asam amino & vitamin

8/14/2019 Asam Amino & Vitamin

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Metabolic functions of vitamin A

Vitamin A plays a role in a variety of functions throughout the body, such as:

Vision

Gene Transcription Immune Function

Embryonic Development and eproduction

!one "etabolism

#aematopoiesis

$%in #ealth

educing is% of #eart Disease and &ancer

Antio'idant Activity

[edit] Vision

The role of vitamin A in the vision cycle is specifically related to the retinal form( )ithin

the eye, **+cis+retinal is bound to rhodopsin rods- and iodopsin cones- at conserved

lysine residues( As light enters the eye the **+cis+retinal is isomeri.ed to the all+/trans/form( The all+/trans/ retinal dissociates from the opsin in a series of steps called

bleaching( This isomeri.ation induces a nervous signal along the optic nerve to the visual

center of the brain( 0pon completion of this cycle, the all+/trans/+retinal can be recycledand converted bac% to the **+/cis/+retinal form via a series of en.ymatic reactions(

Additionally, some of the all+/trans/ retinal may be converted to all+/trans/ retinol form

and then transported 1ith an interphotoreceptor retinol+binding protein I!2- to thepigment epithelial cells( Further esterification into all+/trans/ retinyl esters allo1 this

final form to be stored 1ithin the pigment epithelial cells to be reused 1hen needed( 3*45

The final conversion of **+cis+retinal 1ill rebind to opsin to reform rhodopsin in the

retina( hodopsin is needed to see blac% and 1hite as 1ell as see at night( It is for thisreason that a deficiency in vitamin A 1ill inhibit the reformation of rhodopsin and lead to

night blindness(3*65

[edit] Gene transcription

Vitamin A, in the retinoic acid form, plays an important role in gene transcription( 7nce

retinol has been ta%en up by a cell, it can be o'idi.ed to retinal by retinoldehydrogenases- and then retinal can be o'idi.ed to retinoic acid by retinal o'idase-(

The conversion of retinal to retinoic acid is an irreversible step, meaning that theproduction of retinoic acid is tightly regulated, due to its activity as a ligand for nuclearreceptors(3*45etinoic acid can bind to t1o different nuclear receptors to initiate or

inhibit- gene transcription: the retinoic acid receptors As- or the retinoid /8/

receptors 8s-( A and 8 must dimeri.e before they can bind to the D9A( A1ill form a heterodimer 1ith 8 A+8-, but it does not readily form a

homodimer A+A-( 8, on the other hand, readily forms a homodimer 8+

8- and 1ill form heterodimers 1ith many other nuclear receptors as 1ell, including
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the thyroid hormone receptor 8+T-, the Vitamin D4receptor 8+VD-, the

pero'isome proliferator+activated receptor 8+22A- and the liver /8/ receptor

8+8-(3*;5The A+8 heterodimer recogni.es retinoid acid response elementsAEs- on the D9A 1hereas the 8+8 homodimer recogni.es retinoid /8/

response elements 8Es- on the D9A( The other 8 heterodimers 1ill bind to

various other response elements on the D9A(3*45

7nce the retinoic acid binds to thereceptors and dimeri.ation has occurred, the receptors undergo a conformational change

that causes co+repressors to dissociate from the receptors( &oactivators can then bind to

the receptor comple', 1hich may help to loosen the chromatin structure from the histonesor may interact 1ith the transcriptional machinery(3*;5The receptors can then bind to the

response elements on the D9A and upregulate or do1nregulate- the e'pression of target

genes, such as cellular retinol+binding protein &!2- as 1ell as the genes that encode

for the receptors themselves(3*45

[edit] Dermatology

Vitamin A appears to function in maintaining normal s%in health( The mechanismsbehind retinoid


