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. 2013 Jul 21;6(Suppl 1):3-8.
doi: 10.4137/IJTR.S11588. Print 2013.

Nutritional aspect of tryptophan metabolism

Tsutomu Fukuwatari  1 , Katsumi Shibata
Affiliations

Nutritional aspect of tryptophan metabolism

Tsutomu Fukuwatari et al. Int J Tryptophan Res. .

Abstract

Mammals, including humans, can synthesize the vitamin nicotinamide from tryptophan in the liver. The resultant nicotinamide is distributed to non-hepatic tissues. We have studied the effects of changes in tryptophan-nicotinamide metabolism on niacin nutritional status. The liver plays a critical role in nicotinamide supply. Animal studies showed that the tryptophan-nicotinamide pathway is affected by physiological conditions, the presence of disease, nutrients, hormones, and chemicals. Human studies have shown that 1 mg of nicotinamide is produced from 67 mg of tryptophan intake, and that the conversion ratio of tryptophan to nicotinamide is enhanced from mid to late pregnancy. These findings have contributed to the determination of dietary reference intakes for niacin recommended in the Dietary Reference Intakes for Japanese 2010. Our findings suggest that the conversion of nicotinamide from tryptophan is important in maintaining niacin nutrition.

Keywords: nicotinamide; nutrition; tryptophan.

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Figures

Figure 1
Figure 1
The tryptophan-nicotinamide pathway. Notes: The pathway consists of the two parts: the first part is from tryptophan to quinolinic acid, and the second is from quinolinic acid to 2-Py and 4-Py, which includes the NAD cycle and the nicotinamide catabolism. Abbreviations: NaMN, nicotinic acid mononucleotide; NMN, nicotinamide mononucleotide; MNA, N1-methylnicotinamide; 2-Py, N1-methyl-2- pridone-5-carboxamide; 4-Py, N1-methyl-4-pridone-3-carboxamide.
Figure 2
Figure 2
Schematic representation of tryptophan dynamics and nicotinamide supply in the tryptophan-nicotinamide pathway. Abbreviations: NaMN, nicotinic acid mononucleotide; NMN, nicotinamide mononucleotide; MNA, N1-methylnicotinamide; 2-Py, N1-methyl- 2-pridone-5-carboxamide; 4-Py, N1-methyl-4-pridone-3-carboxamide.
See this image and copyright information in PMC

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