Leucine Leveling effect

These three compounds exert many similar effects in nucleotide metabolism of chicks and rats [167]. They cause an increase of the liver RNA content and of the nucleotide content of the acid-soluble fraction in chicks [168], as well as an increase in rate of turnover of these polynucleotide structures [169,170]. Further experiments in chicks indicate that orotic acid, vitamin B12 and methionine exert a certain action on the activity of liver deoxyribonuclease, but have no effect on ribonuclease. Their effect is believed to be on the biosynthetic process rather than on catabolism [171]. Both orotic acid and vitamin Bu increase the levels of dihydrofolate reductase (EC 1.5.1.4), formyltetrahydrofolate synthetase and serine hydroxymethyl transferase in the chicken liver when added in diet. It is believed that orotic acid may act directly on the enzymes involved in the synthesis and interconversion of one-carbon folic acid derivatives [172]. The protein incorporation of serine, but not of leucine or methionine, is increased in the presence of either orotic acid or vitamin B12 [173]. In addition, these two compounds also exert a similar effect on the increased formate incorporation into the RNA of liver cell fractions in chicks [174—176]. It is therefore postulated that there may be a common role of orotic acid and vitamin Bj2 at the level of the transcription process in m-RNA biosynthesis [174—176]. 

People can suffer from a variety of inborn metabolic errors that can result in various amino acids exhibiting toxic effects if ingested above certain threshold levels. Specialty products, intended to be absent these amino acids, must be rigorously tested for verification that threshold levels are not exceeded. Examples of this situation include phenylketoneuria (intolerance of phenylalanine) and maple syrup urine disease (intolerance for leucine, isoleucine, and valine). 

The decarboxylation of 3-carboxybenzisoxazole (225 R = H, NO2) gives CO2 and (226). This reaction has been studied using 13C and 15N kinetic isotope effects.201 The isotope effects were modelled theoretically at the semiempirical and ab initio levels, but comparison of experimental and theoretical results shows that die former cannot be successfidly predicted by theory at the level of calculation employed. The kinetics of decarboxylation and deamination of DL-leucine by acidic permanganate in die presence of silver ion in moderately concentrated sulfuric acid is a two-stage process.202 The... 

The pharmacological effect of L-dopa is affected by diet (362). The off period in Parkinsonian patients treated with L-dopa is a clinical problem, since the efficacy of the drug suddenly fails. Because of the inverse relationship between the plasma levels of large neutral amino acid (LNAA) and the clinical performance of Parkinsonian patients (362) and the fact that the transcellular transport of L-leucine is inhibited by L-dopa (363) across primary cultured bovine brain capillary endothelial cells, the off period may be attributed to the membrane transport of L-dopa via LNAAT at the BBB. In addition to L-dopa, baclofen and melphalan are suggested to be taken up into the brain via amino acid transporter (363,364), and thereby, their brain transport might be also affected by the plasma concentration of large neutral amino acids. 

Additions of valine, leucine, and isoleucine were found to relieve the growth inhibitory effects of TP on Bacillus cell cultures, soybean cell cultures, and Arabidopsis seedlings. ALS isolated from a number of sources was found to be sensitive to TP at nM levels. The barley enzyme has been amenable to purification. A purification procedure that gives >60 % recovery and 235-fold purification is described. 

Manson JA and Carpenter KJ (1978a) The effect of a high level of dietary leucine on the niacin status of chicks and rats. Journal of Nutrition 108,1883-8. 

Similar results have been reported for polymorphisms at amino acid 55, with the PONl paraoxonase activity in blood serum from 55M (methionine) homozygotes reduced compared to either the 55L (leucine) homozygotes or the LM heterozygotes (Mackness et al, 1997). While it is intuitive that the rate of detoxification of a substrate would be dependent on the expression levels of these endogenous enzymes, the effects of the genetic polymorphisms suggest that catalytic efficiency is an equally important consideration. 

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