HUN 4221 Folate 2011 3-pg

HUN 4221 Folate 2011 3-pg - HUN 4221 FOLATE Sp 2011 Folate...

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1 HUN 4221 FOLATE Sp 2011 Folate as Folic Acid or Natural Food Folate Folic Acid Folic acid: - supplements - fortified foods (enriched products)
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2 Folic Acid and Dietary Folate Equivalents: Fortified Foods Foods Average Serving Folic Acid (μg/avg serving) Folate ( g DFE/serving) Macaroni 1 cup 92 167 Enriched White Rice 1 cup 87 153 Bagel 3” diameter 66 129 White Bread 2 slices 52 103 Flour Tortilla 8” diameter 42 77 Pretzels 1 oz 40 81 Hamburger/Hotdog Bun 1 whole 36 73 Saltine Crackers 10 crackers 32 64 Biscuit 1 medium 32 58 Pancakes 3 pancakes, 4” diameter 28 64 Fig 9.27 Sources and Amounts of Folic Acid Fortified “Ready-to Eat” Breakfast Cereals Folic Acid- Containing Supplements 100 - 400 μg/serving 400 μg/supplement “Enriched” Cereal Grain Products ~150 μg/day
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3 Food Folate Occurs naturally Concentrated in selected foods Natural Food Sources of Folate Food Average Serving Folate (μg DFE/avg serving) Beef Liver 3 oz 215 Pinto Beans ½ cup 147 Asparagus ½ cup 134 Spinach (boiled) ½ cup 131 Black Beans ½ cup 128 Orange Juice (from concentrate) 1 cup 110 Romaine Lettuce 1 cup 64 Broccoli (raw) 1 cup 50 Orange 3” diameter 48 Peanuts 1 oz 41 Strawberries (whole) 1 cup 35 Glutamate Glutamate Glutamate Glutamate Glutamate Glutamate Glutamate Enzyme Monoglutamate = Folic Acid
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4 Food folate Folic acid Functions the same! Less readily absorbed than folic acid Folate Absorption • Food folate predominately polyglutamate form • Intestinal absorption of food polyglutamate is a two-step process – Hydrolysis of polyglutamates to monoglutamate – Transport of monoglutamate through the intestinal membranes into enterocyte Folate Absorption • Food polyglutamates cleaved in the jejunal brush border by membrane deconjugase enzyme – Glutamate carboxypeptidase II (GCPII) – Acts as an exopeptidase cleaving terminal glutamates • pH optimum is 6.5 – drugs or disease that significantly affect jejunal pH can impair folate absorption
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5 • Following deconjugation to monoglutamate form • Uptake through saturable or non- saturable process Folate Absorption Folate Absorption • Carrier-mediated process-saturable in dietary range of concentration • Specific carriers are transmembrane folate-binding proteins – Reduced folate carrier (RFC) • bi-directional • higher affinity for reduced folates • greatly reduced affinity for folic acid Folate Absorption • Proton-coupled folate transporter (PCFT) – transmembrane uni-directional transport protein – proton coupling allows concentrative transport of folates at acidic pH – Unlike RFC this carrier has similar affinity for reduced folates and folic acid – Appears to play primary role in folate absorption high and similar affinity for folic acid and reduced folates
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6 Folate Absorption • Non-saturable process of folate in supraphysiological/pharmacological range – Without a transporter Glutamate Carboxypeptidase Proton Coupled Folate Transporter Reduced Folate Carrier Effect of Alcohol on Absorption • Chronic alcohol
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This note was uploaded on 12/09/2011 for the course HUN 4445 taught by Professor Sitren during the Spring '08 term at University of Florida.

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HUN 4221 Folate 2011 3-pg - HUN 4221 FOLATE Sp 2011 Folate...

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