Effect of leucine at different levels of pyridoxine on hepatic quinolinate phosphoribosyl transferase (EC2.4.2.19) and leucine aminotransferase (EC2.6.1.6) in rats

Abstract

1. Effects of incorporating 30 g leucine/kg into diets on quinolinate phosphoribosyl transferase (QPRT; EC 2.4.2.19) activity and leucine aminotransferase (EC 2.6.1.6) activity were studied in groups of rats receiving 5, 30 and 60 micrograms of pyridoxine/10 g diet. 2. The results indicated that 30 g leucine/kg diet significantly reduced the QPRT activity when the diets provided 5 micrograms pyridoxine/10 g and that the effect was only marginal when the diet included 30 micrograms pyridoxine/10 g. The inhibitory effect was completely absent when the diet provided higher amounts of pyridoxine (60 microgram/10 g). 3. These results suggest that additional amounts of pyridoxine are necessary to counteract the effects of excess of leucine in the diet. 4. Leucine aminotransferase activity was increased in rats given diets containing higher amounts of pyridoxine; supplementary leucine also increased the enzyme activity.

Role of Nicotinamide Adenine Dinucleotide and Related Precursors as Therapeutic Targets for Age-Related Degenerative Diseases: Rationale, Biochemistry, Pharmacokinetics, and Outcomes

“…It may also be due to the rate-limiting action of cosubstrate-dependent quinolinic acid phosphoribosyltransferase (QPRT) (267,304). Excess amino acid leucine inhibits QPRT, which prevents the formation of niacin or NA to nicotinic acid mononucleotide (NAMN) (189). Reduced tryptophan availability, particularly after chronic immune activation or in the absence of a tryptophan-rich diet (i.e., soy, meat, fish, eggs, and peanuts), may also be associated with the development of pellagra (217).…”

Effect of Dietary Restriction with and without Excess Leucine on Hepatic Tryptophan Oxygenase, 3-Hydroxyanthranilate Oxygenase and Leucine Aminotransferase in Rats

“…In the case of 3-hydroxyanthranilate oxy genase, however, induction was seen only when excess leucine was fed with 50% re striction of the ad libitum intake of food. From the present work it therefore appears that the effect of undemutrition and excess leucine in inducing the above enzymes is additive, since excess leucine is known to induce tryptophan oxygenase and leucine aminotransferase [Ghafoorunissa and Rao, 1973;Krishnaswami and Rao, 1978]. Excess leucine with severe dietary restriction (25% ad libitum intake) seems to repress the activ ities of all three enzymes as shown in ta ble III.…”

“…With excess dietary leucine the levels of tryptophan oxygenase and picolinate carboxylase are increased, whereas qui nolinic phosphoribosyl transferase activity is decreased [Ghafoorunissa and Rao, 1973;Rao et al, 1975]. Dietary leucine is also known to induce leucine aminotransferase [Krishnaswami and Rao, 1978]. Undemutri tion produced by restricting the diet has been reported to increase the levels of tryptophan oxygenase [Salyanarayana and Rao, 1977a].…”

Impact of NAD+ metabolism on ovarian aging

“…The enzyme responsible for de novo NAD synthesis is predominantly expressed in the liver and kidney [ 158 – 161 ]. De novo synthesis is also called the kynurenine pathway, which begins with complex reactions converting tryptophan into quinolinic acid (QA) and then producing nicotinic acid mononucleotide (NAMN) from QA and 5-phosphoribosyl-1-pyrophosphate (PRPP) via the catalytic action of quinolinic acid phosphoribosyltransferase (QaPRT) [ 162 ]. NAMN can also be synthesized via the Preiss-Handler pathway, which utilizes vitamin B3 [ 163 ].…”