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PubMed1984

Heterogeneity of free valine pools for protein synthesis on free and membrane-bound polysomes in rat liver.

When rat liver was pulse-labeled with [3H]valine in vivo, the nascent peptide on membrane-bound polysomes was found to be more highly labeled than that on free polysomes. Nascent peptides were purified from both classes of polysomes and, after hydrolysis, the amino acids were reacted with 14C-labeled 1-fluoro-2,4-dinitrobenzene. The specific activity of [3H]valine was determined from the [14C]-dinitrophenyl-[3H]valine after purification by two-dimensional thin layer chromatography. With this approach we found that the specific activity of [3H]valine in the nascent peptide of membrane-bound polysomes was more than twice that of free polysomes. Moreover, when rats were pretreated with a lysosomal protease inhibitor, the differences between the specific activities of valine in nascent peptides of the two classes of polysomes tended to decrease. Our results indicate the existence of two distinct pools for valine used for protein synthesis in liver cells; one serves as a precursor for the synthesis of secretory proteins on membrane-bound polysomes and the other as a precursor for the synthesis of intracellular proteins on free polysomes.

Animals↗
PubMed2003

Interactions of various supplies of isoleucine, valine, leucine and tryptophan on the performance of laying hens.

The present study was undertaken to investigate the interactions among the supplies of isoleucine, leucine, valine, and tryptophan in laying hens. A three-factor trial was conducted with laying hens in which the dietary concentrations of isoleucine (5.7, 8.0, and 11.5 g/kg), valine and leucine (6.3 and 7.2 g/kg and 10.1 and 11.5 g/kg, respectively), and tryptophan (1.5 and 2.4 g/kg) were varied. At the lowest concentration of valine + leucine, an increase in dietary isoleucine concentration led to a dose-dependent reduction in feed consumption, daily egg mass, and body weight gain and an increase of the isoleucine concentration in plasma. At a high dietary concentration of valine + leucine, excess dietary isoleucine concentration caused only a weak depression of performance parameters; the isoleucine concentration in plasma was independent of the dietary isoleucine concentration. Increasing the dietary tryptophan concentration did not influence the effect of an excessive dietary isoleucine concentration on performance parameters. Increasing the tryptophan concentration from 1.5 to 2.4 g/kg diet did, however, lead to a significant increase in feed consumption, irrespective of the supply of isoleucine, valine, and leucine. In conclusion, our study demonstrates that the supply of valine + leucine influenced the effects of excess dietary isoleucine in laying hens, whereas the supply with tryptophan did not.

Amino Acids↗
PubMed2005

Feedback-resistant acetohydroxy acid synthase increases valine production in Corynebacterium glutamicum.

Acetohydroxy acid synthase (AHAS), which catalyzes the key reactions in the biosynthesis pathways of branched-chain amino acids (valine, isoleucine, and leucine), is regulated by the end products of these pathways. The whole Corynebacterium glutamicum ilvBNC operon, coding for acetohydroxy acid synthase (ilvBN) and aceto hydroxy acid isomeroreductase (ilvC), was cloned in the newly constructed Escherichia coli-C. glutamicum shuttle vector pECKA (5.4 kb, Km(r)). By using site-directed mutagenesis, one to three amino acid alterations (mutations M8, M11, and M13) were introduced into the small (regulatory) AHAS subunit encoded by ilvN. The activity of AHAS and its inhibition by valine, isoleucine, and leucine were measured in strains carrying the ilvBNC operon with mutations on the plasmid or the ilvNM13 mutation within the chromosome. The enzyme containing the M13 mutation was feedback resistant to all three amino acids. Different combinations of branched-chain amino acids did not inhibit wild-type AHAS to a greater extent than was measured in the presence of 5 mM valine alone (about 57%). We infer from these results that there is a single binding (allosteric) site for all three amino acids in the enzyme molecule. The strains carrying the ilvNM13 mutation in the chromosome produced more valine than their wild-type counterparts. The plasmid-free C. glutamicum DeltailvA DeltapanB ilvNM13 strain formed 90 mM valine within 48 h of cultivation in minimal medium. The same strain harboring the plasmid pECKAilvBNC produced as much as 130 mM valine under the same conditions.

