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Relações valina:lisina disgestíveis em dietas com nível de proteína bruta reduzido em frangos de corte; Relations valine:lysine digestible in diets with reduced crude protein level in broilers

Caetano, Vinícius Camargo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 11/07/2013 PT
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Este estudo teve como objetivo avaliar relações de valina:lisina digestíveis em dietas com teor reduzido de proteína bruta e os efeitos desta redução sobre desempenho e rendimento de carcaça em frangos de corte. Foram utilizados 1200 pintos machos de um dia de idade, seguindo modelo inteiramente casualizado, com seis tratamentos de seis repetições (exceto controle, com 10 repetições), compostos por 30 aves cada. O tratamento controle (T1) foi formulado seguindo os níveis de proteína bruta (PB) e aminoácidos (AAs) recomendados e os demais tratamentos (T2 a T6) tiveram seus níveis de PB reduzidos (4% em relação ao controle) e variaram em função da relação valina:lisina digestíveis, com 5 níveis equidistantes com intervalos de 0,07:1, variando de 0,63:1 e 0,91:1 em dietas até 21 dias, e 0,64:1 e 0,92:1 em dietas após 21 dias, respectivamente. Foram mensurados as seguintes características de desempenho: ganho de peso, consumo de ração, conversão alimentar, viabilidade criatória e índice de eficiência produtiva. Aos 46 dias de idade seis animais por repetição foram abatidos para determinação de rendimento de carcaça e de cortes comerciais. A cama também foi colhida no começo e final do experimento e seus níveis de nitrogênio analisados para determinação do nitrogênio excretado. As diferentes relações valina:lisina digestíveis não influenciaram o desempenho dos animais (P>0...

Linking Central Metabolism with Increased Pathway Flux: l-Valine Accumulation by Corynebacterium glutamicum

Radmacher, Eva; Vaitsikova, Adela; Burger, Udo; Krumbach, Karin; Sahm, Hermann; Eggeling, Lothar
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /05/2002 EN
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Mutants of Corynebacterium glutamicum were made and enzymatically characterized to clone ilvD and ilvE, which encode dihydroxy acid dehydratase and transaminase B, respectively. These genes of the branched-chain amino acid synthesis were overexpressed together with ilvBN (which encodes acetohydroxy acid synthase) and ilvC (which encodes isomeroreductase) in the wild type, which does not excrete l-valine, to result in an accumulation of this amino acid to a concentration of 42 mM. Since l-valine originates from two pyruvate molecules, this illustrates the comparatively easy accessibility of the central metabolite pyruvate. The same genes, ilvBNCD, overexpressed in an ilvA deletion mutant which is unable to synthesize l-isoleucine increased the concentration of this amino acid to 58 mM. A further dramatic increase was obtained when panBC was deleted, making the resulting mutant auxotrophic for d-pantothenate. When the resulting strain, C. glutamicum 13032ΔilvAΔpanBC with ilvBNCD overexpressed, was grown under limiting conditions it accumulated 91 mM l-valine. This is attributed to a reduced coenzyme A availability and therefore reduced flux of pyruvate via pyruvate dehydrogenase enabling its increased drain-off via the l-valine biosynthesis pathway.

Transaminase B from Escherichia coli: Quaternary Structure, Amino-Terminal Sequence, Substrate Specificity, and Absence of a Separate Valine-α-Ketoglutarate Activity†

Lee-Peng, Fong-Chia; Hermodson, Mark A.; Kohlhaw, Gunter B.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1979 EN
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Transaminase B (branched-chain amino acid aminotransferase, EC 2.6.1.42), the ilvE gene product, was purified to apparent homogeneity from an Escherichia coli K-12 strain which carries the ilvE gene both on the host chromosome and on a plasmid. The oligomeric structure of the enzyme, as determined by analytical ultracentrifugation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was confirmed to be that of a hexamer with a molecular weight of about 182,000 and apparently identical subunits. Cross-linking with dimethylsuberimidate yielded trimers, dimers, and monomers, but essentially no species of higher molecular weight. These results are consistent with a double-trimer arrangement of the subunits in native enzyme. The amino-terminal sequence was found to be: Gly Thr Lys Lys Ala Asp Tyr Ile (Trp) Phe Asn Gly (Thr) (Met) Val. Purified transaminase B catalyzed transamination between α-ketoglutarate and l-isoleucine, l-leucine, l-valine, and, to a lesser extent, l-phenylalanine and l-tyrosine, the latter reacting very sluggishly. The enzyme was free of aspartate transaminase and of transaminase C. The apparent Km values for the branched-chain α-ketoacids were smaller than those for the corresponding amino acids. The lowest Km was recorded for dl-α-keto-β-methyl-n-valerate...

