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ABOUT AUTHOR

GUL MUNEERS/O ABDUL RAZZAQUE

BIOCHEMISTRY

BS PART II

UNIVERSITY OF SINDH

2K10/BCH/23

PROUD TO BE BIOCHEMIST

WE EXPLORE THE SECRETS OF LIFE

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VITAMIN B3

BY GUL MUNEER

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STUDY OBJECTS Names of vitamin Discovery Properties Structure Chemistry Occurrence RDA Biochemical

functions Digestion & absorption Metabolism Assessment Deficiency Toxicity

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NAMES 0F VITAMIN B3

Niacin Niacinamide 0R Nicotinamide Vitamin P OR PP (pellagra

preventive) Pellagra preventive factor Anti black tongue factor Nicotinic acid Vitamin G (after Goldberger’s

death, vitamin B3 was some times called in his honor)

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DISCOVERY

Joseph Goldberger in 1920.

An Austrian-American

physician of the U.S. Public

Health Service.

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PROPERTIES

Niacin is a white crystalline substance. It is soluble in water & ethyl alcohol but is less soluble in

ether & benzene. It is stable in air & heat. Nicotinamide, when pure,

occurs as white needle like crystals.

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STRUCTURE

Niacin (C6H5O2N) is simplest of all the known vitamins. It is

pyridine derivative. N

C O H

O

N H2

O

C

N

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Nicotinic Acid (Plant form)

Nicotinamide (animal form)(reduced form)

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Precursor : Dietary tryptophanThe coenzymes of Niacin (NAD⁺ & NADP⁺) can be synthesized by the essential amino acid tryptophan. The term “Niacin” is used for Nicotinic acid. The amide form of Niacin is known as niacinamide or nicotinamide. The conversion of Niacin to niacinamide takes place in the kidney, brain slices and liver slices.

CHEMISTRY

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The conversion of tryptophan to nicotinic acid in the body takes

place through a series of intermediate steps, which are

represented below:Tryptophan → Kynurenine → 3-

hydroxykynurenine → 3-hydroxyanthranilic acid → …… → Quinolinic acid → Nicotinic acid

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Dietary nicotinamide, niacin and tryptophan contribute to the

synthesis of the coenzymes NAD⁺ and NADP⁺.

Niacin undergoes a series of reactions to produce NAD⁺ and

NADP⁺.60mgs tryptophan=1mg of niacin for

the synthesis of coenzymes.

12Nicotinamide Adenine Dinucleotide

adenine

If Phosphate here ->NADP

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OCCURRENCE Yeast (most abundantly) Liver Salmon Red meat Poultry Vegetables & fruits (poor) whole grains Pulses & peanuts Note: Milk & eggs contain very

little or no Niacin, are good pellagra-preventive foods because of their high content of Tryptophan.

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NiacinSources

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RECOMMENDED DAILY ALLOWANCE (RDA)

Adult (men) 15-20 mg/day Children 10-15mg/day Adult (women) 13-15mg/day

NOTE : One Niacin Equivalent (NE) = 1 mg Niacin or 60 mg of Tryptophan.

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Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning

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BIOCHEMICAL FUNCTIONS

The coenzymes NAD⁺ and NADP⁺ are involved in a variety of “oxidation-reduction reactions”.

A large number of enzymes belonging to the class “oxidoreductase” are dependent on NAD⁺ or NADP⁺.

NAD⁺ and NADP⁺ participate in almost all the metabolisms (carbohydrate, lipid, protein etc).

Involved in electron transport chain to generate ATP.

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Pyruvate + CoA + NAD+ ------> CO2 + acetyl-CoA + NADH + H+

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Functions of Niacin NAD and NADP participates in 200+ reactions in

the body. 2 NAD+ 2NADH + H+

Glucose Pyruvate

NAD+ NADH + H+

Pyruvate Lactate

NAD+ NADH + H+

Isocitrate Alpha-ketogluterate NAD+ NADH + H+ Alpha-ketogluterate Succinyl CoA NAD+ NADH + H+

Malate Oxaloacetate

Electron transport chain

Citric Acid Cycle

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Digestion and Absorption of Dietary Niacin

Coenzyme form in food hydrolysis in small intestine to free

vitamin absorbed in duodenum nicotinic acid protein bound in corn requires alkali treatment (lime) to

release niacin

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Metabolism of B-3 Conversion of free vitamin to

coenzyme in all cells No storage Excesses metabolized in liver

to variety of chemicals Metabolites excreted in urine

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Assessment of B3 Status Urinary excretion of niacin metabolites N-methyl nicotinamide 2-pyridone

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Deficiency of B3

Pellagra commonly referred to as 3 Ds1. Dermatitis

Inflammation of skin

2. Dementia confused, disoriented

3. Diarrhea irritation/inflammation of mucous membranes

4th D − if not treated may lead to Death

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Dermatitis of Pellagra

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Dermatitis Inflammation of skin Found in the areas of the skin exposed to sun light (neck, dorsal part of feet, ankle, face).

Diarrhea Increased frequency and fluidity of the stools, often with blood and mucus. (loose stools) Dementia Degeneration of nervous tissue (weakness of mind) Symptoms include:Anxiety (fear and worry)Irritability (respond or reaction to stimulus)Poor memoryInsomnia (sleeplessness)

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Niacin

Toxicity symptoms Painful flush, hives, and rash (“niacin

flush”) Excessive sweating Blurred vision Liver damage, impaired glucose

tolerance

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THANK YOU

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THE END