Acetolactate Synthase↗
PubMed1971

Valine accumulation by alpha-aminobutyric acid-resistant mutants of Serratia marcescens.

alpha-Aminobutyric acid, norvaline, and norleucine, which are analogues of branched-chain amino acids, inhibited the growth of Serratia marcescens. The inhibitory effect of these three analogues was counteracted by branched-chain amino acids. A number of mutants resistant to these analogues were isolated. alpha-Aminobutyric acid-resistant (abu-r) mutants markedly accumulated l-valine in the culture medium, but the other analogue-resistant mutants did not. Acetohydroxy acid synthetase, which seems to be rate-limiting for the biosynthesis of l-valine, was derepressed in abu-r mutants. One of the abu-r mutants, no. 140, which accumulated over 8 mg of l-valine per ml, had about a 20-fold increase in the enzyme level. Most of the abu-r mutants had acetohydroxy acid synthetase activity which was sensitive to feedback inhibition by l-valine to the same extent as in the parent strain. However, the enzyme of two of abu-r mutants was less sensitive to l-valine, and one of the two was the best valine accumulator.

Aminobutyrates↗
PubMed1978

Suppressors of a genetic regulatory mutation affecting isoleucine-valine biosynthesis in Escherichia coli K-12.

Escherichia coli K-12 mutant PS187 carries a mutation, ilvA538, in the structural gene for the biosynthetic L-threonine deaminase that leads to a leucine-sensitive growth phenotype, an isoleucine- and leucine-hypersensitive L-threonine deaminase, and pleiotropic effects resulting in abnormally low and invariant expression of some of the isoleucine-valine biosynthetic enzymes. Fifty-eight derivatives of strain PS187 were isolated as resistant to growth inhibition by leucine, by valine, or by valine plus glycly-valine and were biochemically, genetically, and physiologically characterized. All of these derivatives produced the feedback-hypersensitive L-threonine deaminase, and thus presumably possess the ilvA538 allele of the parent strain. Elevated synthesis of L-threonine deaminase was observed in 41 of the 58 isolates. Among 18 strains analyzed genetically, only those with mutations linked to the ilv gene clusters at 83 min produced elevated levels of L-threonine deaminase. One of the strains, MSR91, isolated as resistant to valine plus glycyl-valine, was chosen for more detailed study. The locus in strain MSR91 conferring resistance was located in four factor crosses between ilvE and rbs, and is in or near the ilvO gene postulated to be a site controlling the expression of the ilvEDA genes. Synthesis of the ilvEDA gene products in strain MSR91 is constitutive and derepressed approximately 200-fold relative to the parent strain, indicating that the genetic regulatory effects of the ilvA538 allele have been suppressed. Strain MSR91 should be suitable for use in purification of the ilvA538 gene product, since enzyme synthesis is fully derepressed and the suppressor mutation is clearly not located within the ilvA gene.

Chromosome Mapping↗
PubMed1982

Interconversion of valine and leucine by Clostridium sporogenes.

Clostridium sporogenes has been found to require L-leucine and L-valine for growth in a minimal medium, although valine can be replaced by isobutyrate and leucine by isovalerate. Cells grown in minimal media incorporated significant 14C from [14C]valine into leucine and from [14C]leucine into valine. Growth with [4,5-3H]leucine also resulted in the incorporation of 3H into valine. These results indicate that these bacteria can interconvert leucine and valine.

Amino Acids↗
PubMed1986

Glucose represses formation of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine and isopenicillin N synthase but not penicillin acyltransferase in Penicillium chrysogenum.