Poliovirus capsid proteins derived from P1 precursors with glutamine-valine cleavage sites have defects in assembly and RNA encapsidation.

Ansardi, D C; Morrow, C D
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1993 EN
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Assembly of poliovirus virions requires proteolytic cleavage of the P1 capsid precursor polyprotein between two separate glutamine-glycine (QG) amino acid pairs by the viral protease 3CD. In this study, we have investigated the effects on P1 polyprotein processing and subsequent assembly of processed capsid proteins caused by substitution of the glycine residue at the individual QG cleavage sites with valine (QG-->QV). P1 cDNAs encoding the valine substitutions were created by site-directed mutagenesis and were recombined into wild-type vaccinia virus to generate recombinant vaccinia viruses which expressed the mutant P1 precursors. The recombinant vaccinia virus-expressed mutant P1 polyproteins were analyzed for proteolytic processing defects in cells coinfected with a recombinant vaccinia virus (VVP3) that expresses the poliovirus 3CD protease and for processing and assembly defects by using a trans complementation system in which P1-expressing recombinant vaccinia viruses provide capsid precursor to a defective poliovirus genome that does not express functional capsid proteins (D. C. Ansardi, D. C. Porter, and C. D. Morrow, J. Virol. 67:3684-3690, 1993). The QV-substituted precursors were proteolytically processed at the altered sites both in cells coinfected with VVP3 and in cells coinfected with defective poliovirus...

Role of the leu-3 Cistron in the Regulation of the Synthesis of Isoleucine and Valine Biosynthetic Enzymes of Neurospora

Olshan, Arthur R.; Gross, S. R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1974 EN
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The production by Neurospora of the enzymes of isoleucine and valine synthesis in response to specific end product-derived signals depends upon the presence of an effective leu-3 regulatory product and its effector α-isopropylmalate (α-IPM). In leu-3+ strains, threonine deaminase production is repressed as a function of available isoleucine, acetohydroxy acid synthetase as a function of valine, and the isomeroreductase and dihydroxy acid dehydratase as a function of isoleucine and leucine. In the absence of an effective leu-3 regulatory product, α-isopropylmalate, or both, the production of isoleucine and valine biosynthetic enzymes is fixed at or near fully repressed levels even under conditions of severe end product limitation. Thus, in addition to its involvement in the regulation of expression of the three structural genes of leucine synthesis, the leu-3 α-IPM regulatory product is necessary for full expression of at least four genes specifying the structure of the enzymes of isoleucine and valine synthesis. It is suggested that the leu-3 α-IPM regulatory element may facilitate transcription of the genetically dispersed cistrons either by imposing specificity on ribonucleic acid polymerase for structurally similar promoters adjacent to each of the cistrons or by “opening” promoters after interaction with nearly identical stretches of deoxyribonucleic acid near each of the structural genes.

Control of Isoleucine, Valine, and Leucine Biosynthesis VI. Effect of 5′,5′,5′-Trifluoroleucine on Repression in Salmonella typhimurium

Freundlich, Martin; Trela, John M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1969 EN
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The leucine analogue 5′,5′,5′,-trifluoroleucine (fluoroleucine) replaced leucine for repression of the isoleucine-valine biosynthetic enzymes in Salmonella typhimurium. In contrast, the analogue had no effect on derepression of the leucine biosynthetic enzymes in leucine auxotrophs grown on limiting amounts of leucine. The effect of fluoroleucine on repression appeared to be specific for leucine since derepression of the isoleucine-valine enzymes due to an isoleucine or valine limitation was not affected by the analogue. The prevention of derepression by fluoroleucine was probably due to repression and not to the formation of false proteins, since the analogue had no effect on the derepression of a number of enzymes unrelated to the isoleucine-valine pathway. Fluoroleucine was able to attach to leucine transfer ribonucleic acid (tRNA) as evidenced by the ability of the analogue to protect about 70% of leucine tRNA from oxidation by periodate. We propose that the differential effects of fluoroleucine on repression are due to differences in the ability of the analogue to bind to the various species of leucine tRNA.

