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At least 19 recordsLinked to original sources
PubMed1996

Maintenance requirement for valine and efficiency of its use above maintenance for accretion of whole body valine and protein in young chicks.

Experiments were conducted with chicks during the period 10-20 d posthatching to assess valine accretion and protein accretion as a function of incremental valine intakes between 5 and 95% of its ideal level (requirement for maximal growth). Chemically defined crystalline amino acid diets were fed, and amino acids other than valine were maintained at minimized excess levels as valine was increased. With dietary valine concentrations representing 5, 10, 40, 55, 70 and 95% of the ideal level, weight gain (r2 = 0.98), protein accretion (r2 = 0.98) and valine accretion (r2 = 0.99) increased linearly (P < 0.01) as a function of valine intake. Slope of the valine accretion curve was 0.73 +/- 0.02, and there was no indication of decreased valine utilization as valine intake increased to 95% of its required level for maximal growth. Using the linear regression equation, i.e., valine accretion (Y) regressed on valine intake (X), the maintenance valine requirement (X at Y zero) was 18.4 mg/d or 48.8 mg/d per kg body weight3/4. Whole body valine was 4.72 g/100 g whole body protein accreted and was constant at all levels of valine intake. At zero protein accretion, however, valine accretion was negative (-3.8 mg/d). Thus, the valine requirement for zero valine accretion (48.8 mg/d per kg(3/4) was higher than the valine requirement for zero protein accretion (32.4 mg/d per kg3/4). In a subsequent experiment, also involving whole body valine and protein accretion, valine doses of 40, 55 and 70% of ideal were compared using amino acid-balanced diets (amino acids other than valine at 55, 70 and 85% of ideal levels, respectively) or imbalanced diets (amino acids other than valine at a constant 100% of their ideal levels). Straight-line (P < 0.01) valine and protein accretion responses occurred, but slope of the response curves (accretion vs. valine intake) was lower in the imbalanced series than in the balanced series. The results of these studies suggest a constant utilization above maintenance of absorbed valine over a wide range of valine intake.

Analysis of Variance↗
PubMed1997

L-delta-(alpha-Aminoadipoyl)-L-cysteinyl-D-valine synthetase: thioesterification of valine is not obligatory for peptide bond formation.

L-delta-(alpha-Aminoadipoyl)-L-cysteinyl-D-valine (ACV) synthetase is probably the simplest known peptide synthetase in terms of the number of reactions catalyzed. In the "thiol-template" proposal for nonribosomal peptide synthesis, a key step is transfer of aminoacyl groups derived from the substrates to enzyme-bound thiols prior to peptide bond formation. No incorporation of 18O was seen in AMP isolated from the reaction mixture when di[18O]valine was incubated with relatively large amounts of active synthetase and MgATP. We therefore utilized di[18O]valine as a substrate for the biosynthesis of the diastereomeric dipeptides L-O-(methylserinyl)-L-valine and L-O-(methylserinyl)-D-valine [Shiau, C.-Y., Baldwin, J. E., Byford, M. F., Sobey, W. J., & Schofield, C. J. (1995) FEBS Lett. 358, 97-100]. In the L-O-(methylserinyl)-L-valine product, no significant loss of 18O was observed. However, in the L-O-(methylserinyl)-D-valine product, a significant loss of one or both 18O labels was observed. Thus, both peptide bond formation and the epimerization of the valine residue can both occur before formation of any thioester bond to the valine carboxylate in the biosynthesis of these dipeptides. The usual qualitative test for thioesterification of substrates to the synthetase, lability of enzyme-bound radiolabeled amino acid to performic acid, proved inconclusive in our hands. These results require a new mechanism for the enzymic synthesis of L-O-(methylserinyl)-L-valine and L-O-(methylserinyl)-D-valine and imply that a revised mechanism for ACV synthesis is also required.

2-Aminoadipic Acid↗
PubMed1986

Valine kinetics at graded valine intakes in young men.

