Vitamin B3- metabolism

VITAMIN B3 (NIACIN)

• Vitamin B3 is also called as Nicotinic acid or nicotinamide.
• Niacin can be synthesized tryptophan (1mg of the niacin formed from 60mg of tryptophan)

Active form of niacin-

1. NAD+ (Nicotinamide Adenine Dinucleotide)
2. NADP+ (Nicotinamide Adenine Dinucleotide Phosphate)

Coenzymes involved in reactions-

1. Oxidoreduction reaction-

i) NAD+ linked dehydrogenases-

• Isocitrate dehydrogenase
• Malate dehydrogenase
• α-ketoglutarate dehydrogenase
• glutamate dehydrogenase
• glyceraldehydes-3- P dehydrogenase
• lactate dehydrogenase
• β-hydroxyl acyl CoA dehydrogenase

ii) NADP+ linked dehydrogenases-

• Glucose-6-P dehydrogenase in HMP shunt pathway

 2. ADP ribosylation

Metabolism & Excretions-

• Nicotinamide excreted in urine are N¹ –methyl nicotinamide and N¹ –methyl 2-pyridone 5-carboxamide (2-pyridine).
• N-methyl nicotinamide metabolized to methylpyridone-2- and 4-carboxamide
• Nicotinic acid conjugated with glycine to form nicotinuric acid
• Nicotinic acid methylated to trignonelline.
• Daily recommended dose – 20mg/day 

Don’t Forget to Solve all the previous Year Question asked on Vitamin B3- metabolism