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chronic malabsorption of lipids, impaired bile production and release, lo1 fat diets, and

chronic e'posure to o'idants, such as cigarette smo%e( Vitamin A is a fat soluble vitamin

and depends on micellar solubili.ation for dispersion into the small intestine, 1hichresults in poor utili.ation of vitamin A from lo1+fat diets( inc deficiency can also impair

absorption, transport, and metabolism of vitamin A because it is essential for the

synthesis of the vitamin A transport proteins and the o'idation of retinol to retinal( Inmalnourished populations, common lo1 inta%es of vitamin A and .inc increase the ris% of

vitamin A deficiency and lead to several physiological events(3*45A study in !ur%ina Faso

sho1ed maor reduction of malaria morbidity 1ith combined vitamin A and.incsupplementation in young children(3*B5

$ince the uniue function of retinyl group is the light absorption in etinylidene protein,

one of the earliest and specific manifestations of vitamin A deficiencyis impaired vision,

particularly in reduced light +9ight blindness(2ersistent deficiency gives rise to a seriesof changes, the most devastating of 1hich occur in the eyes( $ome other ocular changes

are referred to as 'erophthalmia(First there is dryness of the conunctiva 'erosis- as the

normal lacrimal and mucus secreting epithelium is replaced by a %eratini.ed epithelium(This is follo1ed by the build+up of %eratin debris in small opaue plaues !itot+*; months(3?45#o1ever, liver

to'icities can occur at levels as lo1 as *;,@@@ I0 per day to *(6 million I0 per day, 1ithan average daily to'ic dose of *?@,@@@ I0 per day( In people 1ith renal failure6@@@ I0

can cause substantial damage( Additionally e'cessive alcohol inta%e can increase to'icity(

&hildren can reach to'ic levels at *;@@I0%g of body 1eight(3?65
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In chronic cases, hair loss, drying of the mucous membranes, fever, insomnia, fatigue,

1eight loss, bone fractures, anemia, and diarrhea can all be evident on top of the

symptoms associated 1ith less serious to'icity(3?;5

It has been estimated that ;H of people may be ingesting more than the DA for

vitamin A on a regular basis in developed nations( Inta%e of t1ice the DA of preformedvitamin A chronically may be associated 1ith osteoporosis and hip fractures( #igh

vitamin A inta%e has been associated 1ith spontaneous bone fractures in animals( &ellculture studies have lin%ed increased bone resorption and decreased bone formation 1ith

high vitamin A inta%es( This interaction may occur because vitamins A and D may

compete for the same receptor and then interact 1ith parathyoid hormone 1hich regulatescalcium(3?65

To'ic effects of vitamin A have been sho1n to significantly affect developing fetuses(

Therapeutic doses used for acne treatment have been sho1n to disrupt cephalic neural

cell activity( The fetus is particularly sensitive to vitamin A to'icity during the period of

organogenesis(

3*45

These to'icities only occur 1ith preformed retinoid- vitamin A such as from liver-( The

carotenoid forms such as beta+carotene as found in carrots-, give no such symptoms, but

e'cessive dietary inta%e of beta+carotene can lead to carotenodermia, 1hich causesorange+yello1 discoloration of the s%in(3?>53?53?C5

A study by $iri Forsmo et al.sho1s a correlation bet1een lo1 bone mineral density and

too high inta%e of vitamin A(3?B5

esearchers have succeeded in creating 1ater+soluble forms of vitamin A, 1hich they

believed could reduce the potential for to'icity(

34@5

#o1ever, a ?@@4 study found that1ater+soluble vitamin A 1as appro'imately *@ times as to'ic as fat+soluble vitamin(34*5A

?@@> study found that children given 1ater+soluble vitamin A and D, 1hich are typicallyfat+soluble, suffer from asthma t1ice as much as a control group supplemented 1ith the

fat+soluble vitamins(34?5

&hronically high doses of Vitamin A can produce the syndrome of /pseudotumor

cerebri/(3445This syndrome includes headache, blurring of vision and confusion( It isassociated 1ith increased intracerebral pressure(34