Valine-Specific tRNA-like Structure in Turnip Yellow Mosaic Virus RNA*

Yot, Pierre; Pinck, Monique; Haenni, Anne-Lise; Duranton, Henri M.; Chapeville, François
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1970 EN
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The 3′ terminal nucleotide of turnip yellow mosaic virus (TYMV) RNA (23-25 S) may be esterified with valine in the presence of ATP and an enzyme preparation from Escherichia coli. The nucleotide composition near the valine-binding site is different for TYMV RNA and tRNAVal from cabbage, as shown by comparison of the valine adducts of nucleotides labeled with radioactive valine in T1 RNase digests. Consequently, host tRNAVal is not involved in the observed charging of TYMV RNA with valine. The TYMV RNA appears to have a tRNA-like structure, at or near its 3′ end, that is recognized by three different enzymes which specifically catalyze reactions involving tRNA.

Multiplicity of Isoleucine, Leucine, and Valine Transport Systems in Escherichia coli K-12

Guardiola, John; De Felice, Maurilio; Klopotowski, Tadeusz; Iaccarino, Maurizio
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1974 EN
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The kinetics of isoleucine, leucine, and valine transport in Escherichia coli K-12 has been analyzed as a function of substrate concentration. Such analysis permits an operational definition of several transport systems having different affinities for their substrates. The identification of these transport systems was made possible by experiments on specific mutants whose isolation and characterization is described elsewhere. The transport process with highest affinity was called the “very-high-affinity”process. Isoleucine, leucine, and valine are substrates of this transport process and their apparent Km values are either 10−8, 2 × 10−8, or 10−7 M, respectively. Methionine, threonine, and alanine inhibit this transport process, probably because they are also substrates. The very-high-affinity transport process is absent when bacteria are grown in the presence of methionine, and this is due to a specific repression. Methionine and alanine were also found to affect the pool size of isoleucine and valine. Another transport process is the “high-affinity” process. Isoleucine, leucine, and valine are substrates of this transport process, and their apparent Km value is 2 × 10−6 M for all three. Methionine and alanine cause very little or no inhibition...

UPTAKE OF VALINE AND GLYCYLVALINE BY LEUCONOSTOC MESENTEROIDES1

Shelton, Damon C.; Nutter, William E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1964 EN
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Shelton, Damon C. (West Virginia University Medical Center, Morgantown), and William E. Nutter. Uptake of valine and glycylvaline by Leuconostoc mesenteroides. J. Bacteriol. 88:1175–1184. 1964.—Uptake systems for valine and glycylvaline were studied in growing cultures and non-growing cellular suspensions of Leuconostoc mesenteroides. Glycylvaline promoted growth more rapidly than did valine. Other dipeptides were shown to be antagonistic to the utilization of glycylvaline by the organism. The experiments with cellular suspensions were done with the use of combinations of labeled and unlabeled amino acids and peptides. Results showed that different uptake systems were present in L. mesenteroides for the uptake of valine and glycylvaline. Both systems were energy-dependent and readily saturated. The synthesis, purification, and chromatographic identification of glycyl-dl-valine-1-C14 is described.

Multivalent Repression of Isoleucine-Valine Biosynthesis in Saccharomyces cerevisiae

Magee, P. T.; Hereford, Lynna M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1969 EN
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Regulation of the biosynthesis of four of the five enzymes of the isoleucine-valine pathway was studied in Saccharomyces cerevisiae. A method is described for limiting the growth of a leucine auxotroph by using valine as a competitor for the permease. Limitation for isoleucine and valine was accomplished by the use of peptides containing these amino acids conjugated with glycine as nutritional supplements for auxotrophs. The enzymes were repressed on synthetic medium containing isoleucine, valine, and leucine, as well as on broth supplemented with these amino acids. Limitation for any of the three branched-chain amino acids led to derepression of the isoleucine-valine biosynthetic pathway. Maximal derepression ranged from 3-fold for threonine deaminase to approximately 10-fold for acetohydroxyacid synthase. (Two of the enzymes, acetohydroxyacid synthase and dihydroxyacid dehydrase, may be controlled by a mechanism different from that regulating threonine deaminase.) Possible molecular mechanisms for multivalent repression are discussed.

