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B6 6 pp - Vitamin B6 Spring 2011 2011 Pages 264-269...

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Vitamin B6 Spring 2011 Pages 264-269 Vitamin B 6 : History • First identified rats: 1930’s –antidermatitis, antianemia factor • Deficiency & convulsive seizures infants 1950’s Heat Treated Experimental Human Infant B6 Deficiency • Experimental B6 deficiency infants – deprived of B6 in formula for purpose of documenting clinical symptoms and response to therapy. • Unethical human experimentation. • Parents of infants not fully informed. Experimental B6 Deficiency Infants Deprived of B6 B6 •Structurally-related compounds •Pyridoxine: alcohol (PN) Vitamin B 6 : Chemistry •Pyridoxal: aldehyde (PL) •Pyridoxamine: amine (PM) •5’-phosphate derivatives of above Fig. 9-35, p. 364
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Vitamin B6 Stability • Light sensitive • Heat sensitive –particularly pyridoxal-P Vitamin B6 Stability –pyridoxine-HCL more stable •used in foods that are heat processed –pasteurized infant formulas –major form in supplements and fortified foods Vitamin B6 Food Sources Best-M eat (0.3 mg / 3 oz) white-meat chicken, turkey, fish •Fruits & vegetables (~0.8 mg/serving) • nuts • beans • banana • Fortified products • ready-to-eat cereal Vitamin B 6 : Absorption • Small intestine • Passive diffusion, nonsaturable • Alkaline phosphatase dephosphorylates PLP – free vitamin enters enterocyte • rephosphorylated with ATP and pyridoxal kinase inside cell • Bioavailability – Mixed diet: 75% – Supplement: >90% Transport •Transport: albumin –mainly PLP mainly PLP –Pyridoxal phosphate (PLP) •Coenzyme form Vitamin B 6 : Metabolism •Pyridoxine oxidase required to convert other forms to PLP –FAD dependent enzyme
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Fig. 9-36, p. 364 Vitamin B 6 : Storage & Excretion • Body store: 60-170 mg –80-90% in muscle –Bound to phosphorylase –Overall body half life: ~25 days Vitamin B 6 Excretion • Urinary excretion –4-pyridoxic acid •primary excretory product •reflects recent dietary intake –may not reflect long-term status >100 reactions: coenzyme PLP • Types of reactions PLP dependent Vitamin B 6 : Functions –Amino acid metabolism •transamination •deamination –Hormone & neurotransmittor •decarboxylation Transamination • Catabolism of nearly all amino acids involves –transfer of their amino groups to - keto acids. • Major amino group acceptors are -ketoglutarate and pyruvate • Transamination initally –generate the keto acid of the i id d PMP Transamination amino acid and PMP • Reversal of reaction using - ketoglutarate and pyruvate – generates glutamate or alanine
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Transamination α -ENZ PLP first forms a Schiff base with enzyme and then with amino acid a conjugated double bond system extends from the -carbon of the amine (amino acid) to the nitrogen in PLP
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