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Vitamin Mineral B1 Thiamin B2 Riboflavin B3 Niacin RDA Men 1 2 mg day Women 1 1 mg day Pregnancy 1 4 mg day Lactating 1 5 mg day RDA Men 1 3 mg day Women 1 1 mg day Pregnancy 1 4 mg day Lactating 1 6 mg day Food Sources Meat legumes and whole fortified or enriched grain products In supplements found mainly as thiamin hydrochloride or thiamin mononitrate salt Food Sources Especially foods of animal origin milk and milk products main source eggs meat and legumes also RDA Food Sources Bioavailability Bioavailability Up to 95 of riboflavin is absorbed up to maximum of 25 mg RDA Niacin equivalent used to account for provision from tryptophan average US diet usually contains about 900 mg tryptophan daily so this equates to 15 mg niacin Men 16 mg day Women 14 mg day Pregnancy 18 mg day Lactating 17 mg day UL 35 mg day Food Sources Fish tuna halibut meats beef chicken turkey pork enriched and fortified cereals seeds legumes bread products whole grains Bioavailability Found as niacytin high availability or niacinogens very low yield May be synthesized in liver from tryptophan only 3 of trp 1mg niacin from 60 mg tryptophan riboflavin B6 and iron required in some reactions involved in conversion Body Forms Occurs mainly as nicotinamide nucleotides NAD and NADP Storage Forms NAD and NADP trapped in cell NAD concentration usually higher than NADP excess NAD converted back to nicotinamide to transport to other tissues NAD found Body and Storage Forms Riboflavin FMN and FAD Body Content 30 mg Body Forms Storage Forms Body Forms Exists in free form in plants 95 in animal exists in phosphorylated form Storage Forms High concentrations in liver skeletal muscle heart kidney and brain skeletal muscle may contain half of total thiamin Thiaminases catalyze cleavage of thiamin in raw fish Absorption thought to be high Occurs primarily in jejunum with lesser amounts in the duodenum and ileum free thiamin absorbed into intestinal mucosal cells can be active or passive depending on amount present High amounts passive diffusion Low amounts active and sodium dependent Enhancers Cannot be found Inhibitors Cannot be found Transport either in free form bound to albumin or found as thiamine monophosphate 90 found within blood cells Digestion Absorption Enhancers Inhibitors of Absorption Transport Involved in Energy Transformation Synthesis of Pentoses and NADPH Membrane and Nerve Conduction Noncovalently attached riboflavin can be freed by HCl action not all bound riboflavin is hydrolyzed and available for absorption 7 of FAD attached to histidine or cysteine Animal sources better absorbed than plant sources free riboflavin absorbed by saturable energy dependent carrier mechanism primarily in proximal small intestine also through sodium dependent carriers mainly as NAD and NADP found mainly as NADPH NAD and NADP may be hydrolyzed in GI tract by glycohydrolase to release free nicotinamide Can be absorbed in stomach but more so in small intestine small concentrations absorbed by sodium dependent carrier mediated diffusion high concentrations absorbed almost completely by passive diffusion Enhancers Cannot be found Enhancers Cannot be found Inhibitors Cannot be found Converts to FMN on absorption into intestinal cells riboflavin FMN and FAD transported by variety of proteins albumin fibrinogen globulins Flavoproteins and oxidative energy system usage Succinate dehydrogenase FADH2 then electrons into ETC through ubiquitin Fatty acyl CoA dehydrogenase Sphinganine oxidase requires FAD Coenzyme for xanthine oxidase Inhibitors Cannot be found Up to 1 3 nicotinic acid in plasma bound to plasma proteins transport into kidney tubules and red blood cells require a carrier nicotinamide is primary precursor of NAD nicotinic acid may also be used in liver 200 enzymes require NAD and NADP act as hydrogen donors or electron acceptors Also functions as substrate in non redox roles as donor of ADP ribose Tightly bound to apoenzymes and can easily transport hydrogen from one part of cell to another NADH transfers its electrons from metabolic intermediates through electron transport chain making ATP Glycolysis Oxidative decarboxylation of pyruvate Oxidation of acetyl CoA in TCA cycle B oxidation of fatty acids Oxidation of ethanol NADPH acts as reducing agent in pathways such as fatty acid cholesterol steroid synthesis Oxidation of glutamate Regeneration of glutathione vitamin C and thioredoxin Synthesis of deoxyribonucleotides Generated in HMP shunt and by mitochondrial membrane malate aspartate shuttle Excretion Can be degraded by glycohydrolase into nicotinamide and ADP ribose nicotinamide methylated and oxidized in liver into products excreted in urine Assessment Urine metabolite amounts like N methyl nicotinamide test for deficiency Erythrocyte NAD concentrations or NAD NADP ratios Aldehyde oxidase Pyridoxine phosphate oxidase depends on FMN converts PMP and PNP to PLP Synthesize active form of folate Multiple dehydrogenases in choline catabolism Some neurotransmitters require monoamine oxidase Reduction of glutathione Erol and sulfhydryl oxidase forms disulfide bridges Thioredoxin reductase is involved in synthesis of deoxyribonucleotides Excretion Excreted primarily in urine with small amounts in feces riboflavin not bound to protein in plasma filtered by glomerulus and excreted 60 70 excreted intact in urine urinary excretion is noticeable makes your pee yellow orange Assessment Activity of erythrocyte glutathione reductase high NADPH indicates deficiency Cellular riboflavin concentrations and urinary excretion Toxicity Large doses have been seen to treat migraines without side effects Toxicity Deficiency Toxicity Little danger of thiamin toxicity excessive thiamin 100 times recommended amount all at once associated with headaches convulsions cardiac arrhythmia Toxicity Up to 6 g day used to treat hypercholesterolemia significantly lowers total serum cholesterol triglycerides and LDL and increase HDL inhibits lipolysis in adipose Excretion Excess is excreted intact as well as catabolized for urinary excretion Assessment Erythrocyte transketolase activity or thiamin content in blood or urine Excretion Assessment anaphylactic shock Deficiency Beriberi Loss of appetite hypertrophy and altered heart rate apathy confusion decreased short term memory and irritability Dry Predominantly in older adults Chronic low intake More extensive cardiovascular system involvement Cardiomegaly tachycardia right side heart failure peripheral


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FSU HUN 3226 - Lecture notes

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