The content of alpha-aminoadipyl-cysteinyl-valine, the first intermediate of the penicillin biosynthetic pathway, decreased when Penicillium chrysogenum was grown in a high concentration of glucose. Glucose repressed the incorporation of [14C]valine into alpha-aminoadipyl-cysteinyl-[14C]valine in vivo. The pool of alpha-aminoadipic acid increased sevenfold in control (lactose-grown) penicillin-producing cultures, coinciding with the phase of rapid penicillin biosynthesis, but this increase was very small in glucose-grown cultures. Glucose stimulated homocitrate synthase and saccharopine dehydrogenase activities in vivo and increased the incorporation of lysine into proteins. These results suggest that glucose stimulates the flux through the lysine biosynthetic pathway, thus preventing alpha-aminoadipic acid accumulation. The repression of alpha-aminoadipyl-cysteinyl-valine synthesis by glucose was not reversed by the addition of alpha-aminoadipic acid, cysteine, or valine. Glucose also repressed isopenicillin N synthase, which converts alpha-aminoadipyl-cysteinyl-valine into isopenicillin N, but did not affect penicillin acyltransferase, the last enzyme of the penicillin biosynthetic pathway.

2-Aminoadipic Acid↗
PubMed1975

Effect of valine on the control of fatty acid synthesis in white adipose tissue of the rat.

In adipocytes from fed rats, the rate of fatty acid synthesis in the presence of glucose and insulin was inhibited 40% by valine (5 mm). tthis inhibition was largely abolished by the addition to the incubation medium of the transaminase inhibitor aminooxy acetate, and of pyruvate and agents which raise the intracellular pyruvate levels such as N,N,N1,N1-tetramethyl-p-phenylenediamine. Pyruvate output into the incubation medium from fat pads obtained from fed rats and incubated with glucose and insulin was decreased significantly by the addition of valine. When adipocytes were incubated under similar conditions, the final concentration of pyruvate in the incubation medium was 42 +/- 1.6 muM under control conditions and approximately one third of this value in the presence of 2.5 mM valine. Valine had no significant effect on pyruvate dehydrogenase (lipoate) (EC 1.2.4.1) activity when assayed in homogenates prepared from adipose tissue previously incubated for 60 min with the amino acid. Although the ketoacid analogue of valine alpha-ketoisovaleric acid, is a competitive inhibitor of pyruvate dehydrogenase (lipoate) (K1 = 1.4 mM), this cannot solely account for the valine-induced reduced rate of lipogenesis. Rather, the mechanism involves a reduction in pyruvate concentration and thereby a diminished flow through pyruvate dehydrogenase (lipoate). Details of the possible mechanism are discussed.

Adipose Tissue↗
PubMed1994

Effect of a flooding dose of leucine in stimulating incorporation of constantly infused valine into albumin.

Recently, we demonstrated increased incorporation of [13C]valine tracer into muscle protein after administration of a flooding dose of L-leucine. We have now investigated the possibility of a similar effect on albumin synthesis in the same group of volunteers. We gave L-[1-13C]leucine (20 atom%, 0.05 g/kg) during the final 90 min of a 7.5-h primed constant infusion of L-[1-13C]valine (99 atom%, 1.5 mg/kg prime constant infusion of 1.5 mg.kg-1.h-1) in healthy male volunteers in the postabsorptive state. Blood samples, taken at 0.5- to 1-h intervals during the constant infusion and at 5- to 30-min intervals during the application of the flooding dose, were analyzed for the concentration and 13C enrichment of leucine, valine, and their ketoacids. Albumin was isolated and hydrolyzed, and the enrichments of incorporated valine and leucine were compared with the mean enrichment of various possible precursor pools to calculate the apparent rate of albumin protein synthesis according to the standard procedures. During constant infusion of [13C]valine tracer the rate of albumin synthesis (measured using alpha-ketoisovalerate labeling as a surrogate for the true precursor) was 0.250 +/- 0.041%h (SD), a value identical to that routinely obtained using constant leucine tracer infusion and alpha-ketoisocaproate labeling. During the application of the flooding dose of leucine, the rate of incorporation of tracer [13C]valine into albumin increased by 73% to 0.433 +/- 0.129%/h (P < 0.05); the apparent protein synthetic rate calculated from the incorporation of leucine applied during the flood was 0.402 +/- 0.057 (P < 0.001). These results raise further doubts about the validity of the flooding dose method for the measurement of rates of human protein synthesis.

