NIACIN (VITAMIN B3) & BIOTIN

082012100063 082012100067 082012100071 082012100075

OBJECTIVE

To learn the chemistry of Niacin & Biotin.

To find out the dietary sources of Niacin & Biotin.

To know the recommended dietary allowance of Niacin & Biotin.

To identify the coenzyme form & functions of Niacin and Biotin.

To know the deficiency manifestations of Niacin & Biotin.

INTRODUCTION NIACIN IS A WATER-SOLUBLE VITAMIN

ALSO KNOWN AS VITAMIN B3 OR NICOTINIC ACID.

NIACINAMIDE @ NICOTINAMIDE IS THE ACTIVE FORM OF

THIS VITAMIN , FOUND IN TISSUE.

NAD+ AND NADP+ ARE THE COENZYME FORMS OF

NIACIN.

CHEMISTRY OF NIACIN

NIACIN IS PYRIDINE-3-CARBOXYLIC ACID.

NIACINAMIDE IS ACID AMIDE.

ADENINE MONONUCLEOTIDE + NICOTINAMIDE MONONUCLEOTIDE NICOTINAMIDE ADENINE DINUCLEOTIDE (NAD+)

DIETARY SOURCES 60MG OF TRYPTOPHAN YIELD 1MG NIACIN

RECOMMENDED DAILY ALLOWANCE

NORMAL REQUIREMENT :

-ADULT: 20 mg/DAY

-CHILDREN: 15 mg/DAY

LACTATION ADDITIONAL 5MG ARE REQUIRED.

FUNCTIONS: THERAPEUTIC USE :

-NICOTINIC ACID INHIBITS THE FLUX OF FREE FATTY

ACIDS FROM ADIPOSE TISSUE.

-SO ACETYL COA POOL IS REDUCED , HENCE SERUM

CHOLESTEROL IS LOWERED.

NAD+ IS CRUCIAL FOR NAD+ DEPENDENT ENZYMES

eg: lactate dehydrogenase (lactate pyruvate)

NADP+ WILL BE CONVERTED INTO NADPH FOR REDUCTIVE BIOSYNTHETIC REACTION.

eg: HMG CoA reductase (HMG CoA Mevalonate)

NIACIN DEFICIENCY PELLAGRA - is an italian word meaning “rough skin”. a) dermatitis : -in early stage => bright red erythema -Increased pigmentation around neck is known as Casal’s necklace. -Precipitated by exposure to sunlight. b) diarrhea : -May lead to weight loss -Nausea and vomiting may also be present.

C) dementia :- Frequently seen in chronic cases.- Delerium is common in acute pellagra.- Irritability, inability to concentrate and poor memory.- Ataxia and spasticity also seen.

BIOTIN

A.K.A. anti-egg white injury factor, vitamin H. Co-enzyme for carboxylation enzymes

CHEMISTRY

Imidazole ring fused with thiophene ring with a valeric acid side chain.

SOURCES

Normal bacterial flora of the gut Liver Yeast Peanut Soybean Milk Egg yolk REQUIREMENT: 200-300mg

FUNCTION

BIOTIN DEPENDENT ENZYMES Acetyl CoA carboxylase : Acetyl CoA + CO₂ + ATP Malonyl CoA + ADP + Pi Propionyl CoA carboxylase Pyruvate carboxylase

BIOTIN INDEPENDENT REACTIONS Carbamoyl phosphate synthetase Addition of CO2 to form C6 in purine ring Malic enzyme which convert pyruvate to malate

ANTAGONISTS

AVIDINo Protein in egg white has high affinity to biotino Heat labile, boiling of egg neutralize the inhibitory

activityo Can combine with four molecules of biotino Avidin-biotin system – utilized for detection of pathogens

of ELISA testo Enzyme-linked immunosorbent assay (ELISA) is a test

that uses antibodies and color change to identify a substance

DEFICIENCY

Prolonged use of antibacterial drugs SYMPTOMS-Dermatitis-Atrophic glossitis : smooth tongue that is painful-Hyperesthesia : abnormal increase in sensitivity to stimuli-Muscle pain-Anorexia-Hallucinations-Injection of 100-300mg biotin :rapid cure

CONCLUSION

Consuming niacin 20 mg/day can reduce serum cholesterol level.

Many enzymatic reactions in our body depends on coenzyme of niacin (NAD+ and NADP+)

Biotin is crucial for some enzymatic activity that involves carboxylation.

Eating excessive raw egg white can lead to biotin deficiency.

REFERENCE

Textbook of Biochemistry for Medical Students, DM Vasudevan, 6th edition.

Biochemistry, U. Satyanarayana,