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Description
(PYRIDOXINE)
DESCRIPTION
Vitamin B-6 (Pyridoxine) is a component of
the water-soluble vitamin B-complex vitamins. It is composed of three closely
related chemical compounds: pyridoxine, pyridoxal, and pyridoxamine. These
three compounds are metabolically and functionally interrelated and are readily
interconverted.
Vitamin B-6 is involved in protein, fat,
and carbohydrate metabolism, and is a component of the molecular configuration
of many enzymes. Vitamin B-6 functions primarily in the reactions involved in
the nonoxidative degradation of amino acids. |
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Method of
Action
Vitamin B-6 is found in cells in the active form as
coenzyme pyridoxal phosphate, as well as in its amino form, pyridoxamine
phosphate.
Vitamin B-6 participates in
transamination. Vitamin B-6 catalyzes the reaction by acting as a carrier of
the amino group. During transamination, pyridoxal phosphate accepts an amino
group from an amino acid, and is subsequently converted to pyridoxamine
phosphate. The amino group is then transferred to a receptor molecule (usually
alpha-keto glutarate), and pyridoxal phosphate is regenerated. Transamination
reactions can occur between any amino acid and a receptive alpha-keto acid.
Other metabolic processes catalyzed by
vitamin B-6 are: deamination; decarboxylation, the removal of carbon dioxide
from amino acids, a necessary step required for the synthesis of
neurotransmitters from certain amino acids; and desulfuration, the transfer of
a sulfur group from methionine to serine in order to form cysteine. All three
processes utilize vitamin B-6 as a carrier compound. Vitamin B-6 is also
involved in the formation of niacin from tryptophan.
Vitamin B-6 is an important enzyme in the
biosynthesis of hemoglobin and in the production of gamma-aminobutyric acid
(GABA) from glutamic acid.
Vitamin B-complex, vitamin B-1, vitamin
B-2, vitamin C, Pantothenic acid, magnesium, potassium, linoleic acid, and
sodium assist in the absorption of vitamin B-6. Absorption is decreased by
tobacco, alcohol, coffee, oral contraceptive, and exposure to radiation; it is
destroyed by cooking. |
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Properties and
Uses
Vitamin B-6 is used to treat anemic
patients when the anemia is due to vitamin B-6 deficiency.
Vitamin B-6 supplements can help correct
the depression, malaise, glucose intolerance and increased tryptophan excretion
in some women using oral contraceptives.
Treatment with large doses of vitamin B-6
may prevent the effects of isoniazid, a chemotherapeutic agent for
tuberculosis. Vitamin B-6 doses may prevent isoniazid from inhibiting the
conversion of glutamic acid, the only amino acid the brain
metabolizes. |
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Consequences
of Deficiency
Deficiency of vitamin B-6 can cause
seizures by inhibiting the synthesis of gamma-aminobutyric acid (GABA). GABA is
a calming chemical and seizures can result if it is present in insufficient
amounts.
Vitamin B-6 deficiency has been shown to
increase urinary oxalate excretion. This represents the body’s inability
to convert glyoxalate to glycine, which is necessary to synthesize glycine and
serine.
Deficiency in vitamin B-6 can be created
by the use of oral contraceptives, with subsequent symptoms including
depression and increased urinary excretion of tryptophan. |
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Recommended
Dietary Allowances
|
RDA for
adults: |
2.0
mg |
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RDA for
children: |
1.2
mg |
|
RDA for
infants |
0.4
mg |
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RDA for
pregnancy: |
2.5
mg |
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RDA for
lactation: |
2.5
mg |
A deficiency of vitamin B-6 is unlikely in
the presence of generally good diet. However women taking oral contraceptives
may end up with a deficiency in spite of having at least the RDA in the daily
dietary input. This is true of several other drugs also. Since pyridoxine is
involved in amino acid metabolism, the need for pyridoxine varies with dietary
protein intake. For adults, approximately one mg daily is minimal. The RDA
standard is two milligrams per day for adults to ensure a safety margin for
variances in individual need. However this safety margin is eliminated rapidly
in the contest with a number of pharmaceutical drugs. |