Twelve young men, six subjects in each group studied in two phases, participated in an experiment to explore the relationships between valine intake, plasma valine concentrations, and valine kinetics, using 1-[13C]valine as a tracer. Below a valine intake of about 20 mg.kg-1.day-1 plasma valine concentrations reached a low and relatively constant level. The rate of valine oxidation fell with the decline in the intake of amino acid. Below valine intakes of 16 mg.kg-1.day-1, the mean daily rate of oxidation was estimated to be generally higher than the intake level, implying a negative valine balance during the 24 h day. These findings indicate that an intake of 10 mg valine kg-1.day-1 would not be adequate to maintain protein nutritional status. Our results are discussed in relation to the currently accepted 1973 FAO/WHO value of 10 mg.kg-1.day-1 as being the upper range of the valine requirement in healthy adult humans.

Adolescent↗
PubMed1962

Isoleucine and valine metabolism in Escherichia coli. XI. Valine inhibition of the growth of Escherichia coli strain K-12.

Leavitt, Richard I. (Harvard Medical School, Boston, Mass.) and H. E. Umbarger. Isoleucine and valine metabolism in Escherichia coli. XI. Valine inhibition of the growth of Escherichia coli strain K-12. J. Bacteriol. 83:624-630. 1962.-The inhibition of the growth of Escherichia coli strain K-12 by valine was shown to be due to the sensitivity of the acetohydroxybutyrate-forming system to valine. It was demonstrated that both E. coli strain W, a strain whose growth is unaffected by valine, and a valine-resistant mutant of strain K-12 have acetolactate- and acetohydroxybutyrate-forming systems which are less sensitive to valine than that of strain K-12. It was further shown that alpha-aminobutyrate accumulates in the culture fluid of the valine-sensitive strain when incubated in the presence of valine. The levels of valine in the "free amino acid pool" were examined and found to be related to the differences in valine sensitivity of the acetolactate-forming systems of the three strains.

Amino Acids↗
PubMed1992

Valine oxidation: the synthesis and evaluation of L-[3-3H]valine as a tracer in vivo.

The suitability of L-[3-3H]valine for measuring valine oxidation was studied by comparing its oxidation rate with that of L-[1-14C]valine in rats and pigs. L-[3-3H]valine was synthesized by removal of the tritium on carbon-2 of L-[2,3-3H]valine by acetylation. The acetyl group was removed enzymatically using pig renal acylase 1 (EC 3.5.1.14) and the product was purified by ion-exchange and paper chromatography. For the first rat experiment L-[3-3H]valine was synthesized in our laboratory; for the subsequent experiments it was produced by Amersham International plc. In the first experiment in rats the two tracers were given by injection and 14CO2 was collected for 2 h. The oxidation of tritiated valine was significantly higher than that of L-[1-14C]valine. In a second experiment there was no difference. This was probably due to the higher purity of the labelled valine which, for the second experiment, was shown by nuclear magnetic resonance to contain only one tritium atom. In a study with pigs in which the two tracers were given by continuous infusion there was no significant difference between them in flux or oxidation. The results of this experiment were used to evaluate a model to estimate amino acid requirements. With pigs given a methionine-limiting diet a reduction in methionine intake, by reducing protein accretion, increased valine oxidation by the same proportion.

Amino Acids↗
PubMed1964

VALINE-ISOLEUCINE METABOLISM IN ACETOBACTER SUBOXYDANS AND THE INHIBITION OF GROWTH BY VALINE.

