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At least 217 records · Page 12Linked to original sources
PubMed2000

Isolated 2-methylbutyrylglycinuria caused by short/branched-chain acyl-CoA dehydrogenase deficiency: identification of a new enzyme defect, resolution of its molecular basis, and evidence for distinct acyl-CoA dehydrogenases in isoleucine and valine metabolism.

Acyl-CoA dehydrogenase (ACAD) defects in isoleucine and valine catabolism have been proposed in clinically diverse patients with an abnormal pattern of metabolites in their urine, but they have not been proved enzymatically or genetically, and it is unknown whether one or two ACADs are involved. We investigated a patient with isolated 2-methylbutyrylglycinuria, suggestive of a defect in isoleucine catabolism. Enzyme assay of the patient's fibroblasts, using 2-methylbutyryl-CoA as substrate, confirmed the defect. Sequence analysis of candidate ACADs revealed heterozygosity for the common short-chain ACAD A625 variant allele and no mutations in ACAD-8 but a 100-bp deletion in short/branched-chain ACAD (SBCAD) cDNA from the patient. Our identification of the SBCAD gene structure (11 exons; >20 kb) enabled analysis of genomic DNA. This showed that the deletion was caused by skipping of exon 10, because of homozygosity for a 1228G-->A mutation in the patient. This mutation was not present in 118 control chromosomes. In vitro transcription/translation experiments and overexpression in COS cells confirmed the disease-causing nature of the mutant SBCAD protein and showed that ACAD-8 is an isobutyryl-CoA dehydrogenase and that both wild-type proteins are imported into mitochondria and form tetramers. In conclusion, we report the first mutation in the SBCAD gene, show that it results in an isolated defect in isoleucine catabolism, and indicate that ACAD-8 is a mitochondrial enzyme that functions in valine catabolism.

Alternative Splicing↗
PubMed1980

The need of essential amino acids in children. An evaluation based on the intake of phenylalanine, tyrosine, leucine, isoleucine, and valine in children with phenylketonuria, tyrosine amino transferase defect, and maple syrup urine disease.

The diet of children with blocks in the metabolism of five amino acids has been investigated to evaluate the need for these amino acids in the maintenance of normal growth and development. Two children with phenylketonuria, one child with tyrosine aminotransferase defect and one child with maple syrup urine disease are included in the study. The growth and development of the children have been within the normal range except for language development, which was retarded in the maple syrup urine disease child. The need for phenylalanine, phenylalanine and tyrosine combined and isoleucine, leucine, and valine for protein synthesis in growing children was investigated by registering the intake of phenylalanine in the phenylketonuria children, the intake of phenylalanine and tyrosine in the tyrosine amino transferase defect child and isoleucine, leucine and valine in the maple syrup urine disease child. The significance of this intake, defined as the sufficient intake, is discussed, as well as the difference between the sufficient intake and requirement. The sufficient intake is compared with former studies on requirement. There is good agreement between the sufficient intake and requirement of phenylalanine and tyrosine. The sufficient intake of isoleucine, leucine, and valine as judged from our study is lower than in former studies on requirement.

Amino Acids, Essential↗
PubMed1977

Quantitative requirement of the hatchling green sea turtle, Chelonia mydas, for valine, leucine, isoleucine and phenylalanine.

Hatchling green sea turtles were fed purified diets containing 36% crude protein (N X 6.25) to determine the quantitative requirements for valine, leucine, isoleucine and phenylalanine. Expressed as percentage of total dry diet, the hatchling green sea turtle requires 1.3% valine, 1.6% leucine, 1.0% isoleucine and 1.0% phenylalanine (in the presence of 0.5% tyrosine). Within the range of isoleucine-leucine levels investigated, there was no apparent interrelationship between the quantitative requirements of these two amino acids. Growth rate was decreased at a high level of phenylalanine, 3.0% of the dry diet.

Animals↗
PubMed1984

Leucine, isoleucine and valine requirements of immature beagle dogs.

