated, it can lead to death.
What are the symptoms of Pellagra?
Dermatitis, diarrhea, dementia
These symptoms are commonly referred to as the ‘3 Ds’.
True or False: Niacin is stable to heat and light.
True
Unlike some other vitamins, niacin remains intact under these conditions.
Fill in the blank: Niacin can be synthesized from _______ in the liver.
tryptophan
