Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.1.1.3 (HSD)
 3,464 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

S-2-Aminoethyl cysteine (AEC) reduced both growth rate and final growth level of Serratia marcescens Sr41. The growth inhibition was completely reversed by lysine. AEC inhibited the activity of lysine-sensitive aspartokinase to a lesser extent than lysine. The AEC addition to the medium lowered not only the level of lysine-sensite aspartokinase but also those of homoserine dehydrogenase and threonine deaminase, whereas lysine repressed the aspartokinase alone. To select mutations releasing lysine-sensitive aspartokinase from feedback controls, AEC-resistant colonies were isolated from strains HNr31 and HNr53, both of which were previously found to excrete threonine on the minimal plates but not on the plates containing excess lysine. Two of 280 resistant colonies excreted large amounts of threonine. Strains AECr174 and AECr301, derived from strains HNr31 and HNr53, respectively, lacked both feedback inhibition and repression of lysine-sensitive aspartokinase. These strains produced about 7 mg of threonine per ml in the medium containing glucose and urea.
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PMID:Participation of lysine-sensitive aspartokinase in threonine production by S-2-aminoethyl cysteine-resistant mutants of Serratia marcescens. 23 91

Reduction in the amounts of activity of the first enzyme, aspartokinase (EC 2.7.2.4) and two branch-point enzymes, dihydrodipicolinic acid synthase (EC 4.2.1.52) and homoserine dehydrogenase (EC 1.1.1.3), located in the pathway for the synthesis of aspartate-family amino acids, occurred when cell suspension cultures of Daucus carota L. var. Danvers were grown in media containing 2 mM threonine or 2 mM lysine, endproducts of the pathway. Activity of the lysine-sensitive form of aspartokinase was decreased when cells were grown in medium containing lysine and the activity of the threonine-sensitive form was decreased when cells were grown in medium containing threonine. Activity of the branch-point enzyme leading to threonine synthesis, homoserine dehydrogenase, was decreased up to 70% in specific activity (units/mg protein) and relative activity (units/g fresh weight) when cells were grown in media containing lysine or threonine. Threonine had no effect on the relative activity of dihydrodipicolinic acid synthase, but decreased its specific activity. Lysine decreased the relative activity of the synthase by up to 40%, but had little effect on its specific activity. The decreased activities of the enzymes were apparently not due to binding of the inhibitory amino acids to the enzymes since homogenization of cells in buffer with 2 mM lysine and threonine did not decrease the measurable enzyme activities. These and other results presented suggest that both forms of the aspartokinase activity and homoserine dehydrogenase activity can be altered by supplementing the growth medium with lysine or threonine.
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PMID:Expression of aspartokinase, dihydrodipicolinic acid synthase and homoserine dehydrogenase during growth of carrot cell suspension cultures on lysine- and threonine-supplemented media. 23 96

2-Amino-4-oxo-5-chloropentanoic acid inactivates specifically the homoserine dehydrogenase activity of the bifunctional enzyme, aspartokinase I--homoserine dehydrogenase I. The aspartokinase activity remains essentially untouched and retains its threonine sensitivity. The inactivation of the dehydrogenase requires the covalent binding of one equivalent of the analogue per subunit. Alkylation does not affect the tetrameric state of the protein. The alkylating agent, a substrate analogue, meets the qualitative and quantitative requirements of an affinity label.
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PMID:The threonine-sensitive homoserine dehydrogenase and aspartokinase activities of Escherichia coli K12. Specific inactivation of the homoserine dehydrogenase activity by the affinity label, 2-amino-4-oxo-5-chloropentanoic acid. 23 85

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.
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PMID:Threonine-sensitive homoserine dehydrogenase and aspartokinase activities of Escherichia coli K12. Kinetic and spectroscopic effects upon binding of serine and threonine. 32

beta-Hydroxynorvaline (alpha-amino-beta-hydroxyvaleric acid)-resistant mutants of Serratia marcescens deficient in both threonine dehydrogenase and threonine deaminase were isolated and characterized. One of the mutants, strain HNr21, lacked feedback inhibition of threonine-sensitive aspartokinase and homoserine dehydrogenase, was repressed for the two enzymes, and produced 11 mg of threonine per ml of medium containing a limiting amount of isoleucine. The other mutant, strain HNr59, was constitutively derepressed for aspartokinase and homoserine dehydrogenase. Its kinase was sensitive to feedback inhibition, but its dehydrogenase was insensitive to feedback inhibition. This strain produced 5 mg of threonine per ml of medium containing either a limiting or an excess amount of isoleucine. Diaminopimelate auxotrophs derived from strain HNr59 produced more threonine (13 mg/ml) than the parent strain. However, similar auxotrophs derived from strain HNr21 produced the same amount of threonine as that produced by the parent strain.
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PMID:Threonine production by regulatory mutants of Serratia marcescens. 35 Jan 54