Three experiments were conducted with growing beagle dogs fed crystalline L-amino acid diets, to determine the requirement for each of the branched-chain amino acids: leucine, isoleucine and valine. Requirements were taken as the minimum dietary concentrations required for optimal growth, feed efficiency and nitrogen retention. For each amino acid, the requirements estimated from each of these criteria were similar. Ten- to 12-week-old male beagle dogs were found to require 0.65% leucine, 0.40% isoleucine and 0.43% valine. These values correspond to 159 mg leucine, 98 mg isoleucine and 105 mg valine per 100 kcal dietary metabolizable energy. These branched-chain amino acid requirements of the growing dog are lower than those of weanling rats or pigs.

Animals↗
PubMed1987

Isoleucine requirement of young growing male guinea pigs.

The isoleucine requirement of young, growing male guinea pigs was investigated by use of crystalline amino acid diets containing 3.65% nitrogen. Three-week-old guinea pigs were fed one of eight crystalline amino acid diets ranging from 0.2 to 1.2% isoleucine for 22 d. Diets were evaluated on the basis of body weight changes, nitrogen retention, carcass weight, liver weight, hematocrit, hemoglobin and carcass and liver weights expressed as percentages of live body weight. A 0.5% level of dietary isoleucine (2.2% of total nitrogen X 6.25) was the lowest level fed that did not have a response significantly lower than the higher levels fed, and that generally promoted a thrifty and well-groomed appearance of the animals.

Aging↗
PubMed1990

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

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, transport systems for the L-isomers of the amino acids. The average Michaelis-Menten constants were as follows: L-leucine, K1m = 0.17 mM, K2m = 6.5 mM; L-valine, K1m = 0.19 mM, K2m = 11.5 mM. The KA values were: L-leucine, K1A = 0.12 mM, K2A = 7.4 mM; L-valine, K1A = 0.18 mM, K2A = 10.0 mM; L-isoleucine, K1A = 0.17 mM, K2A = 9.0 mM. D-Leucine is taken up by a low-affinity system only (KA = 6.5 mM), which seems to be the same as the low-affinity system transporting the L-forms of the amino acids.

Amino Acids↗
PubMed2005

Exogenous isoleucine and fatty acid shortening ensure the high content of anteiso-C15:0 fatty acid required for low-temperature growth of Listeria monocytogenes.

Previous studies have demonstrated that the branched-chain fatty acid anteiso-C15:0 plays a critical role in the growth of Listeria monocytogenes at low temperatures by ensuring sufficient membrane fluidity. Studies utilizing a chemically defined minimal medium revealed that the anteiso fatty acid precursor isoleucine largely determined the fatty acid profile and fatty acid response of the organism to lowered growth temperature. When isoleucine was sufficient, the fatty acid profile was very uniform, with anteiso fatty acids comprising up to 95% of total fatty acid, and the major fatty acid adjustment to low temperature was fatty acid chain shortening, which resulted in an increase of anteiso-C15:0 solely at the expense of anteiso-C17:0. When isoleucine was not supplied, the fatty acid profile became more complex and was readily modified by leucine, which resulted in a significant increase of corresponding iso fatty acids and an inability to grow at 10 degrees C. Under this condition, the increase of anteiso-C15:0 at low temperature resulted from the combined effect of increasing the anteiso:iso ratio and chain shortening. A branched-chain alpha-keto acid dehydrogenase-defective strain largely lost the ability to increase the anteiso:iso ratio. Cerulenin, an inhibitor of beta-ketoacyl-acyl carrier protein synthase (FabF), induced a similar fatty acid chain shortening as low temperature did. We propose that the anteiso precursor preferences of enzymes in the branched-chain fatty acid biosynthesis pathway ensure a high production of anteiso fatty acids, and cold-regulated chain shortening results in a further increase of anteiso-C15:0 at the expense of anteiso-C17:0.

Base Sequence↗
PubMed1972

Isoleucine and threonine can prolong protein and ribonucleic acid synthesis in pyridoxine-starved mutants of Escherichia coli B.

Pyridoxineless mutants of Escherichia coli B stopped incorporation of nucleosides into trichloroacetic acid-insoluble material about 40 to 60 min after pyridoxine starvation was initiated, whereas incorporation of amino acids (measured the same way) slowed but did not stop for several hours. Both these incorporations and cell density were increased most effectively by the presence of either threonine or isoleucine. Arginine, glutamate, histidine, methionine, tryptophan, and tyrosine also caused significant but less dramatic increases. Inducibility of beta-galactosidase continued beyond the point where nucleic acids appeared to stop their synthesis, suggesting that messenger ribonucleic acid synthesis continued beyond ribosomal ribonucleic acid synthesis. This inducibility was also increased by isoleucine and threonine. The overall results suggest that the threonine-isoleucine biosynthetic pathway is the most sensitive to starvation for pyridoxine.

