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PubMed1979

Regulation of the threonine operon: tandem threonine and isoleucine codons in the control region and translational control of transcription termination.

The DNA sequence of 178 base pairs preceding the first structural gene of the threonine operon of Escherichia coli has been determined. A region of perfect 2-fold rotational symmetry, involving 28 base pairs, precedes the first structural gene. The structural similarity of this sequence to known RNA polymerase termination sites suggests that this region is the termination site of the threonine operon leader RNA. Moreover a mutation (thr 79-20), which confers a depressed, constitutive phenotype, was sequenced and found to be a G.C insertion in the putative terminator. A potential coding region for a 21-amino acid leader peptide ends approximately 18 base pairs before the terminator. This peptide contains eight threonine and four isoleucine codons. Eleven of these codons are in tandem. A model for threonine operon regulation, involving alternative secondary RNA structures and translation of leader RNA, is discussed.

Base Sequence↗
PubMed1983

Threonine metabolism in sheep. 2. Threonine catabolism and gluconeogenesis in pregnant ewes.

The irreversible loss rate (ILR) of glucose, bicarbonate and threonine were determined in six twin- and triplet-bearing ewes on three occasions during the last 6 weeks of gestation. Three of the ewes (group S) were given conventional rations of hay plus concentrates so that their blood ketone levels did not rise over this period. The other three ewes (group H) were given a fixed intake of hay throughout; their blood ketone levels rose, but remained at subclinical levels. The results are presented in the form of three-pool open-compartment models for each period. There was an increase in the glucose ILR for both groups over the 6-week period, but the over-all increase (mean +/- SE) was much greater (P less than 0.001) in group S (35.1 +/- 2.43 g carbon/d) than in group H (11.3 +/- 1.28 g C/d). Similarly, increases in bicarbonate ILR were also higher in group S (161 +/- 11.2 g C/d) than in group H (63 +/- 21.7 g C/d). However, whereas with group S ewes, receiving supplementary feed, this increase was progressive throughout the 6 weeks, with the group H ewes the increase which occurred over the last 3 weeks of gestation (56 +/- 26.3 g C/d) was much greater than that which occurred over the preceding 3 weeks (7 +/- 4.7 g C/d). This pattern was also evident in the oxidation of glucose to CO2. In contrast to the previously mentioned findings, neither threonine ILR nor the amount of threonine converted to glucose or catabolized to CO2 changed significantly over the 6-week period. The results are discussed in the light of findings presented in the previous paper that the amount of threonine used in catabolic processes can alter if a glucose-only sink is created in wether sheep.

3-Hydroxybutyric Acid↗
PubMed1996

Characterization of an Arabidopsis thaliana cDNA encoding an S-adenosylmethionine-sensitive threonine synthase. Threonine synthase from higher plants.

An Arabidopsis thaliana cDNA encoding an S-adenosylmethionine-sensitive threonine synthase (EC 4.2.99.2) has been isolated by functional complementation of an Escherichia coli mutant devoid of threonine synthase activity. Threonine synthase from A. thaliana was shown to be synthesized with a transit peptide. The recombinant protein is activated by S-adenosylmethionine in the same range as the plant threonine synthase and evidence is presented for an involvement of the N-terminal part of the mature enzyme in the sensitivity to S-adenosylmethionine.

Amino Acid Sequence↗
PubMed1986

Evolution of biosynthetic pathways: a common ancestor for threonine synthase, threonine dehydratase and D-serine dehydratase.

The Bacillus subtilis genes encoding threonine synthase (thrC) and homoserine kinase (thrB) have been cloned via complementation of Escherichia coli thr mutants. Determination of their nucleotide sequences indicates that the thrC stop codon overlaps the thrB start codon; this genetic organization suggests that the two genes belong to the same operon, as in E. coli. However, the gene order is thrC-thrB in B. subtilis whereas it is thrB-thrC in the thr operon of E. coli. This inversion of the thrC and thrB genes between E. coli and B. subtilis is indicative of a possible independent construction of the thr operon in these two organisms. In other respects, comparison of the predicted amino acid sequences of the B. subtilis and E. coli threonine synthases with that of Saccharomyces cerevisiae threonine dehydratase and that of E. coli D-serine dehydratase revealed extensive homologies between these pyridoxal phosphate-dependent enzymes. This sequence homology, which correlates with similarities in the catalytic mechanisms of these enzymes, indicates that these proteins, catalyzing different reactions in different metabolic pathways, may have evolved from a common ancestor.

