Niacin Flashcards
niacin, thiamin, and riboflavin are needed in __ amounts
niacin, thiamin, and riboflavin are needed in very small amounts
4 general aspects of niacin, thiamin, and riboflavin
- variable heat-resistance. alkaline-labile, sensitive to light
- present in most food sources
- excreted mainly through urine
- deficiency is rare in developed countries, but certain groups are at risk
why does heat resistance of vitamins matter
we need to know what cooking provess is appropriate
how are niacin, thiamin, and riboflavin excreted
urine
niacin aka
NIcotinic ACid vitamIN
niacin refers to
nicotinic acid (niacin) AND nicotinamide (niacinamide)
niacin aka
nicotnic acid
niacinamide aka
nicotinamide
main function of niacin
precursor for NAD and NADP
NAD and NADP are __ molecules
NAD and NADP are oxidizing molecules
active niacin can be made from
- tryptophan
- nicotnic acid
- nicotinamide
humans can synthesize niacin from
tryptophan
if we have enough __, we may not need to consume niacin, BUT __
if we have enough tryptophan, we may not need to consume niacin, BUT it is hard to consume that much Trp
which of these foods contain niacin?
ALL OF THE ABOVE
foods with high niacin content
- meats
- poultry
- fish
- legumes
- peanuts
- cereals
- enriched flours and cereals
what forms of niacin can enterocyte absorb directly?
nicotinamide and nicotinic acid
NAD+ and NADP absorption into enterocyte
CAN’T be directly absorbed
must be broken down and reassembled
niacin is found mostly in __ bound forms __ and __
niacin is found mostly in covalently bound forms NAD+ and NADP
niacin in __ is naturally NOT bioavailable
niacin in grains (bran) is naturally NOT bioavailable
1 mg niacin = __ mg tryptophan (~_ g good quality protein)
1 mg niacin = 60 mg tryptophan (~6 g good quality protein)
the average US diet contains enough __ for niacin requirement through synthesis of __
the average US diet contains enough protein for niacin requirement through synthesis of tryptophan
at low conc, niacin is absorbed via
carrier-mediated, Na-dependent facilitated diffusion
where is glycohydrolase found?
all cells
shortcut for NAD/NADP degradation
glycohydrolase turns NAD and NADP directly into nicotinamide
steps of niacin absorption
- NAD, NADP –> NMN (enzyme: phosphatase)
- NMN –> nicotinamide riboside (enzyme: phosphatase)
- nicotinamide riboside –> nicotinamide (hydratase)
- nicotinamide absorbed into enterocyte
de novo pathway diversion
ACMS to AMS (by ACMSD) to acetyl-CoA
de novo pathway steps
tryptophan –> ACMS –> NAD
what happens to the following once they enter the enterocyte:
NMN
nicotinamide
nicotnic acid
ALL enter portal circulation (mainly nicotinamide) (NMN as NAD) and go to liver
liver distributes to rest of body
at high conc, niacin is absorbed via
passive diffusion
NAD+ is synthesized by 3 pathways
- de novo pathway
- Preiss-Handler pathway
- Salvage pathway
where is de novo pathway most active?
liver and kidney
which organ uses all 3 pathways?
the liver
preiss-handler converts
nicotinic acid to NAD+
high fat, high leucine diet, and diabetic ketoacidosis __ niacin synthesis by inducing __
high fat, high leucine diet, and diabetic ketoacidosis reduce niacin synthesis by inducing ACMSD
preiss-handler requires a lot of __ and is only used when there is __
preiss-handler requires a lot of energy and is only used when there is excess
salvage pathway recycles __ to yield __ and is used by __
salvage pathway recycles NADP to yield nicotinamide and is used by sirtuins (SIRT)
people deficient in __, __, and __ will be niacin deficient bc __
people deficient in iron, riboflavin, and vit B6 will be niacin deficient bc they are all required to synthesize NAD
what enzyme diverts synthesis of NAD to acetyl-CoA?
ACMSD
liver uptakes __, __, and __ and converts them to NAD
liver uptakes nicotinamide, nicotnic acid, and tryptophan and converts them to NAD
what enzyme converts NAD+ to nicotinamide
NAD+ glycohydrolase
can the liver store NAD?
yes, but just some
main niacin form in blood
nicotinamide
degradation of niacin in liver
nicotinamide is __ to __
nicotinic acid is __ to __
untransformed niacin found during __
degradation of niacin in liver
nicotinamide is methylated to N1-methyl-nicotinamide
nicotinic acid is conjugated to nicotinuric acid
untransformed niacin found during high niacin diet
tissues rapidly convert nicotinamide and nicotinic acid to __ and __
tissues rapidly convert nicotinamide and nicotinic acid to NAD and NADP
NAD pool is mostly __ due to ETC activity
NAD pool is mostly NAD+ due to ETC activity
NADP pool is mostly __ due to PPP
NADP pool is mostly NADPH due to PPP
NAD can function as a __ or __
NAD can function as a coenzyme or substrate
NAD as a coenzyme
__ and __ are electron acceptors of hydrogen donors in rxns
NAD as a coenzyme
NAD and NADP are electron acceptors of hydrogen donors in rxns
NAD as a substrate
__ acts as a donor of ADP-ribose for __ modification of proteins
NAD as a substrate
NAD+ acts as a donor of ADP-ribose for posttranslational modification of proteins
PARPs create more __ chromatin
PARPs create more relaxed chromatin
sirtuins (SIRT) create more __ chromatin
sirtuins (SIRT) create more condensed chromatin
what kind of enzyme are SIRTs?
what do they do to chromatin?
deacetylases
condense chromatin
PARPs and SIRTs turn __ to __
PARPs and SIRTs turn NAD+ to nicotinamide
2 sources of substrate for ADP-ribosylation of proteins or acetyl groups
__ is released in reaction
- PARP
- Sirtuins (SIRT)
nicotinamide is released in reaction
why do NAD+ levels oscillate in a circadian fashion?
differential expression of NAMPT (rate-limiting enzyme in NAD salvage pathway)
affects SIRTs
NAD+ levels oscillate in __ fashion in all cell types
NAD+ levels oscillate in circadian fashion in all cell types
how to determine niacin status?
urinary excretion of niacin metabolites
determining niacin status: look at
ratio btwn NMN (substrate) and its oxidized product
niacin deficiency
Pellagra
pellgra symptoms
4 Ds
diarrhea, dermatitis, dementia, death
people at risk for Pellagra
- low protein
- aloholics
- cancer
- genetic disorder
pellagra is seasonal bc
sun-exposed skin more commonly has rash
sunlight breaks down DNA, no way to repair without niacin
can we store niacin
no
what is the only water soluble vitamin we can store
B12
Hartnup disease is a mutation in the __ transporter
Hartnup disease is a mutation in the tryptophan transporter
Hartnup disease
- autosomal recessive disorder
- mutation in SLCA19 gene
- defective transport of tryptophan
- manifests like Pellagra
how to treat Hartnup disease?
niacin pills, high protein diet, avoid sun
niacin can also be used to treat
artherosclerosis
niacin is vitamin
B3