Amino Acids↗
PubMed1973

Effect of isoleucine, valine, or leucine starvation on the potential for formation of the branched-chain amino acid biosynthetic enzymes.

The derepression of the isoleucine and valine biosynthetic enzymes in Escherichia coli and Salmonella typhimurium was examined under conditions of restriction of isoleucine, valine, or leucine (the three amino acids needed for multivalent repression of these enzymes). A procedure was used that allowed the measurement of enzyme-forming potential that accumulated during the starvation period, but could not be expressed unless the missing amino acid was supplied. The threonine deaminase (the product of the ilvA gene)-forming potential that accumulated under such conditions was found to be unstable and decayed with a half-life of about 2.5 min (at 37 C). Evidence was obtained that indicates the threonine deaminase-forming potential that accumulates under conditions of isoleucine starvation is in the form of initiated (rifampin-resistant), but uncompleted (actinomycin D-sensitive), messenger ribonucleic acid chains. Furthermore, it appears that a large portion of the threonine deaminase- and dehydrase (the product of the ilvD gene)-forming potential, under such conditions, is in the form of initiated polypeptide chains. Based on these results and results obtained with SuA(-) strains, a model is presented that explains how the second gene (D) in the ilvADE operon can be partially transcribed and translated under conditions in which there are no completed messenger ribonucleic acids for the gene (A) transcribed before it.

Bacterial Proteins↗
PubMed1974

Isoleucine and valine metabolism in Escherichia coli K-12: detection and measurement of ilv-specific messenger ribonucleic acid.

Ribonucleic acid-deoxyribonucleic acid (RNA-DNA) hybridization was employed for the determination of messenger RNA transcribed from the ilv gene cluster of Escherichia coli K-12. Strains with derepressed levels of the isoleucine and valine biosynthetic enzymes owing to linked or unlinked genetic lesions were found to exhibit ilv messenger RNA levels from 1.5- to 4-fold higher than did their isogenic parents. When grown under conditions that specifically repressed the synthesis of isoleucine- and valine-forming enzymes, most strains exhibited drastically reduced ilv messenger RNA levels. Hybridization performed with the separated strands of ilv DNA showed that all the ilv genes are transcribed from the same strand, the "l strand" of lambdaphi80CI857St68dilv DNA. Sucrose gradient analyses of RNA extracted from cells starved for isoleucine, valine, or leucine resulted in the detection of at least two distinct types of ilv messenger RNA.

Centrifugation, Density Gradient↗
PubMed1975

Separate regulation of transport and biosynthesis of leucine, isoleucine, and valine in bacteria.

Since both transport activity and the leucine biosynthetic enzymes are repressed by growth on leucine, the regulation of leucine, isoleucine, and valine biosynthetic enzymes was examined in Escherichia coli K-12 strain EO312, a constitutively derepressed branched-chain amino acid transport mutant, to determine if the transport derepression affected the biosynthetic enzymes. Neither the iluB gene product, acetohydroxy acid synthetase (acetolactate synthetase, EC 4.1.3.18), NOR THE LEUB gene product, 3-isopropylmalate dehydrogenase (2-hydroxy-4-methyl-3-carboxyvalerate-nicotinamide adenine dinucleotide oxido-reductase, EC 1.1.1.85), were significantly affected in their level of derepression or repression compared to the parental strain. A number of strains with alterations in the regulation of the branched-chain amino acid biosynthetic enzymes were examined for the regulation of the shock-sensitive transport system for these amino acids (LIV-I). When transport activity was examined in strains with mutations leading to derepression of the iluB, iluADE, and leuABCD gene clusters, the regulation of the LIV-I transport system was found to be normal. The regulation of transport in an E. coli strain B/r with a deletion of the entire leucine biosynthetic operon was normal, indicating none of the gene products of this operon are required for regulation of transport. Salmonella typhimurium LT2 strain leu-500, a single-site mutation affecting both promotor-like and operator-like function of the leuABCD gene cluster, also had normal regulation of the LIV-I transport system. All of the strains contained leucine-specific transport activity, which was also repressed by growth in media containing leucine, isoleucine and valine. The concentrated shock fluids from these strains grown in minimal medium or with excess leucine, isoleucine, and valine were examined for proteins with leucine-binding activity, and the levels of these proteins were found to be regulated normally. It appears that the branched-chain amino acid transport systems and biosynthetic enzymes in E. coli strains K-12 and B/r and in S. typhimurium strain LT2 are not regulated together by a cis-dominate type of mechanism, although both systems may have components in common.

