Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.5.1.4 (deaminase)
5,113 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Kinetic analysis of the biosynthetic threonine deaminase, EC 4.2.1.16, from Samonella typhimurium yields hyperbolic substrate saturation curves in the absence of, and higher order substrate saturation curves in the presence of, L-isoleucine. L-Valine reverses this effect of L-isoleucine by restoring the hyperbolic substrate saturation curves. The inhibition of enzyme activity and the reversal of valine stimulation is a function of a second order concentration of L-isoleucine, whereas antagonism of inhibition is a function of first order concentration of valine. The antagonistic effects on enzyme activity of L-isoleucine and of L-valine appear as competitive in diagnostic plots. Threonine deaminase possesses two L-isoleucine binding sites (Kd equals 3.6 muM) and one L-valine binding site (Kd equals 26 muM); the binding of these ligands appear competitive. Exclusion of L-valine requires the binding of 2 molecules of L-isoleucine whereas binding of a single L-valine molecule prevents the binding of 2 L-isoleucine molecules. Cooperative binding of L-isoleucine is not observed under any of the conditions tested. Two cases, expressed in terms of modified Adair equations and based upon the assumption that L-threonine also serves as an activator ligand which binds to the L-valine site, are presented. Case I states that liganding of the activator sites must percede substrate-binding at the active site, and Case II states that the activator site liganding is required solely for reactivation of the L-isoleucine-inhibited enzyme. Analysis of kinetic data by a curve-fitting process suggests that Case II described the relationship between the activator site and the L-isoleucine sites. An enzymatically inactive derivative of threonine deaminase, prepared by reduction with borohydride, binds isoleucine and valine in a manner similar to native holoenzyme. Binding of L-threonine and L-valine to the derivatized enzyme is competitive. The Kd for threonine binding is 3 mM, which is in excellent agreement with the Kd determined by the curve fitting process. It is concluded that the modulation of threonine deaminase activity is wrought by interaction between inhibitor sites and an activator site rather than inhibitor and active sites and that induced transitions rather than concerted transitions more adequately describe the underlying regulatory principle.
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PMID:Threonine deaminase from Salmonella typhimurium. Relationship between regulatory sites. 108 62

In confirmation of the findings of Gaitonde et al. (1974), a decrease in the brain concentration of threonine and serine, and an increase in glycine, were observed in rats maintained on a thiamin-deficient diet. Similar changes were found in the blood, and the concentration of several other amino acids in the blood decreased significantly. There was a correlation between the concentrations of threonine, serine, aspartate and asparagine in the brain and blood. In experiments in which [U-14C]threonine was injected into rats most of the radioactivity in the brain and blood of control rats was, as expected, in threonine in the acid soluble metabolites. In contrast, a considerable proportion of radioactivity was also found in other amino acids, namely glutamate, glutamine, aspartate, gamma-aminobutyrate and alanine, in the brain of thiamin-deficient rats. [U-14C]Threonine was also converted into 14C-labelled lactate and glucose, but the extent of this conversion was severalfold higher in thiamin-deficient than in control rats. This finding gave evidence of the stimulation in thiamin-deficient rats of the catabolism of [U-14C]threonine to [14C]lactate by the aminoacetone pathway catalysed by threonine dehydrogenase, and into succinate via propionate by the alpha-oxobutyrate pathway catalysed by threonine dehydratase (deaminase). The measurement of specific radioactivities of glutamate, aspartate and glutamine after injection of [U-14C]threonine, indicated a stimulation of the activities of threonine dehydrogenase and threonine dehydratase (deaminase) in the brain of thiamin-deficient rats. The specific radioactivities of glutamate, asparatate and glutamine int he brain were consistent with an alteration in the metabolism of threonine, mainly in the 'large' compartment of the brain of thiamin-deficient rats. The measurement of relative specific radioactivity of proteins after injection of [U-14C]threonine indicated a marked decrease in the synthesis of proteins, mainly in the liver of thiamin-deficient rats.
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PMID:Conversion of [U-14C]threonine into 14C-labelled amino acids in the brain of thiamin-deficient rats. 118 Sep 21