Vitamin B4(adenine, DNA metabolite) is no longer classified as a vitamin

because it is synthesied by the human body

3citation needed5

Vitamin B8(myo!inositol, adenylic acid, DNA metabolite) is no longer classified

as a vitamin because it is synthesied by the human body3citation needed5

Vitamin B15(pangamic acid) is not "idely accepted as a vitamin because it has

not been sho"n to be essential in the human diet#citation needed$

Vitamin B17(amygdalin, laetrille) is not yet classified#citation needed$

[edit] B vitamin deficiency
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$everal named vitamin deficiency diseases may result from the lac% of sufficient !+

vitamins( Deficiencies of other ! vitamins result in symptoms that are not part of a

named deficiency disease(

Vitamin Name Deficiency effects

Vitamin

Bthiamine

Deficiency causesberiberi($ymptoms of this disease of thenervous systeminclude 1eight loss, emotional disturbances,)ernic%e


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"any of the follo1ing substances have been referred to as vitamins because they 1ere

believed to be vitamins at one time, and they are relevant to vitamin nomenclature in that

the numbers that 1ere assigned to them form /gaps/ in the series of !+vitamin names($ome of them, though not essential to humans, are essential in the diets of other

organisms= others have no %no1n nutritional value(

Vitamin B(: Adenine, a nucleobase(3*5

Vitamin B%: /Vitamin I/ of &entanni E( *B4;- J also called


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9ote: B$, B%, B), B&, B!*, B!M B!!do not appear to be animal factors but are claimed

by some naturopaths as human therapedic factors(

[edit] .ealt+ benefits

The ! vitamins often 1or% together to deliver a number of health benefits to the body( !vitamins have been sho1n to:

$upport and increase the rate of metabolism

"aintain healthy s%in and muscle tone

Enhance immuneand nervous systemfunction

2romote cell gro1thand divisionJ including that of the red blood cellsthat help

prevent anemia(

educe the ris% ofpancreatic cancer,one of the most lethal forms of cancer345,

1hen consumed in food, but not 1hen ingested in vitamin tablet form(3653;5

Together, they also help combat the symptoms and causes of stress,depression, andcardiovascular disease(

All ! vitamins are 1ater soluble, and are dispersed throughout the body( "ost of the !

vitamins must be replenished daily, since any e'cess is e'creted in the urine(3>5A si' yearcobalamin store can be found in the liver, despite its 1ater soluble nature(3citation needed5

[edit] Vitamin B sources

Different ! vitamins come from different natural sources, such aspotatoes,bananas,

lentils, chile peppers, tempeh,liver oil, liver, tur%ey,tuna,9utritional yeastorbre1er


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are also commonly added to energy drin%s( "any energy drin%s have been mar%eted 1ith

large amounts of ! vitamins /;+#our Energy contains an astounding C,444H of the

recommended dietary allo1ance of vitamin !+*? and ?,@@@H of the DA for vitamin !+>(N ed !ullNoffers 4>@H of the DA for vitamin !+>, *?@H of !*?, *6@H of niacin

vitamin !4-/3**5- 1ith claims that this 1ill cause the consumer to /sail through your day

1ithout feeling ittery or tense(/3**5

9utritionists, such as 2rofessor #ope !ar%ou%is,dismiss these claims /It


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3hide5

* #istory

? Dietary needs

4 2harmacological uses

o 4(* ipid modifying effects

o 4(? Topical useo 4(4 9iacin and drug screening tests

6 To'icity

; Inositol he'anicotinate

> !iosynthesis

eceptor

C Food sources

B eferences

[edit] .istory9iacin 1as first described by #ugo )eidelin *C4 in his studies of nicotine(365Theoriginal preparation remains useful: the o'idation of nicotine using nitric acid(3;59iacin

1as e'tracted from livers by &onrad Elvehem1ho later identified the activeingredient,

then referred to as the /pellagra+preventing factor/ and the /anti+blac%tongue factor(/3>5

