Niacin

Question 1

What are the metabolically active forms of niacin?

Answer 1

NAD+ (nicotinamide adenine dinucleotide)
NADP - nicotinamide adenine dinucleotide phosphate
NMN - nicotinamide mononucleotide

Question 2

How is the structure of metabolically active niacin similar to metabolically active riboflavin?

Answer 2

FAD+ –> FADH2 (riboflavin)
FAD = flavin adenine dinucleotide
- usually bound
- accept 1 electron at a time

NAD+ –> NADH (niacin)

• usually floating around
• accepts electrons 2 at a time as a hydride

Question 3

How is the biochemical function of niacin similar to/different from that of riboflavin?

Answer 3

FAD is usually bound and can accept 1 electron at a time

NAD is usually floating around (not bound like FAD) and can accept 2 electrons at a time

Similarities between FAD and NAD are that they both are electron acceptors.

Question 4

What is the main disease state associated with severe niacin deficiency?

Answer 4

Pellagra

Symptoms: the three “Ds” => sun-sensitive dermatitis, diarrhea, and dementia (the fourth “D” is death)

Question 5

What is the RDA for Niacin in adults?

Answer 5

Males: 16 mg NE/day
Females: 14 mg NE/day

NE = niacin equivalent
60 mg tryptophan = 1 mg niacin = 1 mg NE

Question 6

What are the metabolic roles of NAD(H) and NADP(H)?

Answer 6

NAD(H) = nicotinamide adenine dinucleotide (hydrogen)
Function: degradation (catabolism) of CHO, fats, proteins, and alcohol
- oxidation/reduction reactions (TCA cycle)

NADP(H) = nicotinamide adenine dinucleotide phosphate
Function: biosynthetic (anabolic) reactions, synthesis of fatty acids, steroids, and building blocks of other macromolecules.
Also essential for the regeneration of components of detoxification and antioxidant systems.

Question 7

What are the two niacin coenzymes?

Answer 7

NAD and NADP

Question 8

What is the function of NAD+ in the TCA cycle?

Answer 8

Transports and accepts electrons in the TCA cycle

NAD+ transfers electrons to form NADH and releases CO2 (oxidation reaction)

NAD+ helps pyruvate dehydrogenase to convert pyruvate to acetyl-CoA which then enters the TCA cycle

NAD+ is also reduced to NADH as isocitrate is oxidized and releases a molecule of CO2 (leaving behind an alpha-ketoglutarate)

The enzyme in this reaction: isocitrate dehydrogenase - catalyzing step of the cycle - an important role in the speed of the TCA cycle occurring

Question 9

What are the 4 dietary precursors of NAD+ in the diet?

Answer 9

1. nicotinamide mononucleotide (NMN)
2. nicotinamide (NAM)
3. nicotinamide riboside (NR)
4. tryptophan

Question 10

What are common dietary sources of niacin?

Answer 10

salmon
spinach
nuts
lean meats
legumes

Question 11

What are the biological functions associated with NAD+?

Answer 11

sole substrate (molecule upon which an enzyme acts) for important enzymes such as:

• DNA repair enzymes
• PARP (poly-ADP ribose polymerase) - a critical enzyme involved in DNA repair
• Histone diacylation by sirtuin enzymes associated with transcriptional regulation
• aging and longevity