Nucleotide sequence of a spinach chloroplast valine tRNA.

Sprouse, H M; Kashdan, M; Otis, L; Dudock, B
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 11/06/1981 EN
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The nucleotide sequence of a spinach chloroplast valine tRNA (sp. chl. tRNA Val) has been determined. This tRNA shows essentially equal homology to prokaryotic valine tRNAs (58-65% homology) and to the mitochondrial valine tRNAs of lower eukaryotes (yeast and N. crassa, 61-62% homology). Sp. chl. tRNA Val shows distinctly lower homology to mouse mitochondrial valine tRNA (53% homology) and to eukaryotic cytoplasmic valine tRNAs (47-53% homology). Sp. chl. tRNA Val, like all other chloroplast tRNAs sequenced, contains a methylated GG sequence in the dihydrouridine loop and lacks unusual structural features which have been found in several mitochondrial tRNAs.

Conformation of high-molecular-weight poly(L-valine) in solid state.

Yamashita, S; Yamashita, T
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1975 EN
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Poly(L-valine) in various degrees of polymerization was prepared from the N-carboxyanhydride of L-valine. The high-molecular-weight polymer was fibrous and capable of forming an oriented film when cast from trifluoroacetic acid solution. The comformations were examined by Raman spectroscopy. The Raman and infrared spectra of high-molecular-weight polymer were quite different from those of low-molecular-weight and tri-fluoroacetic-acid-treated high-molecular-weight polymers. The spectral data in the amide A, I, II, III, and V regions indicated that high-molecular-weight poly(L-valine) is possibly in the alpha-helical conformation, while low-molecular-weight poly(L-valine) and high--molecular-weight poly(L-valine) treated with trifluoroacetic acid are in the beta-conformation.

The biosynthesis of valine from isobutyrate by Peptostreptococcus elsdenii and Bacteroides ruminicola

Allison, Milton J.; Peel, J. L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1971 EN
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1. Growing cultures of Peptostreptococcus elsdenii and Bacteroides ruminicola incorporate 14C from [1-14C]isobutyrate into the valine of cell protein. With P. elsdenii some of the 14C is also incorporated into leucine. 2. Crude cell-free extracts of both organisms in the presence of glutamine, carbon dioxide and suitable sources of energy and electrons incorporate 14C from [1-14C]isobutyrate into valine but not into leucine. 3. With extracts of P. elsdenii treated with DEAE-cellulose the reaction is dependent on ATP, CoA, thiamin pyrophosphate, molecular hydrogen and a low-potential electron carrier (ferredoxin, flavodoxin or benzyl viologen). 4. The same extracts incorporate 14C from NaH14CO3 into valine in the presence of isobutyrate plus ATP, CoA, glutamine and ferredoxin; isobutyryl-CoA or isobutyryl phosphate plus CoA will replace the isobutyrate plus CoA and ATP. With acetyl phosphate in place of isobutyryl phosphate, 14C is incorporated into alanine. With isovalerate or 2-methylbutyrate in place of isobutyrate, 14C is incorporated into leucine and isoleucine respectively. 5. When carrier 2-oxoisovalerate is added to the carboxylating system 14C from [1-14C]isobutyrate passes into the oxo acid fraction. 6. It is concluded that these two organisms form valine from isobutyrate by the sequence isobutyrate→isobutyryl-CoA→2-oxoisovalerate→valine and that the reductive carboxylation of isobutyrate is catalysed by a system similar to the pyruvate synthetase of clostridia and photosynthetic bacteria.

Transport of leucine, isoleucine and valine by luminal membrane vesicles from rabbit proximal tubule.