)hen the biological significance of nicotinic acid 1as reali.ed, it 1as thoughtappropriate to choose a name to dissociate it from nicotine, in order to avoid the

perception that vitamins or niacin+rich food contains nicotine( The resulting name


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9ote: 9iacin synthesis is deficient in carcinoid syndromebecause of metabolic diversion

of its precursor, tryptophan, to form serotonin(

[edit] /+armacologicaluses

The recommended daily allo1ance DA- for niacin is ?@ mgday( The argument thatniacin does not provide any benefits at doses above the DA has been decisively

disproven(3citation needed5There are t1o decisively proven uses of pharmacological doses of

niacin( These are for heart disease and s%in conditions( E'tensive evidence combining%no1n biochemical functions of vitamin !4, controlled trials, and clinical observations

indicate that doses of niacin above the DA speed 1ound healingand help the immune

system fight off viral infections( The available evidence supports the hypothesis thatresponse is proportional to dose 1ell past the side effect threshold( The side effect

threshold for niacin varies dramatically from person to person, ranging from bet1een 4@

and 4@@ mg for the maority of the population(

[edit] -ipid modifying effects

9iacin, prescribed in doses bet1een *@@@ and ?@@@ mg t1o to three times daily, 3*@5bloc%s the brea%do1n of fatsin adipose tissue, a very+lo1+density lipoproteinVD-, a

precursor of lo1+density lipoproteinD- or /bad/ cholesterol( !ecause niacin bloc%s

brea%do1n of fats, it causes a decrease in free fatty acidsin the blood and, as a

conseuence, decreased secretion of VD and cholesterol by the liver(3**5

!y lo1ering VD levels, niacin also increasesthe levelof high+density lipoprotein

#D- or /good/ cholesterol in blood, and therefore it is sometimes prescribed for

patients 1ith lo1 #D, 1ho are also at high ris% of a heart attac%(3*?53*45

As of August ?@@C, a combination of niacin 1ith laropiprantis tested in a clinical trial(aropiprant reduces facial flushes induced by niacin(

[edit] Topical use

A fat+soluble derivative of niacin has been developed that efficiently penetrates the s%in(This form of niacin has been sho1n to improve a variety of s%in conditions in a number

of controlled clinical trials(

[edit] Niacin and drug screening tests

9iacin is sometimes consumed in large uantities by people 1ho 1ish to fool drug

screening tests, particularly for lipid solubledrugs such as mariuana(3*65It is believed to/promote metabolism/ of the drug and cause it to be /flushed out(/ $cientific studies have

sho1n it does not affect drug screenings, but can pose a ris% of overdose, causing

arrhythmias, metabolic acidosis, hyperglycemia, and other serious problems(3*;5
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[edit] Toxicity

2eople ta%ing pharmacological doses of niacin *(; + > g per day- often e'perience a side+

effects that can include dermatological complaints such as facial flushing and itching, drys%in, s%in rashes including acanthosis nigricans( Gastrointestinal complaints, such as

dyspepsiaindigestion- and liver to'icity fulminant hepatic failure- have also beenreported( Also reported include hyperglycemia, cardiac arrhythmias, birth defects, andorthostasis(3*>5

Facial flushing is the most commonly reported side effect(3*5It lastsfor about *; to 4@

minutes, and is sometimes accompanied by a pric%ly or itching sensation, particularly in

areas covered by clothing( This effect is mediated byprostaglandinand can be bloc%edby ta%ing 4@@ mg of aspirinhalf an hour before ta%ing niacin, or by ta%ing one tablet of

ibuprofenper day( Ta%ing the niacin 1ith meals also helps reduce this side effect( After *

to ? 1ee%s of a stable dose, most patients no longer flush(3citation needed5$lo1+ or /sustained/+release forms of niacin havebeen developed to lessen these side+effects( 3**53*C57ne study

sho1ed the incidence of flushing 1as significantly lo1er 1ith a sustained releaseformulation3*B5though doses above ? g per day have been associated 1ith liver damage,

particularly 1ith slo1+release formulations(3*>5

#igh+dose niacin may also elevateblood sugar, thereby 1orsening diabetes mellitus(3*>5