The glycoprotein nature of the binding subunit of the dopamine D2 receptor in rat striatum has been examined by photoaffinity labeling receptor preparations with N-(p-azido-m-[125I]iodophenethyl)spiperone followed by treatment of crude membrane receptor or receptor fractions isolated from sodium dodecyl sulfate (SDS) polyacrylamide gels with endo- and exoglycosidases. The major photoaffinity labeled protein migrates as a heterogeneous species on 10% SDS polyacrylamide gels and ranges from 130,000 to 75,000 relative molecular mass (Mr). This heterogeneity can be explained by glycosylation of the receptor by complex-type N-linked oligosaccharides. Three fractions of labeled receptor were isolated from SDS polyacrylamide gels over a range of 130,000 to 75,000 Mr; after digestion with peptide-N4-[N-acetyl-beta-glucosaminyl] asparagine amidase, all fractions yielded a single peptide approximately 40,000 Mr. Treatment of photoaffinity labeled membranes with alpha-mannosidase was without effect. The dopamine D2 receptor appears to contain substantial amounts of sialic acid as treatment of photoaffinity labeled membranes with neuraminidase increased the receptor mobility on SDS polyacrylamide gels to a species of 50,000-54,000 Mr. Treatment of the receptor with neuraminidase followed by endo-alpha-N-acetylgalactosaminidase did not change the electrophoretic migration pattern from that seen after neuraminidase treatment alone, suggesting that the binding peptide contains no serine- or threonine-linked oligosaccharides. A smaller binding peptide of approximately 31,000 Mr is also apparent in crude photoaffinity labeled membranes. This material also contains N-linked oligosaccharide. Complete removal of N-linked oligosaccharide from the dopamine D2 receptor did not change the rank order potency of agonist and antagonist compounds to compete for [3H]spiperone binding to crude membrane fractions. The dopamine D2 receptor represents a highly glycosylated neural receptor.
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PMID:N-linked oligosaccharides are responsible for rat striatal dopamine D2 receptor heterogeneity. 252 26

The catabolic L-serine (L-threonine) deaminase of Saccharomyces cerevisiae allows the yeast to grow on media with L-serine or L-threonine as sole nitrogen source. A mutant, cha1 (catabolism of hydroxyamino acids), lacking this enzyme activity has been isolated. We have cloned the CHA1 gene by complementation of a cha1 mutation. Northern analysis showed that CHA1 mRNA has a size of about 1200 ribonucleotides. CHA1 is probably the structural gene for the enzyme; it is an abundant RNA in cells grown with serine and threonine as nitrogen source, whereas it is not detected when cells are grown on ammonium or proline, i.e., the transcription of the CHA1 gene is induced by serine or threonine. Under induced growth conditions haploid ilv1 CHA1 strains do not require isoleucine, i.e., the catabolic deaminase is able to substitute for the biosynthetic threnonine deaminase encoded by the ILV1 gene. We have identified a nuclear, recessive mutation, sil1, that suppresses ilv1 mutations by increased transcription of the CHA1 gene under growth conditions leading to partial induction. The sil1 mutation could exert its effect by increasing the effective pools of the hydroxyamino acids. Alternatively SIL1 may encode a negatively acting regulatory protein for CHA1.
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PMID:Molecular genetics of serine and threonine catabolism in Saccharomyces cerevisiae. 284 Nov 85

Threonine deaminase (l-threonine dehydratase EC 4.2.1.16) has been partially purified from a new extreme thermophilic bacterium, Thermus X-1, which is similar to T. aquaticus YT-1. The threonine deaminase of strain X-1 has a maximal rate of reaction at 85 to 90 C and is more thermostable than the threonine deaminase from mesophilic bacteria. The enzyme has an apparent molecular weight of 100,000 to 115,000, a K(m) for l-threonine of 14 mM, a pH optimum of 8.0, and like other threonine deaminases also catalyzes the deamination of serine. However the Thermus X-1 threonine deaminase does not show a strong feedback inhibition by isoleucine. It is suggested that the regulation of the biosynthesis of isoleucine in this extreme theromophile may resemble that reported in Rodospirillum rubrum.
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PMID:Purification and properties of threonine deaminase from the X-1 isolate of the genus Thermus. 470 89

The levels of the five enzymes required for isoleucine and valine synthesis were examined under several growth conditions in strain K-12 of Escherichia coli and mutants derived from it. In strains with wild type repressibility, the same pattern of derepression was found on limiting isoleucine as is found to be constitutive in strain Tir-8, which has an altered isoleucine-activating enzyme. Homoserine dehydrogenase, which is essential for the biosynthesis of threonine and is normally derepressed on limiting isoleucine or threonine, is also derepressed in strain Tir-8. Threonine deaminase and homoserine dehydrogenase were partially repressed in strain Tir-8 by very high levels of isoleucine, but were not further derepressed over levels in minimal medium by limiting isoleucine.
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PMID:Isoleucine and valine metabolism of Escherichia coli. XVI. Pattern of multivalent repression in strain K-12. 487 Feb 82