Kerwar, Suresh S. (Oregon State University, Corvallis), Vernon, H. Cheldelin, and L. W. Parks. Valine-isoleucine metabolism in Acetobacter suboxydans and the inhibition of growth by valine. J. Bacteriol. 88:179-186. 1964.-Extracts of Acetobacter suboxydans can synthesize valine and isoleucine via acetolactate and acetohydroxybutyrate, respectively. The amounts of these amino acids synthesized from different intermediates were determined. The pathways appear to be identical to those described for yeast, Neurospora, and Escherichia coli. When exogenous valine was added to a synthetic growth medium inoculated with A. suboxydans, no growth of the culture was observed. The inhibitory effect of valine was reversed by the addition of isoleucine. The site and mechanism of valine inhibition were investigated. Threonine deaminase was inhibited by valine and isoleucine but not by leucine. Repression of the deaminase by isoleucine but not by valine was indicated. The data reported in this paper suggest that valine prevented growth of the organism through false feedback inhibition of threonine deaminase, thereby limiting isoleucine biosynthesis.

Acetobacter↗
PubMed1993

A mechanism for valine-resistant growth of Escherichia coli K-12 supported by the valine-sensitive acetohydroxy acid synthase IV activity from ilvJ662.

Acetohydroxy acid synthase (EC 4.1.3.18; AHAS) isozymes I and III are expressed in Escherichia coli strain K-12 and, when inhibited by L-valine, cannot support cell growth. AHAS IV, expressed from mutation at ilvJ662, exhibits valine-sensitivity similar to that of AHAS III, yet AHAS IV does support cell growth in valine minimal medium. Rate equations were derived for AHAS III and AHAS IV reaction in crude extracts and for partially purified AHAS IV. Values of kinetic constants in these equations were determined in order to model a probable reaction mechanism. Computer modeling of initial velocity reactions at physiological substrate concentrations simulated consequences of valine-inhibition and revealed that AHAS IV synthesized AHB at a maximal rate over four times faster than AHAS III under these conditions. The simulations predicted that cells depending upon AHAS III for growth in valine minimal medium would accumulate higher levels of 2-ketobutyrate than cells using AHAS IV. Experiments on growth inhibition by valine revealed more than a five-fold difference in 2-ketobutyrate accumulation, thus confirming these predictions. These data support the hypothesis that valine inhibition of growth is a consequence of 2-ketobutyrate accumulation to toxic levels. We propose that the valine-inhibited AHAS IV activity prevents growth inhibition by keeping 2-ketobutyrate accumulation to a lower level than resulting from AHAS III activity.

Acetolactate Synthase↗
PubMed1988

The transfer coefficients for L-valine and the rate of incorporation of L-[1-14C] valine into proteins in normal adult rat brain.

An autoradiographic method for the measurement of the rate of valine incorporation into brain proteins is described. The transfer coefficients for valine into and out of the brain and the rate of valine incorporation into normal rat brain proteins are given. The valine incorporation and the transfer constants of valine between different biological compartments are provided for 14 gray matter and 2 white matter structures of an adult rat brain. The rate of valine incorporation varies between 0.52 +/- 0.19 nmol/g/min in white matter and 1.94 +/- 0.47 in inferior colliculus (gray matter). Generally, the rate of valine incorporation is about three to four times higher in the gray matter than in the white matter structures.

Animals↗
PubMed1968

Formation of a complex between valine and intestinal mucosal lipid; its possible role in valine absorption.

During intestinal absorption amino acids must traverse the lipid-rich epithelial cell membrane, possibly in a lipid-soluble form. In a search for such a form, we have determined the ability of lipid extracted from intestinal mucosa to bind valine. After incubation in a valine-containing medium this lipid (defined as the heptane-soluble fraction) contained, on the average, 3.63 micromoles of valine per 100 mg of lipid. Cyanide (0.002 m), 2,4-dinitrophenol (0.0002 m), and anaerobic conditions had little effect on this process. Valine uptake into the lipid fraction of mucosa was complete after 2.5 min. Of a number of sugars and amino acids tested, isoleucine, methionine, and leucine were the most potent inhibitors of valine uptake into lipid. The inhibition by leucine appeared to be competitive. A similar uptake of glucose into the mucosal lipid was not inhibited by leucine, methionine, or isoleucine but was inhibited by galactose. Various phosphoglycerides (but not sphingomyelin) from other sources, used in place of mucosal lipid, were able to carry 20-150 times as much valine into heptane-soluble fraction as were other lipid classes. Some characteristics of the complex are similar to those of the valine transport system.