#yperuricemiais another side+effect of ta%inghigh+dose niacin, and may e'acerbate

gout(3?@59iacin at doses used in lo1ering cholesterol has been associated 1ith birthdefects in laboratory animals, 1ithpossible conseuences for infant development in

pregnant1omen(3*>5

9iacin at e'tremely high doses can have life+threatening acute to'ic reactions(3?*5

E'tremely high doses of niacin can also cause niacin maculopathy, a thic%ening of themaculaand retina1hich leads to blurred vision and blindness( This maculopathy is

reversible after stopping niacin inta%e(3??5

[edit] 2nositol +exanicotinate

7ne popular form of dietary supplement is inositol he'anicotinate, usually sold as /flush+free/ or/no+flush/ niacin although those terms are also used for regular sustained+

release(- )hile this form of niacin does not cause the flushing associated 1ith the

nicotinic acid form, it is not pharmacologically euivalent in its positive effect(3?45

2rescription grade niacin is available and is proven to reduce cholesterol( Thus far thereis not enough evidence to recommend inositol he'anicotinate to treat dyslipidemia(

9iacin 1hen ta%en in slo1ly increasing doses 1ill cause far less flushing(

[edit] Biosynt+esis
http://en.wikipedia.org/wiki/Arrhythmiahttp://en.wikipedia.org/wiki/Arrhythmiahttp://en.wikipedia.org/wiki/Arrhythmiahttp://en.wikipedia.org/wiki/Metabolic_acidosishttp://en.wikipedia.org/w/index.php?title=Niacin&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Niacin&action=edit&section=7http://en.wikipedia.org/wiki/Hyperglycemiahttp://en.wikipedia.org/wiki/Cardiac_arrhythmiashttp://en.wikipedia.org/wiki/Cardiac_arrhythmiashttp://en.wikipedia.org/wiki/Cardiac_arrhythmiashttp://en.wikipedia.org/wiki/Niacin#cite_note-G.26G-15http://en.wikipedia.org/wiki/Niacin#cite_note-16http://en.wikipedia.org/wiki/Prostaglandinhttp://en.wikipedia.org/wiki/Prostaglandinhttp://en.wikipedia.org/wiki/Prostaglandinhttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Ibuprofenhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Niacin#cite_note-pmid15324528-18http://en.wikipedia.org/wiki/Hepatotoxicityhttp://en.wikipedia.org/wiki/Hepatotoxicityhttp://en.wikipedia.org/wiki/Hepatotoxicityhttp://en.wikipedia.org/wiki/Niacin#cite_note-G.26G-15http://en.wikipedia.org/wiki/Blood_sugarhttp://en.wikipedia.org/wiki/Diabetes_mellitushttp://en.wikipedia.org/wiki/Hyperuricemiahttp://en.wikipedia.org/wiki/Hyperuricemiahttp://en.wikipedia.org/wiki/Pregnancyhttp://en.wikipedia.org/wiki/Niacin#cite_note-G.26G-15http://en.wikipedia.org/wiki/Niacin#cite_note-pmid15035390-21http://en.wikipedia.org/w/index.php?title=Niacin&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Niacin&action=edit&section=8http://en.wikipedia.org/wiki/Arrhythmiahttp://en.wikipedia.org/wiki/Metabolic_acidosishttp://en.wikipedia.org/wiki/Hyperglycemiahttp://en.wikipedia.org/wiki/Niacin#cite_note-14http://en.wikipedia.org/w/index.php?title=Niacin&action=edit&section=7http://en.wikipedia.org/wiki/Acanthosis_nigricanshttp://en.wikipedia.org/wiki/Dyspepsiahttp://en.wikipedia.org/wiki/Fulminant_hepatic_failurehttp://en.wikipedia.org/wiki/Hyperglycemiahttp://en.wikipedia.org/wiki/Cardiac_arrhythmiashttp://en.wikipedia.org/wiki/Niacin#cite_note-G.26G-15http://en.wikipedia.org/wiki/Niacin#cite_note-16http://en.wikipedia.org/wiki/Prostaglandinhttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Ibuprofenhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Niacin#cite_note-Katzung-10http://en.wikipedia.org/wiki/Niacin#cite_note-17http://en.wikipedia.org/wiki/Sustained_releasehttp://en.wikipedia.org/wiki/Niacin#cite_note-pmid15324528-18http://en.wikipedia.org/wiki/Hepatotoxicityhttp://en.wikipedia.org/wiki/Niacin#cite_note-G.26G-15http://en.wikipedia.org/wiki/Blood_sugarhttp://en.wikipedia.org/wiki/Diabetes_mellitushttp://en.wikipedia.org/wiki/Niacin#cite_note-G.26G-15http://en.wikipedia.org/wiki/Hyperuricemiahttp://en.wikipedia.org/wiki/Gouthttp://en.wikipedia.org/wiki/Niacin#cite_note-pmid11122726-19http://en.wikipedia.org/wiki/Pregnancyhttp://en.wikipedia.org/wiki/Niacin#cite_note-G.26G-15http://en.wikipedia.org/wiki/Niacin#cite_note-pmid17418450-20http://en.wikipedia.org/wiki/Maculahttp://en.wikipedia.org/wiki/Retinahttp://en.wikipedia.org/wiki/Niacin#cite_note-pmid15035390-21http://en.wikipedia.org/w/index.php?title=Niacin&action=edit&section=8http://en.wikipedia.org/wiki/Niacin#cite_note-22http://en.wikipedia.org/w/index.php?title=Niacin&action=edit&section=9