Amino Acid Sequence↗
PubMed1993

pH-dependent decarboxylation of 2-amino-3-ketobutyrate, the unstable intermediate in the threonine dehydrogenase-initiated pathway for threonine utilization.

2-Amino-3-ketobutyrate can be readily formed enzymatically by the action of L-threonine dehydrogenase. A convenient assay for determining the half-life of this beta-keto acid is afforded by its rapid and quantitative conversion to glycine (+ acetyl CoA), as catalyzed by 2-amino-3-ketobutyrate CoA lyase. Using this system, we have found the half-life of 2-amino-3-ketobutyrate varies with pH from 8.6 minutes at pH 5.9 to 140 minutes at pH 11.1 yielding a theoretical titration curve that predicts a pKa value of 8.15 for the alpha-amino group of this intermediate. These data are considered relevant to discussions pertaining to a threonine dehydrogenase/2-amino-3-ketobutyrate CoA lyase enzyme complex in the threonine utilization pathway and to mechanistic aspects of the 5-aminolevulinate synthase-catalyzed reaction where 2-amino-3-ketoadipate is involved.

5-Aminolevulinate Synthetase↗
PubMed2006

Autoprocessing of Helicobacter pylori gamma-glutamyltranspeptidase leads to the formation of a threonine-threonine catalytic dyad.

Helicobacter pylorigamma-glutamyltranspeptidase (HpGT) is a glutathione-degrading enzyme that has been shown to be a virulence factor in infection. It is expressed as a 60-kDa inactive precursor that must undergo autocatalytic processing to generate a 40-kDa/20-kDa heterodimer with full gamma-glutamyl amide bond hydrolase activity. The new N terminus of the processed enzyme, Thr-380, is the catalytic nucleophile in both the autoprocessing and enzymatic reactions, indicating that HpGT is a member of the N-terminal nucleophile hydrolase superfamily. To further investigate activation as a result of autoprocessing, the structure of HpGT has been determined to a resolution of 1.9 A. The refined model contains two 40-kDa/20-kDa heterodimers in the asymmetric unit and has structural features comparable with other N-terminal nucleophile hydrolases. Autoprocessing of HpGT leads to a large conformational change, with the loop preceding the catalytic Thr-380 moving >35 A, thus relieving steric constraints that likely limit substrate binding. In addition, cleavage of the proenzyme results in the formation of a threonine-threonine dyad comprised of Thr-380 and a second conserved threonine residue, Thr-398. The hydroxyl group of Thr-398 is located equidistant from the alpha-amino group and hydroxyl side chain of Thr-380. Mutation of Thr-398 to an alanine results in an enzyme that is fully capable of autoprocessing but is devoid of enzymatic activity. Substrate docking studies in combination with homology modeling studies of the human homologue reveal additional mechanistic details of enzyme maturation and activation, substrate recognition, and catalysis.

Binding Sites↗
PubMed2003

The rapid anorectic response to a threonine imbalanced diet is decreased by injection of threonine into the anterior piriform cortex of rats.

Rats quickly recognize and reject diets deficient in an essential amino acid. The purpose of this study was to determine whether the anterior piriform cortex (APC), the site traditionally recognized as the amino acid chemosensor, plays a role in this early behavior. Rats had cannulae implanted bilaterally into the APC, and were injected with either saline vehicle or 2 nmoles of threonine (n = 6 per group). All rats were then fed a diet imbalanced with respect to threonine. The threonine-injected group had first meals of longer duration and consumed more food. These data conformed to expectations derived from earlier studies of responses to the first meal of an amino acid imbalanced diet. We conclude that the concentration of the dietary limiting amino acid in the APC regulates acceptance and rejection of amino acid deficient diets.

Amino Acids↗
PubMed2004

Potential for protein deposition and threonine requirement of modern genotype barrows fed graded levels of protein with threonine as the limiting amino acid.

The study was conducted to estimate the actual genetic potential for daily protein deposition of growing barrows [genotype: Piétrain x (Duroc x Landrace)]. Twenty-four pigs with an average initial body weight (BW) of 43.7 +/- 0.7 kg were used in a N-balance study. Semi-purified diets with graded levels of crude protein (45.8, 94.2, 148.0, 198.9, 255.5 and 300.2 g/kg DM) were used, based on a constant mixture of wheat, soya bean protein concentrate and potato protein concentrate as protein sources. The amino acid pattern of the diets was according to the ideal amino acid ratio for growing pigs (Wang and Fuller, 1989), with the exception of threonine (adjusted as limiting amino acid). N-balance data were used to estimate daily N-maintenance requirement (NMR = 446 mg N/BW0.67 kg/day) by regression method and the theoretical maximum of daily N-retention (PDmaxT = 3115 mg N/BW0.67 kg/day) based on N-utilization model of Gebhardt (1966) using program Mathematica 3.0. The results indicate that PDmaxT of pigs under study is much higher than results from earlier studies with older genotypes. In summary, pigs of modern genotype have a very high genetic potential for daily protein deposition and these actual data are important basic informations for estimation of amino acid requirement within the model used. Threonine requirement data depending on threonine efficiency and protein deposition (8.96, 10.45 and 12.22 g/day for 130, 145 and 160 g daily protein deposition; 50 kg body weight) are discussed.