A fine structure analysis of the threonine operon in Escherichia coli K-12 was performed by deletion mapping. Lambda transducing bacteriophages carrying various parts of the threonine operon were isolated from strains in which the lacZ gene was fused to a thr gene. We tested for recombination between deletions of the threonine promotor extending into the threonine operon, carried by the phage, and bacterial thr auxotrophs. The relative order of thrO (operator) mutations was established. We propose that an operator region is located between a promoter region and the structural genes. Mutations leading to the desensitization of the aspartokinase I-homoserine dehydrogenase I towards threonine were localized in two different regions of the thrA gene.
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PMID:Fine structure analysis of the threonine operon in Escherichia coli K-12. 35 21

Mutants, resistant to threonine analogue, DL-alpha-amino-beta-hydroxyvaleric acid, were obtained after the treatment of Escherichia coli K-12 RelA- cells with nitrosoguanidine, and among them the strain with maximal threonine production (about 3g/l) was selected. Genetic and biochemical analysis of the producer has revealed the dependency of the threonine production on at least three mutations. The mutation in the thrA gene disturbs retroinhibition of homoserine dehydrogenase by threonine. The mutation in the ilvA gene decreases the activity of threonine deaminase, and thus results in partial isoleucine auxotrophy, and finally, the reversion in the relA gene restores the stringent amino acid control of RNA synthesis in threonine producer cells. The role of relA gene in threonine production was demonstrated by comparing pairs of strains differing from one another in the allelic state of the relA gene. The level of threonine synthesis (its intra- and extracellular concentrations) during moderate isoleucine starvation in RelA+ cells 2-3 times as high as in RelA- cells. The presence of relA+ allele is found to result in the increase of the cell resistance to DL-alpha-amino-beta-hydroxyvaleric acid.
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PMID:[Gene relA function in the expression of amino acid operons. II. Effect of the allelic state of gene relA on the overproduction of threonine by an Escherichia coli K-12 mutant resistant to beta-hydroxynorvaline]. 35 57

A threonine-producing strain of Serratia marcescens Sr41 was constructed according to the following process. Thr- strain E-60 was derived from strain HNr59 having constitutive levels of threonine-sensitive aspartokinase and homoserine dehydrogenase. Thr+ transductant T-570 was constructed from strain E-60 and phage grown on strain HNr21 having feedback-resistant threonine-sensitive aspartokinase and homoserine dehydrogenase. This transductant lacked both feedback inhibition and repression for the two enzymes. Thr- strain N-11 was derived from strain AECr174 lacking feedback inhibition and repression of lysine-sensitive aspartokinase. Subsequently, the threonine region of strain T-570 was transduced into strain N-11. One of the THR+ transductants, strain T-693, produced markedly high levels of the two aspartokinases and homoserine dehydrogenase, which were insensitive to feedback inhibition. This strain produced about 25 mg of threonine per ml in the medium containing sucrose and urea.
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PMID:Transductional construction of a threonine-producing strain of Serratia marcescens. 39 67

A detailed physicochemical characterization of purified homoserine dehydrogenase of Rhodospirillum rubrum is presented. The enzyme has a molecular weight of 110000 and consists of two subunits of identical molecular weight of 55000. Depending on the ionic strength and protein concentration it is possible for the native enzyme to dimerize to produce an enzymatically active species of molecular weight 220000. Titrations of the native and detergent-treated enzyme with a variety of sulfhydryl reagents show 2 mol free--SH groups per 110000 g, one of which is buried in the protein interior. L-Threonine and/or high concentrations of salt can expose the buried--SH group, and this--SH group is essential for the catalytic activity of the enzyme. Two independent lines of evidence show that extensive polymerization of the enzyme caused by L-threonine and/or high concentrations of salt does not involve the formation of intermolecular disulfide bonds.
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PMID:Homoserine dehydrogenase of Rhodospirillum rubrum. Physical and chemical characterization. 41 12

Homoserine dehydrogenase in unpurified extracts of maize (Zea mays L.) cell suspensions is inhibited 73% by the feedback regulator threonine; the remaining 27% of the total activity is not affected even by high concentrations of threonine. The threonine-resistant and threonine-sensitive homoserine dehydrogenase activities were separated by affinity chromatography on Blue Sepharose columns, and the two distinct homoserine dehydrogenases were purified. The threonine-resistant enzyme is an Mr = 70,000 dimer of two Mr = 38,000 subunits and the threonine-sensitive enzyme is an Mr = 190,000 dimer containing two apparently different subunits with molecular weights of 89,000 and 93,000. The threonine-resistant enzyme exhibits normal Michaelis-Menten kinetics and its activity is not affected by any of the amino acid end products of the aspartate pathway. The threonine-sensitive enzyme exhibits positive cooperative kinetics with respect to NADPH and is inhibited by threonine and stimulated by isoleucine. All attempts to affect interconversion of the two purified enzymes have been unsuccessful. Because the purified enzymes correspond to activities present in crude extracts of various maize tissues, it is concluded that the two types of homoserine dehydrogenase are natural in vivo constituents of maize.
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PMID:Isolation and characterization of two homoserine dehydrogenases from maize suspension cultures. 76 32


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