12/13

!iosynthesis: TryptophanQ %ynurenineQ niacin

!iosynthesis

The livercan synthesi.e niacin from the essential amino acidtryptophan, reuiring >@ mg

of tryptophan to ma%e one mg of niacin(3?65

The ;+membered aromaticheterocycleof tryptophan is cleaved and rearranged 1ith thealpha amino groupof tryptophan into the >+membered aromatic heterocycle of niacin(

[edit] 'eceptor
http://en.wikipedia.org/wiki/Tryptophanhttp://en.wikipedia.org/wiki/Kynureninehttp://en.wikipedia.org/wiki/Liverhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Tryptophanhttp://en.wikipedia.org/wiki/Gram#SI_multipleshttp://en.wikipedia.org/wiki/Niacin#cite_note-OSU-23http://en.wikipedia.org/wiki/Aromatichttp://en.wikipedia.org/wiki/Aromatichttp://en.wikipedia.org/wiki/Heterocyclic_compoundhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/w/index.php?title=Niacin&action=edit&section=10http://en.wikipedia.org/wiki/Image:Tryptophan_metabolism.pnghttp://en.wikipedia.org/wiki/Image:Tryptophan_metabolism.pnghttp://en.wikipedia.org/wiki/Image:Niacin_biosynthesis.svghttp://en.wikipedia.org/wiki/Image:Niacin_biosynthesis.svghttp://en.wikipedia.org/wiki/Tryptophanhttp://en.wikipedia.org/wiki/Kynureninehttp://en.wikipedia.org/wiki/Liverhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Tryptophanhttp://en.wikipedia.org/wiki/Gram#SI_multipleshttp://en.wikipedia.org/wiki/Niacin#cite_note-OSU-23http://en.wikipedia.org/wiki/Aromatichttp://en.wikipedia.org/wiki/Heterocyclic_compoundhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/w/index.php?title=Niacin&action=edit&section=10