Adult↗
PubMed1997

Effects of leucine on whole body leucine, valine, and threonine metabolism in humans.

We tested whether expansion of the plasma leucine pool distorts leucine or valine tracer kinetics, causing errors in the derived values of whole body proteolysis. Seven normal adults received a 10-h primed-continuous tracer infusion of L-[5,5,5-2H3]leucine, L-[(1-13)C]valine, and L-[(1-13)C]threonine, during the final 7 h of which L-leucine was infused at a rate that more than tripled the plasma leucine concentration. Leucine, valine, and threonine rates of appearance were converted to a common value of whole body proteolysis on the basis of their concentrations in body proteins. The conversion of labeled leucine and valine to their corresponding branched-chain alpha-keto and alpha-hydroxy acids was also monitored. Before the unlabeled leucine infusion, postabsorptive whole body proteolysis was estimated similarly by the three tracers (approximately 180 mg protein.kg-1.h-1. The leucine infusion reduced proteolysis by an average of 21% (P < 0.006), as estimated by use of valine or threonine kinetics, and by 10% by use of leucine kinetics (P < 0.02). No delay in the conversion of valine to alpha-ketoisovalerate occurred during the leucine infusion. Thus all three tracers indicated similar postabsorptive rates of whole body proteolysis and a reduction of proteolysis during leucine administration, although the magnitude of the effect was underestimated with use of the leucine tracer.

Adult↗
PubMed1994

Primary culture of salamander intestinal epithelial cells from nests: whole cell Na+ currents induced by valine.

Methods are described for isolating the cell nests, subepithelial clusters of germinative cells, from salamander intestinal mucosa and for growing the nests in culture into polarized monolayers of intestinal epithelial cells. Cells were viable in culture for up to 3 wk. The capacity of the monolayer cells to engage in membrane transport was evaluated using the patch-clamp technique in the whole cell mode. L-Valine (25 mM) induced an inward current in small intestinal cells of 25.8 +/- 5.7 pA and depolarized the cell membrane 14.5 +/- 1.6 mV. L-Alanine and L-phenylalanine were similarly effective, whereas D-valine was ineffective. The Km of the transporter for valine was 90 mM. Replacement of bath Na with tris(hydroxymethyl)aminomethane eliminated the inward current induced by valine. The basal (solute-independent) inward current was also reduced by Na+ replacement. Glucose did not induce a Na+ current. In contrast to the effect of valine on small intestinal cells, large intestinal cells were unresponsive to valine. It is concluded that the cultured small intestinal cells possess Na-amino acid but not Na-sugar cotransport. This profile of behavior is characteristic of undifferentiated small intestinal cells. Primary cultures of salamander small intestinal cells should be useful for studying enterocyte function and the developmental biology of the small intestinal mucosa.

Animals↗
PubMed1995

Effect of valine on 5-HT-mediated prolactin release in healthy volunteers, and on mood in remitted depressed patients.

BACKGROUND: Animal experimental studies suggest that the amino acid valine may decrease brain serotonin (5-HT) function by inhibiting the transport of the 5-HT precursor, L-tryptophan, across the blood barrier. The aim of the present study was to assess whether valine could decrease brain 5-HT function in healthy subjects and provoke symptomatic relapse in recently remitted depressed patients taking antidepressant drug treatment. METHOD: We studied the effect of valine (30 g) on the prolactin (PRL) response to the 5-HT releasing agent, D-fenfluramine, in healthy male subjects and on the mood of 12 remitted depressed patients taking either selective serotonin re-uptake inhibitors (n = 10) or lithium and amitriptyline (n = 2). RESULTS: Valine significantly lowered the PRL response to D-fenfluramine in healthy subjects. In the remitted depressives, valine caused a mild but detectable lowering of mood on a number of measures but only one patient experienced a significant relapse in mood. CONCLUSIONS: Valine administration may decrease brain 5-HT neurotransmission in humans. This effect could explain the mild increase in depressive symptoms in patients taking 5-HT-potentiating drugs.