Animals↗
PubMed1991

Effect of loading doses of L-valine on relative contributions of valine derived from protein degradation and plasma to the precursor pool for protein synthesis in rat brain.

"Flooding" amino acid pools with high doses of labeled amino acids of low specific activity has been proposed to minimize the effects of recycling of amino acids derived from protein degradation on the specific activity of the amino acid precursor pool for protein synthesis. We have examined the influence of recycling on the precursor pool for protein synthesis under conditions in which plasma valine concentrations were normal (0.19 mM) and "flooded" (10-28 mM) by comparing the steady-state specific activity of the tRNA-bound valine with that of the plasma valine. Under normal and "flooding" conditions, the relative contributions of valine from protein degradation to the precursor pool were 63 and 26%, respectively; "flooding" with a plasma level of 28 mM raised the brain acid-soluble pool level to 3.1 mM but was no more effective in decreasing the relative contribution of valine from protein degradation to the precursor pool than "flooding" with a plasma level of 17 mM valine, which raised the brain acid-soluble level only to 2.3 mM. The results of these studies show that "flooding" amino acid pools does indeed reduce the effect of recycling on the precursor amino acid pool for protein synthesis, but it does not totally eliminate it.

Animals↗
PubMed1985

Metabolic conversion of alpha-keto valine to valine in patients with chronic renal failure.

Change in the metabolic conversion rate of alpha-keto valine to valine following oral administration of the analog of the essential amino acid (0.1 g/kgB.W.) is studied in six patients with chronic renal failure and five control subjects under low protein, low and normal energy intake diets. Diet I is composed of 105 kj (25 kcal)/kgB.W. energy and 0.6 g/kgB.W. protein, whereas Diet II is composed of 165 kj (40 kcal)/kgB.W. with the same amount of protein intake. As a result, an increase in plasma keto valine concentration is observed immediately after oral administration, followed by an increase in plasma valine concentration, implying that metabolic conversion of alpha-keto valine to valine occurs within a small amount of time. In addition, the conversion rate appears to be accelerated under Diet II. It is therefore suggested that reutilization of urea nitrogen with the ketoanalog under the low protein diet seems to be promoted under adequate energy intake.

Administration, Oral↗
PubMed1995

Delta-L-(alpha-aminoadipoyl)-L-cysteinyl-D-valine synthetase: isolation of L-cysteinyl-D-valine, a 'shunt' product, and implications for the order of peptide bond formation.

L-Cysteinyl-D-valine was isolated from incubations of L-glutamate, L-cysteine and L-valine with delta-L-(alpha-aminoadipoyl)-L-cysteinyl-D-valine synthetase and identified by 1H NMR and electrospray ionization MS. This is entirely consistent with our prior proposal (Shiau, C.-Y., Baldwin, J.E., Byford, M.F., Sobey, W.J. and Schofield, C.J. (1995) FEBS Lett. 358, 97-100) that the alpha-peptide bond between cysteine and valine is formed before the delta-peptide bond between alpha-aminoadipate and cysteine. The inclusion of L-glutamate, an analogue of L-alpha-aminoadipate, did not result in a detectable amount of tripeptide product, but did increase apparent yields of L-cysteinyl-D-valine. Conceivably, formation of the L-glutamyladenylate stimulates synthesis of the cysteinyl-valine dipeptide indirectly via a conformational change in the enzyme.

Acremonium↗
PubMed1985

Control of isoleucine-valine biosynthesis in a valine-resistant mutant of Escherichia coli K-12 that simultaneously acquired azaleucine-resistance.

