Role of Vitamin B₆ on Leucine-Induced Metabolic Changes

Abstract

Administration of leucine at 3 % level in the diet has been shown to increase tryptophan oxygenase activity and to decrease kynureninase activity in the liver and to increase quinolinic acid excretion in the urine of rats fed low amounts of vitamin B₆(0.5 µg/g diet). Vitamin B₆ at 3 µg/g of diet was able to reverse the effects of leucine on enzyme activities, but not on quinolinic acid excretion. Isoleucine at 0.2 % level could counteract the leucine effect on kynureninase but not on tryptophan oxygenase. Administration of leucine also decreased the 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the brain. Simultaneous administration of isoleucine could counteract the effects of leucine on brain 5-HT and 5-HIAA partially at low amounts of vitamin B₆but completely at higher levels of vitamin B₆ in the diet.

Letter to the Editor

“…2 (2) We also showed in rats on marginal intakes of pyridoxine, that leucine further aggravated vitamin B6 deficiency as judged by a low-ered kynureninase, a vitamin B6 dependent enzyme. 3 (3) Our group also demonstrated that the decreased activity of enzyme QPRT brought about by leucine feeding is counteracted by higher amounts of vitamin B6 in the diet.4 (4) Leucine amino transferase, an enzyme which is also pyridoxine-dependent was shown to be stimulated both by leucine as well as by higher amounts of vitamin B6 in the diet5 (5) Tryptophan load test in pellagrins indicated vitamin B6 deficiency.6 Our preliminary clinical trials and leucine tolerance studies also indicate that vitamin B6 administration can effectively cure pellagra and also improve leucine tolerance.…”

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

“…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].…”