Adult↗
PubMed1977

Effect of valine on propionate metabolism in control and hyperglycinemic fibroblasts and in rat liver.

Measurement of methylmalonyl-CoA mutase and propionyl-CoA carboxylase activities in lysates from fibroblasts derived from control, nonketotic hyperglycinemia, propionic acidemia, and both vitamin B12-responsive and -nonresponsive variants of methylmalonic acidemia showed only one abnormality: a 59% decrease in carboxylase activity in the nonketotic hyperglycinemic lysates (P less than 0.01). When fibroblasts from all cell types were grown on valine-supplemented (24 mM) media, mutase activity was generally inhibited. As for carboxylase activity, control lines were inhibited 35% as compared to controls without valine and propionic acidemia activity was undetectable. On the other hand, carboxylase activity in both methylmalonic acidemia variants was increased 40% and nonketotic hyperglycinemia carboxylase activity was increased 80% (P less than 0.01) when grown on valine-supplemented media. Isoleucine could not substitute for valine in producing increased carboxylase activity in these mutants. Glycine cleavage activity in fresh rat liver homogenates (11.1 micronmol/gm protein/90 min) did not vary significantly when 24 mM valine was added to the reaction (9.9 micronmol/mg protein/90 min). Therefore, the hyperglycinemia observed in both ketotic and nonketotic forms is probably not caused by a direct effect of valine on the glycine cleavage reaction. These data suggest that the presence of increased amounts of propionic acid in serum or urine does not necessarily rule out the possibility of nonketotic hyperglycinemia due to the decreased activity of the carboxylase enzyme.

Carboxy-Lyases↗
PubMed1984

Influence of basic and branched chain amino acid interactions on the lysine and valine requirements of young turkeys.

Two experiments were conducted to determine the influence of amino acid interactions on the lysine and valine adequacy of a low protein diet fed to Large White turkeys from 7 to 19 days of age. Corn-soybean meal diets containing 22 and 30% protein served as controls in both experiments. Test diets involved supplementation of the 22% protein diet with several essential amino acid mixtures. Each diet was fed ad libitum to two pens of eight males and two pens of eight females in each of three trials, except that the 22% protein control diet was fed to four and two pens of each sex per trial in Experiments 1 and 2, respectively. Experiment 1 varied the levels of lysine (0, .60, and 1.20%) and arginine (0, .64, and 1.28%) included in the amino acid mixture. A decrease in supplemental lysine from .60 to 0% reduced weight gain and feed efficiency by 8.6 and 2.4%, respectively. The lysine deficiency was not exacerbated by arginine supplementation up to 179% of the requirement. The effects of altering the leucine (0, .54, and 1.08%) and isoleucine (0 and .4%) contents of the amino acid mixture on the valine requirement were investigated in Experiment 2. Leucine and isoleucine supplementation of diets containing 1.25% valine acted independently to reduce weight gain and feed intake, but the depressions were reversed with the addition of .44% valine. Maximum weight gain and feed efficiency were not achieved with diets containing 1.25% valine and no added leucine or isoleucine, which were indicative of a true valine deficiency in the basal 22% protein diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1977

Codon-acticodon recognition in the valine codon family.

An in vitro protein-synthesizing system completely dependent on added valine tRNA (valyl-tRNAval) and programmed with RNA from the phage MS2 has been used to investigate the incorporation into MS2 coat protein of valine from isoaccepting valyl-tRNAsval with the anticodons U AC (U represents 5-oxyacetic acid uridine monophosphate), GAC, and IAC in response to the four valine codons GUU, GUC, GUA, and GUG. By examining the incorporation of valine into NH2-terminal and internal positions of three tryptic peptides from the MS2 coat protein it has been established that these anticodons each recognize all four valine codons. We therefore conclude that under our conditions of in vitro protein synthesis the genetic code, as far as the valine codons are concerned, is operationally a two letter code, i.e. the third codon nucleotide has no absolute discriminating function.