Jørgensen, K E; Kragh-Hansen, U; Sheikh, M I
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1990 EN
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1. Transport of L- and D-isomers of leucine, isoleucine and valine by luminal membrane vesicles prepared from either the convoluted part (pars convoluta) or the straight part (pars recta) of rabbit proximal tubule was studied by a rapid filtration technique and by a spectrophotometric method using a potential-sensitive carbocyanine dye. 2. Both types of renal membrane vesicle take up the amino acids in a Na(+)-dependent, H(+)-independent and electrogenic manner. The L-isomers are transported with higher affinities than their corresponding D-forms, of which only D-leucine is taken up to a significant extent. 3. Membrane vesicles prepared from pars convoluta take up the L-amino acids by a single and common system. Filtration studies showed that the Km values for L-leucine and L-valine transport are, on average, 0.23 and 0.83 mM, respectively. The values of KA (the concentration of amino acid producing a half-maximal optical response) are comparable to those of Km, namely 0.18 mM for L-leucine and 0.60 mM for L-valine. KA for L-isoleucine transport was found to be 0.19 mM. D-Leucine is taken up by the same system but with a much lower affinity (KA = 7.2 mM). 4. Membrane vesicles prepared from pars recta possess two, and probably common...

Interference between leucine, isoleucine and valine during intestinal absorption

Szmelcman, S.; Guggenheim, K.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1966 EN
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1. The reciprocal interference between l-leucine, l-isoleucine and l-valine during absorption was studied in rats both in vivo and with an everted-sac preparation in vitro. 2. After feeding with the amino acids alone there was a considerable increase in their concentration in the intestinal lumen followed by a rapid disappearance, indicating efficient absorption. Absorption was reflected by a high concentration of the respective amino acids in the portal plasma. Isoleucine and valine inhibited the absorption of leucine, and leucine inhibited the absorption of isoleucine and valine. Inhibition of absorption by the interfering amino acid was generally partly overcome after 30–60min., probably through the absorption of the interfering amino acid. At that time the rise in the concentration of the amino acid in portal plasma began. 3. These results were confirmed by experiments in vitro: isoleucine and valine inhibited the absorption rate of leucine, and leucine that of isoleucine and valine. 4. Active absorption of amino acids was rapid at low concentrations and depressed at higher concentrations.

l-Valine Production with Pyruvate Dehydrogenase Complex-Deficient Corynebacterium glutamicum▿

Blombach, Bastian; Schreiner, Mark E.; Holátko, Jiří; Bartek, Tobias; Oldiges, Marco; Eikmanns, Bernhard J.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
EN
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Corynebacterium glutamicum was engineered for the production of l-valine from glucose by deletion of the aceE gene encoding the E1p enzyme of the pyruvate dehydrogenase complex and additional overexpression of the ilvBNCE genes encoding the l-valine biosynthetic enzymes acetohydroxyacid synthase, isomeroreductase, and transaminase B. In the absence of cellular growth, C. glutamicum ΔaceE showed a relatively high intracellular concentration of pyruvate (25.9 mM) and produced significant amounts of pyruvate, l-alanine, and l-valine from glucose as the sole carbon source. Lactate or acetate was not formed. Plasmid-bound overexpression of ilvBNCE in C. glutamicum ΔaceE resulted in an approximately 10-fold-lower intracellular pyruvate concentration (2.3 mM) and a shift of the extracellular product pattern from pyruvate and l-alanine towards l-valine. In fed-batch fermentations at high cell densities and an excess of glucose, C. glutamicum ΔaceE(pJC4ilvBNCE) produced up to 210 mM l-valine with a volumetric productivity of 10.0 mM h−1 (1.17 g l−1 h−1) and a maximum yield of about 0.6 mol per mol (0.4 g per g) of glucose.

COMPARISON OF THE RELATIVE SYNTHESIS OF THE PROTEINS OF THE 50S RIBOSOMAL SUBUNIT IN GROWING AND VALINE-DEPRIVED HELA CELLS

Pawlowski, Philip J.; Vaughan, Maurice H.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/02/1972 EN
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Quantitative studies of the synthesis of the ribosomal proteins of the 50S ribosomal subunit have been made with growing versus valine-deprived HeLa cells. The synthesis of total cell protein and 50S subunits was also compared between the growing and nongrowing cells. It was found that between 12 and 20 hr of valine deprivation the net synthesis of 50S subunits drops to approximately 8% of that in control cells while the over-all synthesis of 50S subunit ribosomal proteins declines to approximately 12% of that in the controls. However, the synthesis rates for each of two particular 50S subunit proteins decline to approximately 8% of the rates in the growing cells, indicating that the synthesis of one of these proteins may be rate limiting for 50S subunit biosynthesis in valine-deprived HeLa cells. Other evidence indicates that the regulation of synthesis of the ribosomal proteins in valine deprivation depends on control at the level of transcription or translation rather than being a function of the relative valine content of these proteins.

