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Effect of Diet Restriction on Some Key Enzymes of Tryptophan-NAD Pathway in Rats.

It is known that dietary tryptophan can be converted to nicotinamide nucleotides in the body. Both the level of tryptophan and the energy content of the diet have been shown to influence the efficiency of conversion. The rate at which tryptophan is converted to nicotinamide nucleotides in the body may be expected to be influenced by the activities of the enzymes concerned with the tryptophan-NAD pathway.

Dietary intake of rats was restricted by feeding varying amounts of a 20% protein diet. After 6 weeks of feeding, some key enzymes of the tryptophan and nicotmic acid-NAD pathway, liver nicotinamide nucleotide concentration, and urinary metabolites of tryptophan and nicotinic acid were studied. With an increase in diet restriction, liver tryptophan oxygenase (EC 1.13.1.12) activity increased.

Quinolinate phosphoribosyltransferase (EC 2,4.2.a.) activity, on the other hand, was found to decrease with moderate diet restriction up to 50% restriction, but increased again with more severe diet restriction in rats fed 25% of ad libitum intake. Liver nicotinate phosphoribosyltransferase (EC 2.4.2.11) activity was also observed to decrease with moderate diet restriction and did not further change when the restriction was severe while picolinate carboxylase (EC 4.1.1.45) activity increased significantly only in severe diet restriction. In rats fed 25% of ad libitum intake, urinary quinolinic acid excretion was low whereas N'-methylnicotinamide excretion was elevated.

Alterations in the enzyme activities accompanied by changes in the levels of urinary metabolites, observed in the present study, suggest that the potential efficiency of conversion of tryptophan to nicotinamide nucleotides is not constant and is influenced by dietary intake.

About the Authors

UPPALA SATYANARAYANA AND BAGEPALLI S. NARASINGA RAO (1977) Effect of Diet Restriction on Some Key Enzymes of Tryptophan-NAD Pathway in Rats. J. Nutr. 107: 2213-2218, 1977. National Institute of Nutrition, Indian Council of Medical Research, Jamai-Osmania, Hyderabad-500007, India

Comments

Dr_Abram_Hoffer

  • Posted on 05/16/2010 05:47 pm
This new work with NAD Therapy is very exciting and I think is right on target. It is indeed an energy-metabolic-deficiency (EMD) because in the absence of this coenzyme cycle almost all the reactions in the body run down... I congratulate Theo Verwey and his colleagues for this remarkable advance in using this concept and in using a simple test, the ratio of pyruvate to lactate as a diagnostic measure, to indicate the dose, duration of treatment etc.

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