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Lecture 16

NUTR 3210 Lecture 16: Micronutrient Part 3

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NUTR 3210
David Mutch

Micronutrient Part 3 Micronutrients that act as enzyme cofactors Niacin, Thiamin, Riboflavin, B6, Folate, B12, Biotin, Pantothenic acid Niacin converts carbs, proteins, fats to energy Vitamin B3 Discovered by studying a condition called pellagra in humans and a similar condition called black tongue in dogs o Niacin is the antiblack tongue factor o So, it prevented these diseases o Pellagra is a niacin deficiency High incidence of these conditions (B3 deficiency) in areas where corn is the main dietary staple o This is bc niacin is bound to complex carbs and poorly absorbed Dietary sources: o Most fish, meats, breads and cereals, coffee and tea o In coffee, trigonelline is converted to niacin by heat coffee bean roasting The higher the temperature, the more niacin is generated o About 8.5g of niacin are generated per 100g of coffee This is about 40 of your RDA In animal foods, niacin occurs predominantly as: o Nicotinamide o Nicotinamide adenine dinucleotide (NAD) o Nicotinamide adenine dinucleotide phosphate (NADP) In plant foods, niacin is predominantly found as nicotinic acid (provitamin) Niacin can also be produced in the liver from tryptophan o But only about 160 of Trp is converted to niacin Digestion and Absorption: NAD and NADP must be digested to absorb niacin o NAD and NADP get hydrolyzed in the gut by glycohydrolase to release free nicotinamide Nicotinic acid and nicotinamide are absorbed a bit in the stomach, but mostly in the small intestine via facilitated diffusion In plasma, niacin is found primarily as nicotinamide o Some nicotinamide are bound to plasma proteins Both forms can cross cell membranes by simple diffusion in most tissues, except the kidney and RBC these require carriermediated uptake o Nicotinamide: the primary precursor for NAD synthesis this can occur in all tissues o Nicotinic acid: used for NAD synthesis in the liver only Once NAD or NADP are produced, niacin is essentially trapped within the cell These cofactors are typically found in their reduced forms as: o NADH: main function is to transfer electrons to ETC o NADPH: main function is as a reducing agent in biochemical pathways
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