Animal Feed↗
PubMed1971

Minor threonine dehydratase encoded within the threonine synthetic region of Bacillus subtilis.

Challenging auxotrophs on metabolites that are precursors of a biosynthetic step involving a mutated enzyme has revealed a new class of suppressor mutations which act by derepressing a minor enzyme activity not normally detected in the wild-type strain. These indirect, partial suppressor mutations which allow isoleucine auxotrophs to grow on homoserine or threonine have been analyzed to determine their effect on enzymes involved in the biosynthesis of these amino acids. It has been found that one class of these suppressor mutations (sprA) leads to the derepression of homoserine kinase, homoserine dehydrogenase, and a minor threonine dehydratase that is not sufficiently active to be detected in the wild-type strain. The gene encoding this second threonine dehydratase activity has been found to be located between the structural genes for homoserine kinase and homoserine dehydrogenase. The results of these experiments indicate that plating of auxotrophs on precursors of a biosynthetic step involving mutated enzymes could prove to be a valuable method for the detection of regulatory mutants as well as a possible tool in studying the evolution of biochemical pathways.

Bacillus subtilis↗
PubMed1999

Increased intracellular calcium in rat anterior piriform cortex in response to threonine after threonine deprivation.

The anterior piriform cortex (APC) may serve as the chemosensor for amino acid (AA) deficiency in rats. To investigate the mechanism by which the APC recognizes a limiting indispensable AA (IAA), we examined changes in intracellular calcium ([Ca2+]i) in APC slices after culture in medium with or without threonine (Thr) or lysine (Lys). The addition of 1 or 10 mM Thr to slices previously incubated in Thr-devoid medium resulted in a significant and sustained increase in [Ca2+]i compared to control slices; an effect not seen when isoleucine, another IAA, was added. Similar results were seen when lysine, but not threonine, was added to slices incubated in lysine-devoid medium. The rise in [Ca2+]i resulting from the addition of the limiting IAA to deficient slices may be linked to enhanced activity of the appropriate AA transporter. This is suggested by preliminary findings that serine, a small neutral AA that uses the same transporter as threonine, gave rise to an enhanced response in the Thr-deficient slice.

Analysis of Variance↗
PubMed1977

Threonine-sensitive homoserine dehydrogenase and aspartokinase activities of Escherichia coli K12. Kinetic and spectroscopic effects upon binding of serine and threonine.

The two threonine-sensitive activities aspartokinase and homoserine dehydrogenase are inhibited by L-serine. The inhibition of the aspartokinase by L-serine displays homotropic cooperative effects and is competitive versus aspartate. The inhibition by L-serine of the homoserine dehydrogenase displays Michaelis-Menten kinetics which are of a competitive nature versus homoserine. Characteristic effects of L-serine on the protein include a perturbation of its absorption and fluorescence spectra, with an increase in the fluorescence of the protein-NADPH complex. L-serine shifts the allosteric equilibrium of the protein to a "T-like" conformation to which L-threonine binds noncooperatively. L-Serine, a threonine analog, is not capable, as the physiological effector, of inducing a complete R to T transition of the enzyme; the aspartokinase globules show a cooperative conformation change upon serine binding, but this conformation change is not found in the homoserine dehydrogenase globules.

Aspartokinase Homoserine Dehydrogenase↗
PubMed1996

O-phospho-DL-threonine and O-phospho-L-threonine compared with their serine analogs.

In crystals of O-phospho-DL-threonine and O-phospho-L-threonine, the molecules are zwitterions HO3-POCH-(CH3)CH(NH3+)CO2H linked by three-dimensional networks of strong P-O-H...O = P, C-O-H...O = P, N-H...O = P and N-H...O = C hydrogen bonds with (O...O) = 2.55 (3) A and (N...O) = 2.84 (4) A. Both the molecular conformations and the nearest-neighbor hydrogen-bonded surroundings are very similar in the racemic and enantiomeric crystals of the threonine compounds, but earlier studies of crystals of the analogous serine compounds have shown that the serine zwitterions HO3-POCH2CH(NH3+)CO2H have different conformations about the C beta-O gamma-P phosphate ester bonds and different hydrogen-bonded surroundings.