Acetolactate Synthase↗
PubMed1982

Altered regulation of isoleucine-valine biosynthesis in a hisW mutant of Salmonella typhimurium.

Control of isoleucine-valine biosynthesis was examined in the cold-sensitive hisW3333 mutant strain of Salmonella typhimurium. During growth at the permissive temperature (37 degrees C), the isoleucine-valine (ilv) biosynthetic enzyme levels of the hisW mutant were two- to fourfold below these levels in an isogenic hisW+ strain. Upon a reduction in growth temperature to partially permissive (30 degrees C), the synthesis of these enzymes in the hisW mutant was further reduced. However, synthesis of the ilv enzymes was responsive to the repression signal(s) caused by the addition of excess amounts of isoleucine, valine, and leucine to the hisW mutants. Such a "super-repressed" phenotype as that observed in this hisW mutant is similar to that previously shown for the hisU1820 mutant, but was different from the regulatory response of the hisT1504 mutant strain. Moreover, by the use of growth-rate-limiting amounts of the branched-chain amino acids, it was shown that this hisW mutant generally did not increase the synthesis of the ilv enzymes as did the hisW+ strain. Overall, these results are in agreement with the hypothesis that the hisW mutant is less responsive to ilv specific attenuation control than is the hisW+ strain and suggest that this limited regulatory response is due to an alteration in the amount or structure of an element essential to attenuation control of the ilv operons.

Acetolactate Synthase↗
PubMed1987

Acetohydroxy acid synthase I is required for isoleucine and valine biosynthesis by Salmonella typhimurium LT2 during growth on acetate or long-chain fatty acids.

Salmonella typhimurium LT2 normally expresses two acetohydroxy acid synthases (AHAS I and AHAS II). The function of AHAS I in this organism was unclear, since AHAS I-deficient (ilvBN) mutants of LT2 grew well on glucose or succinate minimal media, whereas AHAS II-deficient (ilvGM) mutants requried isoleucine for normal growth on glucose minimal media. We report that AHAS I-deficient mutants of S. typhimurium required isoleucine and valine for growth on acetate or oleate minimal media, whereas AHAS II-deficient mutants were able to grow on these media without isoleucine supplementation.

Acetates↗
PubMed1999

Role of bkdR, a transcriptional activator of the sigL-dependent isoleucine and valine degradation pathway in Bacillus subtilis.

A new gene, bkdR (formerly called yqiR), encoding a regulator with a central (catalytic) domain was found in Bacillus subtilis. This gene controls the utilization of isoleucine and valine as sole nitrogen sources. Seven genes, previously called yqiS, yqiT, yqiU, yqiV, bfmBAA, bfmBAB, and bfmBB and now referred to as ptb, bcd, buk, lpd, bkdA1, bkdA2, and bkdB, are located downstream from the bkdR gene in B. subtilis. The products of these genes are similar to phosphate butyryl coenzyme A transferase, leucine dehydrogenase, butyrate kinase, and four components of the branched-chain keto acid dehydrogenase complex: E3 (dihydrolipoamide dehydrogenase), E1alpha (dehydrogenase), E1beta (decarboxylase), and E2 (dihydrolipoamide acyltransferase). Isoleucine and valine utilization was abolished in bcd and bkdR null mutants of B. subtilis. The seven genes appear to be organized as an operon, bkd, transcribed from a -12, -24 promoter. The expression of the bkd operon was induced by the presence of isoleucine or valine in the growth medium and depended upon the presence of the sigma factor SigL, a member of the sigma 54 family. Transcription of this operon was abolished in strains containing a null mutation in the regulatory gene bkdR. Deletion analysis showed that upstream activating sequences are involved in the expression of the bkd operon and are probably the target of bkdR. Transcription of the bkd operon is also negatively controlled by CodY, a global regulator of gene expression in response to nutritional conditions.