Amino Acid Sequence↗
PubMed1984

Oral administration of alpha-ketoisovaleric acid or valine in humans: blood kinetics and biochemical effects.

alpha-Ketoisovaleric acid levels increase from 10.6 +/- 0.8 to 121 +/- 20 mumol/L, and valine levels increase from 175 +/- 14 to 940 +/- 50 mumol/L after oral administration of an isomolar (62.5 mg/kg) bolus of alpha-ketoisovaleric acid or valine to healthy human subjects. alpha-Ketoisovaleric acid levels have a different time course relative to valine. alpha-Ketoisovaleric acid and valine affect various other amino and keto acids, and some of these effects are qualitatively different. alpha-Ketoisovaleric acid enhances alpha-ketoisocaproic acid and alpha-keto-beta-methyl-n-valeric acid, but diminishes the corresponding amino acids, and causes an early decline of ornithine along with a late augmentation of plasma arginine. Valine does the opposite. The data suggest that in humans, overall capacity for alpha-ketoisovaleric acid decarboxylation appears greater than the capacity for valine transamination, and that all branched-chain amino acids and branched-chain keto acids seem to be interconvertible by reversible transaminations.

Administration, Oral↗
PubMedDate not supplied

Leucine and manifestation of antitumor activity by valine-depleted amino acid imbalance.

With a commercially available balanced 10% amino acid solution as control (I), imbalance solutions were prepared by the removal of valine (II), valine and leucine (III), valine and isoleucine (IV), and valine, leucine, and isoleucine (V). The solutions, in combination with total parenteral nutrition, were given to rats with AH-109A hepatoma for 7 consecutive days to evaluate antitumor activity. Although there were no significant differences in carcass weight after treatment among groups I-IV, a decrease was noted in group V. Tumor weights in groups II-V, relative to that in group I, were 39, 57, 43, and 44%, respectively. Antitumor activity was thus noted in all imbalance groups, although activity in group III was lower than that in group II. These results indicate that the concurrent depletion of leucine and/or isoleucine along with valine is undesirable because of lower antitumor activity and an adverse effect on host development. Leucine is thus suggested to play an important role in augmenting the activity of valine-depleted imbalance.

Amino Acids↗
PubMed1992

Enzymatic characterisation of the multifunctional enzyme delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase from Streptomyces clavuligerus.

delta-(L-alpha-Aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetase, the multienzyme catalyzing the formation of ACV from the constituent amino acids and ATP in the presence of Mg2+ and dithioerythritol, was purified about 2700-fold from Streptomyces clavuligerus. The molecular mass of the native enzyme as determined by gel filtration chromatography is 560 kDa, while that determined by denaturing gel electrophoresis is 500 kDa. The enzyme is able to catalyze pyrophosphate exchange in dependence on L-cysteine and L-valine, but no L-alpha-aminoadipic-acid-dependent ATP/PPi exchange could be detected. Other L-cysteine- and L-valine-activating enzymes present in crude extracts were identified as aminoacyl-tRNA synthetases which could be separated from ACV synthetase. The molecular mass of these enzymes is 140 kDa for L-valine ligase and 50 kDa for L-cysteine ligase. The dissociation constants have been estimated, assuming three independent activation sites, to be 1.25 mM and 1.5 mM for cysteine and ATP, and 2.4 mM and 0.25 mM for valine and ATP, respectively. The enzyme forms a thioester with alpha-aminoadipic acid and with valine in a molar ratio of 0.6:1 (amino acid/enzyme). Thus, the bacterial ACV synthetase is a multifunctional peptide synthetase, differing from fungal ACV synthetases in its mechanism of activation of the non-protein amino acid.

Amino Acyl-tRNA Synthetases↗