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NUTR 3330 (14)


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NUTR 3330
Alison Duncan

VITAMIN B6 PYRIDOXINE - 6 related compounds: pyridoxal, pyridoxine, pyridoxamine and their phosphates - phosphorylated in foods: phosphate removed by intestinal enzymes - well absorbed passively - taken up by tissues and re-phosphorylated - major metabolite, 4-pyridoxic acid, excreted in urine CO-ENZYME FORM - pyridoxal phosphate (PLP) - riboflavin needed to convert pyridoxine → PLP - heavily involved in amino acid metabolism METABOLIC ROLE Amino Acid Metabolism - primary role o transamination, R-group conversion (serine/glycine), decarboxylations - many aspects of intermediary metabolism; particularly GNG (gluconeogenesis) - kyurenine pathway = tryptophan metabolism = synthesis of niacin (B ) 3 Schiff Base - vitamin B 6alling card - allows PLP to effectively facilitate amino acid metabolism - PLP binds to enzyme between PLP aldehyde group and enzyme amino group o forms imine group H R-C=N-R Nervous System - synthesis of neurotransmitters (requires PLP dependent enzymes) - examples: serotonin, dopamine, GABA - tryptophan → serotonin - vitamin B 6eficiency = neurological problems – infant formula did not have enough B which6 caused seizures in infants Hormone function - PLP binds to steroid hormone receptors (on plasma membrane in cytosol and on nucleus) o inhibits binding of hormones, decreases effects o steroid responsiveness lower in B s6fficient versus deficient animals o can modulate steroid hormone Glycogen Breakdown - PLP involved in glycogenolysis (glycogen → glucose) o coenzyme for glycogen phosphorylase VITAMIN B6 PYRIDOXINE Red Blood Cell Formation and Function - PLP acts as coenzyme involved in synthesis of heme - Pyridoxal (PL) and PLP able to bind to Hb o affects ability to pick up and release O 2 o impact on normal oxygen delivery to tissues is not known Immune function - not clear - likely related to PLP role as coenzyme for enzymes involved in mobilization of single-carbon functional groups o one-carbon metabolism/transfer of one carbon unit o serine/glycine interconversion – serine OH-methyltransferase - synthesis of nucleic acids - B 6eficiency = IL-2 = decreased lymphocyte proliferation ASSESSING VITAMIN B STAT6S Load Tests (want to max out
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