Crystallization↗
PubMed1981

[Cholecystokinin-pancreozymin synthesis. Synthesis of [28-threonine,31-norleucine]- and [28-threonine,31-leucine]cholecystokinin-pancreozymin-(25-33)-nonapeptide].

The syntheses of two analogues related to the C-terminal nonapeptide amide sequence 25-33 of cholecystokinin-pankreozymin are described. Based on the primary structure of the CCK-PZ-active caerulein and the experiences gained from the methionine replacement with leucine or norleucine in human little gastrin I, the analogues were designed by substituting methionine 28 with threonine, and methionine 31 with leucine and norleucine, respectively. Using a new method for the synthesis of tyrosine-O-sulfate-containing peptides, developed in our laboratory, and applying acid-labile side-chain protection in combination with the benzyloxycarbonyl group, the fully protected nonapeptide amide derivatives Z-Arg(Z2)-Asp(OBut)-Tyr-(SO3Ba1/2)-Thr(But)-Gly-Trp-Leu-Asp(OBut)-Phe-NH2 and Z-Arg(Z2)-Asp(OBut)-Tyr(SO3-Ba1/2)-Thr(But)-Gly-Trp-Nle-Asp(OBut)-Phe-NH2, were obtained. Upon hydrogenolytic and subsequent acidolytic removal of the protecting groups, followed by purification via chromatographic procedures the nonapeptide amides were isolated in satisfactory yields at a high degree of purity. In vivo and in vitro assays showed that a substitution of methionine 31 by norleucine with concomitant replacement of methionine 28 by threonine produced a fully active analogue, whereas for the threonine 28, leucine 31 analogue the pankreozymin-activity was lowered by a factor 10.

Amino Acid Sequence↗
PubMed1987

A kinetic method for distinguishing whether an enzyme has one or two active sites for two different substrates. Rat liver L-threonine dehydratase has a single active site for threonine and serine.

We have elaborated a kinetic method which allows us to evaluate whether a Michaelis-Menten-type enzyme acting on two different substrates has one or two active sites. This method has been used with the rat liver L-threonine dehydratase, which catalyzes the dehydrative deamination of both serine and threonine. The experimental data can be fitted to the theoretical plot obtained for the case of a single active site.

Animals↗
PubMed2003

Thin layer chromatographic resolution of some 2-arylpropionic acid enantiomers using L-(-)-serine, L-(-)-threonine and a mixture of L-(-)-serine and L-(-)-threonine-impregnated silica gel as stationary phases.

Impregnated silica TLC plates with L-(-)-serine and L-(-)-threonine and a mixture of L-(-)-serine and L-(-)-threonine (1:1) as chiral selectors were prepared to use as chiral stationary phases (CSPs) in thin layer chromatography. The resolution of the enantiomers of 2-arylpropionic drugs, including ibuprofen, ibuproxam, ketoprofen, pranoprofen, benoxaprofen, flurbiprofen and tiaprofenic acid was investigated on these CSPs. A mobile phase system of acetonitrile-methanol-water (16:4:0.5, v/v/v) was used. The spots were detected with iodine vapours and the detection limits were found to range between 0.25 and 0.5 micro g/mL for all racemic compounds investigated. The effect of temperature, pH and concentration of the impregnating chiral selectors on resolution has been studied.

Chromatography, Thin Layer↗
PubMed1999

Rapid fall in plasma threonine followed by increased intermeal interval in response to first ingestion of a threonine-devoid diet in rats.

In most animals, ingestion of a diet lacking an essential amino acid (EAA) gives rise to anorexia within a few hours. The first signal in this feeding response may be the fall in plasma levels of the limiting EAA. In the present study, we measured plasma amino acid levels and food intake after the first exposure to either a threonine-devoid (THR-DEV) or corrected (COR) diet in 16 rats bearing a chronic jugular catheter for blood sampling. Food intake was reduced 165 min (p<0.05) after presentation of the THR-DEV diet. Analysis of the feeding pattern showed that intake was reduced via a four-fold lengthening of the second inter-meal interval. Plasma threonine levels started to fall between 30 and 60 min after onset of the meal (p<0.05). These results, observed in the same rats, lend further support for an early modification of the plasma amino acid pattern in relation to the decrease in feeding of a diet that is EAA deficient.

Analysis of Variance↗