The Amino Acid Valine Is Secreted in Continuous-Flow Bacterial Biofilms▿ ‡

Valle, Jaione; Da Re, Sandra; Schmid, Solveig; Skurnik, David; D'Ari, Richard; Ghigo, Jean-Marc
Fonte: American Society for Microbiology (ASM) Publicador: American Society for Microbiology (ASM)
Tipo: Artigo de Revista Científica
EN
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Biofilms are structured communities characterized by distinctive gene expression patterns and profound physiological changes compared to those of planktonic cultures. Here, we show that many gram-negative bacterial biofilms secrete high levels of a small-molecular-weight compound, which inhibits the growth of only Escherichia coli K-12 and a rare few other natural isolates. We demonstrate both genetically and biochemically that this molecule is the amino acid valine, and we provide evidence that valine production within biofilms results from metabolic changes occurring within high-density biofilm communities when carbon sources are not limiting. This finding identifies a natural environment in which bacteria can encounter high amounts of valine, and we propose that in-biofilm valine secretion may be the long-sought reason for widespread but unexplained valine resistance found in most enterobacteria. Our results experimentally validate the postulated production of metabolites that is characteristic of the conditions associated with some biofilm environments. The identification of such molecules may lead to new approaches for biofilm monitoring and control.

Reversal of Chlorsulfuron-Induced Inhibition of Mitotic Entry by Isoleucine and Valine 1

Rost, Thomas L.; Reynolds, Thomas
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1985 EN
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Pea (Pisum sativum L. cv Alaska) root tips were excised and cultured aseptically in White's medium. Cultures were treated immediately or after a 24 hour equilibration time with 28 nanomolar chlorsulfuron plus isoleucine and valine (each 0.1 millimolar), isoleucine and valine, or untreated. The percentage of mitotic figures in untreated control roots sampled immediately after excision showed a transitory drop and recovery within 24 hours (an excision effect). In chlorsulfuron-treated roots, the percentage of mitotic figures did not recover. In roots treated with chlorsulfuron plus isoleucine and valine, a complete recovery did occur. If roots were treated with chlorsulfuron 24 hours after excision, the percentage of mitotic figures was reduced to near 0 by 8 hours. In roots treated with chlorsulfuron plus isoleucine and valine, no reduction in mitotic figures occurred. The complete reversal of chlorsulfuron-inhibited mitotic entry by isoleucine and valine implicates these amino acids, in some manner, with the control of cell cycles progression.

Purification and catalytic properties of L-valine dehydrogenase from Streptomyces cinnamonensis.

Priestley, N D; Robinson, J A
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/08/1989 EN
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NAD+-dependent L-valine dehydrogenase was purified 180-fold from Streptomyces cinnamonensis, and to homogeneity, as judged by gel electrophoresis. The enzyme has an Mr of 88,000, and appears to be composed of subunits of Mr 41,200. The enzyme catalyses the oxidative deamination of L-valine, L-leucine, L-2-aminobutyric acid, L-norvaline and L-isoleucine, as well as the reductive amination of their 2-oxo analogues. The enzyme requires NAD+ as the only cofactor, which cannot be replaced by NADP+. The enzyme activity is significantly decreased by thiol-reactive reagents, although purine and pyrimidine bases, and nucleotides, do not affect activity. Initial-velocity and product-inhibition studies show that the reductive amination proceeds through a sequential ordered ternary-binary mechanism; NADH binds to the enzyme first, followed by 2-oxoisovalerate and NH3, and valine is released first, followed by NAD+. The Michaelis constants are as follows; L-valine, 1.3 mM; NAD+, 0.18 mM; NADH, 74 microM; 2-oxoisovalerate, 0.81 mM; and NH3, 55 mM. The pro-S hydrogen at C-4' of NADH is transferred to the substrate; the enzyme is B-stereospecific. It is proposed that the enzyme catalyses the first step of valine catabolism in this organism.