A mutant of Escherichia coli K-12 isolated as being growth resistant to L-valine (Valr) was shown also to exhibit growth resistance to 4-azaleucine (Azlr). Transductional analysis indicated that Azlr is cotransduced with Valr at a frequency of 100% and both are linked to leu, ara, and carA. This mutation conferring valine and azaleucine growth resistance resulted in increased levels of isoleucine and valine biosynthetic enzymes as well as those of valyl- and isoleucyl-tRNA synthetases during growth in minimal and enriched media. Acquisition of Vals/Azls results in the restoration of normal regulation of both classes of ilv enzymes and normal patterns of the tRNA Ile species. The overall regulatory patterns observed for individual isoleucine and valine gene products suggest differential participation of isoleucine and valine and/or isoleucyl- and valyl-tRNA's in control of expression of the respective structural genes.

Acetolactate Synthase↗
PubMed1992

Influence of the tumor mass on the valine rate constants and on valine incorporation into proteins in an experimental brain tumor model.

Quantitative autoradiography was used to estimate regional transfer coefficients for valine incorporation and the rate of valine (exogenous and total) incorporation into proteins in an implanted brain-tumor model (AA ascites tumor). Special attention was paid to the evaluation of the tumor mass influence on the transfer coefficients and the rate of incorporation. The size of the tumors used in this study ranged from 2 to 5 mm in diameter. Nine groups of two to three animals each were used to determine the transfer coefficient. The transfer coefficients for movement of the label between different compartments were significantly greater in the tumor than in the normal brain. There is no tumor mass effect on the transfer coefficients or the rate of valine incorporation into proteins in surrounding or remote brain structures. The ratio between specific radioactivities of the free value in tissue and plasma was also measured. Results indicate that approximately the same fraction of the total valine is recycled in cortex as in the tumor tissue. The mean rates of exogenous valine incorporation into proteins (nmol g-1 min-1) is about one order of magnitude greater in the tumor than in the contralateral parietal cortex.

Animals↗
PubMed1996

The rate of valine incorporation into proteins with correction for valine recycling, measured in two brain tumor models and the cortex.

The tissue dilution factor (lambda) for the incorporation of valine into proteins in the rat cortex and in two different tumors, AA ascites and C6 glioma, was determined from measurements of specific activities in the tissue acid-soluble and aminoacyl-tRNA pools and in the plasma. A constant plasma specific activity was achieved by a constant infusion rate of [3H] valine. The data showed that the lambda for valine was the same in the cortex as in the tumors, and the recycling was approximately 36%. There was no difference in the lambda calculated on the basis of the specific activities in the tissue acid-soluble or aminoacyl-tRNA pools. The average dilution factor was found to be 0.64+/-0.05. The rate of valine incorporation into proteins was on average 3.2+/-0.4 and 4.9+/-0.4 nmol/g/min in the cortex for the groups of rats used in the AA ascites and C6 glioma experiments, respectively. In the AA ascites tumor the rate was approximately 41 and 29 nmol/g/min 4 and 7 days after tumor implantation, respectively, whereas in the C6 glioma the rate was approximately 41 and 72 nmol/g/min 6 and 13 days after inoculation, respectively. The tumors had, in comparison with the cortex, a significantly greater volume of distribution of valine. The amounts of valyl-tRNA were significantly greater in the tumors as compared with the normal cortex, with the exception of the glioma 6 days after implantation where the concentration was the same as in the cortex.

Animals↗
PubMed1976

Incorporation of double-labelled valine into delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine by Penicillium chrysogenum.

The incorporation of valine into the LLD-tripeptide, delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine, a precursor of penicillin, was studied by incubating mycelial mats of Penicillium chrysogenum Wis. 49-2105 with double labelled valines. L-valine was incorporated into the LLD-tripeptide without formation of an alpha, beta-didehydrovaline intermediate. Intact D-valine was not incorporated into the LLD-tripeptide.

Carbon Radioisotopes↗