Amino Acid Sequence↗
PubMed2006

Accumulation of homolanthionine and activation of a novel pathway for isoleucine biosynthesis in Corynebacterium glutamicum McbR deletion strains.

In the present work, the metabolic consequences of the deletion of the methionine and cysteine biosynthesis repressor protein (McbR) in Corynebacterium glutamicum, which releases almost all enzymes of methionine biosynthesis and sulfate assimilation from transcriptional regulation (D. A. Rey, A. Pühler, and J. Kalinowski, J. Biotechnol. 103:51-65, 2003), were studied. C. glutamicum ATCC 13032 DeltamcbR showed no overproduction of methionine. Metabolome analysis revealed drastic accumulation of a single metabolite, which was not present in the wild type. It was identified by isotopic labeling studies and gas chromatography/mass spectrometry as L-homolanthionine {S-[(3S)-3-amino-3-carboxypropyl]-L-homocysteine}. The accumulation of homolanthionine to an intracellular concentration of 130 mM in the DeltamcbR strain was accompanied by an elevated intracellular homocysteine level. It was shown that cystathionine-gamma-synthase (MetB) produced homolanthionine as a side reaction. MetB showed higher substrate affinity for cysteine (Km = 260 microM) than for homocysteine (Km = 540 microM). The cell is able to cleave homolanthionine at low rates via cystathionine-beta-lyase (MetC). This cleavage opens a novel threonine-independent pathway for isoleucine biosynthesis via 2-oxobutanoate formed by MetC. In fact, the deletion mutant exhibited an increased intracellular isoleucine level. Metabolic flux analysis of C. glutamicum DeltamcbR revealed that only 24% of the O-acetylhomoserine at the entry of the methionine pathway is utilized for methionine biosynthesis; the dominating fraction is either stored as homolanthionine or redirected towards the formation of isoleucine. Deletion of metB completely prevents homolanthionine accumulation, which is regarded as an important step in the development of C. glutamicum strains for biotechnological methionine production.

Bacterial Proteins↗
PubMed1968

Isoleucine and valine metabolism of Escherichia coli. XIV. Effect of thiaisoleucine.

Thiaisoleucine (2-amino-3-methylthiobutyrate) completely inhibited the growth of strain K-12 of Escherichia coli at a concentration of 5 x 10(-3)m. The inhibition was antagonized by growth-factor amounts of l-isoleucine. Thiaisoleucine inhibited the deamination of threonine and the transfer of (14)C-isoleucine to soluble ribonucleic acid and underwent transamination with alpha-ketoglutarate as the amino acceptor. In each case, the analogue appeared to be less effective than isoleucine as either an inhibitor or substrate.

Carbon Isotopes↗
PubMed2002

An isoleucine to leucine mutation in acetyl-CoA carboxylase confers herbicide resistance in wild oat.

Wild oat (Avena fatua L.) populations resistant to herbicides that inhibit acetyl-CoA carboxylase (ACCase; EC 6.4.1.2) represent an increasingly important weed control problem. The objective of this study was to determine the ACCase mutation responsible for herbicide resistance in a well-studied wild oat biotype (UMI). A 2039-bp region encompassing the carboxybiotin and acetyl-CoA binding domains of multifunctional plastidic ACCase was analyzed. DNA sequences representing three plastidic ACCase gene loci were isolated from both the resistant UMI and a herbicide-susceptible biotype, consistent with the hexaploid nature of wild oat. Only one nonsynonymous point mutation was found among the resistant wild oat sequences, inferring an isoleucine to leucine substitution. The position of this substitution corresponds to residue 1769 of wheat (Triticum aestivum L.) plastidic ACCase (GenBank accession No. AF029895). Analysis of an F2 population derived from a cross between a herbicide-resistant and a susceptible biotype confirmed co-segregation of herbicide resistance with the mutated ACCase. We conclude that the isoleucine to leucine mutation is responsible for herbicide resistance in UMI wild oat based on a comparison of the substitution site across species and ACCase types. While isoleucine is conserved among plastidic ACCases of herbicide-susceptible grasses, leucine is found in plastidic and cytosolic forms of multifunctional herbicide-resistant ACCase.

Acetyl-CoA Carboxylase↗