B6-vitamiin

B6-vitamiin (Püridoksiin)
Üldandmed
Keemiline valem	C8H11NO3
Molaarmass	169,18 g/mol
Vitamiini omadused
Lahustuvus	Vesilahustuv
Soovitav päevakogus (täiskasvanud (mees))	1,3 mg/päevas
(täiskasvanud (naine))	1,3 mg/päevas
maksimaalne päevakogus (täiskasvanud (mees))	100 mg/päevas
maksimaalne päevakogus (täiskasvanud (naine))	100 mg/päevas
Toimet parandavad
vitamiinid ?
Defitsiidi sümptomid
väsimus ärritatavus depressioon veresuhkru taseme langus (insuliinitundlikkuse tõus) dermatiidid käte, jalgade krambid
Üledoosi sümptomid
naha tundlikkushäired allergilised reaktsioonid
Parimad allikad
Veisemaks, sea-, veise- ja kanaliha, riis, pähklid, banaanid, munakollane

Vitamiin B₆ ehk püridoksiin on vesilahustuv vitamiin ja kuulub B-vitamiinide kompleksi. Aktiivseks vormiks on püridoksaalfosfaat (PLP), mis osaleb aminohapete ja süsivesikute ainevahetuses.

Vormid

Vitamiin B₆ omab erinevaid vorme:

• püridoksiin (PN). PN on see vorm, mida manustatakse kui B₆-vitamiini lisandit.
• püridoksiin 5'-fosfaat (PNP)
• püridoksaal (PL)
• püridoksaal 5'-fosfaat (PLP). PLP on metaboolselt aktiivne vorm.
• püridoksamiin (PM)
• püridoksamiin 5'-fosfaat (PMP)

Funktsioonid

Vitamiin B₆ metaboolselt aktiivne vorm püridoksaalfosfaat osaleb makrotoitainete metabolismis, neurotransmitterite, histamiini ja hemoglobiini sünteesis. Pyridoxal phosphate generally serves as a coenzyme for many reactions and can help facilitate decarboxylation, transamination, racemization, elimination, replacement and beta-group interconversion reactions. The liver is the site for vitamin B6 metabolism.

The primary role of vitamin B₆ is to act as a coenzyme to many other enzymes in the body that are involved predominantly in metabolism. This role is performed by the active form, pyridoxal phosphate. This active form is converted from the two other natural forms founds in food: pyridoxal, pyridoxine and pyridoxamine.

Vitamin B₆ is involved in the following metabolic processes:

• amino acid, glucose and lipid metabolism
• neurotransmitter synthesis
• histamine synthesis
• hemoglobin synthesis and function
• gene expression

Amino Acid Metabolism

Pyridoxal phosphate (PLP) is a cofactor in transaminases that can catabolize amino acids. PLP is also an essential component of two enzymes that converts methionine to cysteine via two reactions. Low vitamin B₆ status will result in decreased activity of these enzymes. PLP is also an essential cofactor for enzymes involved in the metabolism of selenomethionine to selenohomocysteine and then from selenohomocysteine to hydrogen selenide. Vitamin B₆ is also required for the conversion of tryptophan to niacin and low vitamin B₆ status will impair this conversion. PLP is also used to create physiologically active amines by decarboxylation of amino acids. Some notable examples of this include: histidine to histamine, tryptophan to serotonin, glutamate to GABA (gamma-aminobutyric acid), and dihydroxyphenylalanine to dopamine.

Pyridoxal phosphate is involved in almost all amino acid metabolism, from synthesis to breakdown.

1. Transamination: transaminase enzymes needed to break down amino acids are dependent on the presence of pyridoxal phosphate. The proper activity of these enzymes are crucial for the process of moving amine groups from one amino acid to another.

2. Transsulfuration: Pyridoxal phosphate is a coenzyme needed for the proper function of the enzymes cystathionine synthase and cystathionase. These enzymes work to transform methionine into cysteine.

3. Selenoamino acid metabolism: Selenomethionine is the primary dietary form of selenium. Pyridoxal phosphate is needed as a cofactor for the enzymes that allow selenium to be used from the dietary form. Pyridoxal phosphate also plays a cofactor role in releasing selenium from selenohomocysteine to produce hydrogen selenide. This hydrogen selenide can then be used to incorporate selenium into selenoproteins.

4. Vitamin B₆ is also required for the conversion of tryptophan to niacin and low vitamin B₆ status will impair this conversion.

Gluconeogenesis

Vitamiin B₆ also plays a role in gluconeogenesis. Pyridoxal phosphate can catalyze transamination reactions that are essential for the providing amino acids as a substrate for gluconeogenesis. Also, vitamin B₆ is a required coenzyme of glycogen phosphorylase, the enzyme that is necessary for glycogenolysis to occur.

Lipid Metabolism

Vitamin B₆ is an essential component of enzymes that facilitate the biosynthesis of sphingolipids. Particularly, the synthesis of ceramide requires PLP. In this reaction serine is decarboxylated and combined with palmitoyl-CoA to form sphinganine which is combined with a fatty acyl CoA to form dihydroceramide. Dihydroceramide is then further desaturated to form ceramide. In addition, the breakdown of sphingolipids is also dependent on vitamin B₆ since S1P Lyase, the enzyme responsible for breaking down sphingosine-1-phosphate, is also PLP dependent.

Manustamine sportlastel

RDA:

• vastupidavusalad 2-6 mg
• jõuspordialad 4-12 mg

Vaata ka

• Vitamiinid
• Rasvlahustuvad vitamiinid
• Vesilahustuvad vitamiinid