13/13

The receptor for niacin is aG protein+coupled receptorcalled #"6A(3?;5It couples to Gi

alpha subunit(3?>5

[edit] 3ood sources

9iacin is essentially found in meat, 1heat germ, dairy products, and yeast(

Animalproducts43ruitsand

vegetables45eeds4 3ungi4

liver,heart

and %idney

chic%en

beef

fish: tuna,

salmon

mil%

eggs

leaf

vegetables

broccoli

tomatoes

carrots

dates

s1eet potatoes

asparagus

avocados
http://en.wikipedia.org/wiki/G_protein-coupled_receptorhttp://en.wikipedia.org/wiki/G_protein-coupled_receptorhttp://en.wikipedia.org/wiki/Niacin#cite_note-pmid16018973-24http://en.wikipedia.org/wiki/Gi_alpha_subunithttp://en.wikipedia.org/wiki/Gi_alpha_subunithttp://en.wikipedia.org/wiki/Gi_alpha_subunithttp://en.wikipedia.org/wiki/Niacin#cite_note-pmid15580557-25http://en.wikipedia.org/w/index.php?title=Niacin&action=edit&section=11http://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Fruitshttp://en.wikipedia.org/wiki/Vegetableshttp://en.wikipedia.org/wiki/Seedshttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Liverhttp://en.wikipedia.org/wiki/Hearthttp://en.wikipedia.org/wiki/Hearthttp://en.wikipedia.org/wiki/Kidneyhttp://en.wikipedia.org/wiki/Chickenhttp://en.wikipedia.org/wiki/Beefhttp://en.wikipedia.org/wiki/Fishhttp://en.wikipedia.org/wiki/Tunahttp://en.wikipedia.org/wiki/Salmonhttp://en.wikipedia.org/wiki/Milkhttp://en.wikipedia.org/wiki/Egg_(food)http://en.wikipedia.org/wiki/Leaf_vegetablehttp://en.wikipedia.org/wiki/Leaf_vegetablehttp://en.wikipedia.org/wiki/Broccolihttp://en.wikipedia.org/wiki/Tomatohttp://en.wikipedia.org/wiki/Carrothttp://en.wikipedia.org/wiki/Date_palmhttp://en.wikipedia.org/wiki/Sweet_potatoehttp://en.wikipedia.org/wiki/Asparagushttp://en.wikipedia.org/wiki/Avocadohttp://en.wikipedia.org/wiki/G_protein-coupled_receptorhttp://en.wikipedia.org/wiki/Niacin#cite_note-pmid16018973-24http://en.wikipedia.org/wiki/Gi_alpha_subunithttp://en.wikipedia.org/wiki/Gi_alpha_subunithttp://en.wikipedia.org/wiki/Niacin#cite_note-pmid15580557-25http://en.wikipedia.org/w/index.php?title=Niacin&action=edit&section=11http://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Fruitshttp://en.wikipedia.org/wiki/Vegetableshttp://en.wikipedia.org/wiki/Seedshttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Liverhttp://en.wikipedia.org/wiki/Hearthttp://en.wikipedia.org/wiki/Kidneyhttp://en.wikipedia.org/wiki/Chickenhttp://en.wikipedia.org/wiki/Beefhttp://en.wikipedia.org/wiki/Fishhttp://en.wikipedia.org/wiki/Tunahttp://en.wikipedia.org/wiki/Salmonhttp://en.wikipedia.org/wiki/Milkhttp://en.wikipedia.org/wiki/Egg_(food)http://en.wikipedia.org/wiki/Leaf_vegetablehttp://en.wikipedia.org/wiki/Leaf_vegetablehttp://en.wikipedia.org/wiki/Broccolihttp://en.wikipedia.org/wiki/Tomatohttp://en.wikipedia.org/wiki/Carrothttp://en.wikipedia.org/wiki/Date_palmhttp://en.wikipedia.org/wiki/Sweet_potatoehttp://en.wikipedia.org/wiki/Asparagushttp://en.wikipedia.org/wiki/Avocado

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