Biochemistry/Pharmokinetics of
Vitamin B6
Pyridoxine is water
soluble and stable in heat and acid mediums, while it is unstable in alkaline
solutions and light. Pyridoxine and its vitamers are absorbed in the upper
small intestine by simple diffusion and transported to the liver for
biotransformation into the active coenzyme P5P, which is then exported from the
liver bound to albumin. Uptake into tissue is by extracellular de-phosphorylation,
followed by metabolic trapping intracellularly as P5P.
P5P-dependent enzymes are
involved in the following reactions:
1. decarboxylation of amino
acids to yield amines, many of which are important neurotransmitters and
hormones.
2. transamination of amino
acids to keto-acids, which are then oxidized and used as metabolic fuel.
3. phosphorolytic cleavage of
glycogen (from liver and muscle) to glucose-one-phosphate.
4. formation of alpha
aminolevulinic acid, a precursor to heme.
5. decarboxylation of phosphatidylserine to
phosphatidylethanolamine in phospholipid synthesis.
6. as a co-factor in a
variety of reactions involving side-chain cleavage, including cystathionine
synthase and cystathionase.
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