Saccharomyces cerevisiae mutants lacking the anabolic L-threonine deaminase, the ilv1- mutants, have been found to exhibit a normal ability to grow, without auxotrophy towards isoleucine, on L-threonine of L-serine as only nitrogen nutrient. Starting from a strain carrying a ilv1- mutation, a new mutation affecting the ability to utilize L-threonine as nitrogen source was selected. This mutation, which also impairs the ability to utilize L-serine, has been denominated cha-, for 'catabolism of hydroxyamino acids' and was found to result in the lack of a catabolic L-serine (L-threonine) deaminase. This enzyme which, unlike the anabolic threonine deaminase, is more active towards serine than towards threonine, differs from the latter enzyme by a number of biochemical and regulatory properties. Whereas the anabolic enzyme is an allosteric enzyme sensitive to feedback inhibition by isoleucine, the catabolic enzyme exhibits Michaelian kinetics: no control of its activity has been detected. Its synthesis is induced by L-serine and L-threonine. These two enzymes, which thus can be easily differentiated by means of their regulations, display a limited ability to compensate for one another's absence and appear to play clearly distinct roles under normal physiological conditions.
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PMID:Occurrence of a catabolic L-serine (L-threonine) deaminase in Saccharomyces cerevisiae. 704 46

Crystallographic analysis and site-directed mutagenesis have been used to identify the catalytic and oligosaccharide recognition residues of peptide-N4-(N-acetyl-beta-D-glucosaminyl)asparagine amidase F (PNGase F), an amidohydrolase that removes intact asparagine-linked oligosaccharide chains from glycoproteins and glycopeptides. Mutagenesis has shown that three acidic residues, Asp-60, Glu-206, and Glu-118, that are located in a cleft at the interface between the two domains of the protein are essential for activity. The D60N mutant has no detectable activity, while E206Q and E118Q have less than 0.01 and 0.1% of the wild-type activity, respectively. Crystallographic analysis, at 2.0-A resolution, of the complex of the wild-type enzyme with the product, N,N'-diacetylchitobiose, shows that Asp-60 is in direct contact with the substrate at the cleavage site, while Glu-206 makes contact through a bridging water molecule. This indicates that Asp-60 is the primary catalytic residue, while Glu-206 probably is important for stabilization of reaction intermediates. Glu-118 forms a hydrogen bond with O6 of the second N-acetylglucosamine residue of the substrate and the low activity of the E118Q mutant results from its reduced ability to bind the oligosaccharide. This analysis also suggests that the mechanism of action of PNGase F differs from those of L-asparaginase and glycosylasparaginase, which involve a threonine residue as the nucleophile.
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PMID:Active site and oligosaccharide recognition residues of peptide-N4-(N-acetyl-beta-D-glucosaminyl)asparagine amidase F. 749 89

Tyrosine 121, a residue located in a alpha-helical polypeptide segment of glucosamine 6-phosphate deaminase from Escherichia coli, has recently been proposed to have a role in the binding of the allosteric activator N-acetyl-D-glucosamine 6-phosphate. Accordingly, the site-directed mutants Tyr 121-Thr and Tyr 121-Trp were constructed, to assess experimentally the role of Tyr 121 in the allosteric function of the enzyme. The kinetic study of both mutant forms revealed that the replacements caused striking changes in allosteric activator binding and allosteric properties, when compared to the wild-type enzyme. While the wild-type deaminase behaves as a classical allosteric K-system which can be described by the allosteric concerted model, both mutant forms present an asymmetric behavior toward the allosteric activator, which can be described as two distinct half-of-the-sites allosteric activation steps occurring with different affinities for the N-acetyl-D-glucosamine 6-phosphate. During the first (high affinity) activation phase, the mutant forms of deaminase behave as mixed K/V allosteric enzyme. The biphasic activation curve was also demonstrated by direct binding measurements of the 14C-labeled activator to Tyr 121-Trp and Tyr 121-Thr deaminases. The kinetic analysis of these mutant forms also showed that the threonine replacement produced an important distortion of the enzyme structure reflected in a considerable decrease of its catalytic efficiency.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Asymmetric allosteric activation of Escherichia coli glucosamine-6-phosphate deaminase produced by replacements of Tyr 121. 774 11

1. The Brown Norway (B/N) Katholiek rat is a mutant strain of plasma kininogen deficiency. The plasma of B/N-Katholiek rats was shown to contain only 3-5% of high-molecular-weight and low-molecular-weight kininogens (HK and LK) of the normal level by specific RIA, and 30% of prekallikrein was detected by amidase activity. However, HK antigen in the liver microsomal fraction of B/N-Katholiek rats was about 60% of that of normal rats. 2. In this paper we compare and discuss synthesis and secretion of HK and LK by primary cultures of livers of deficient and normal rats. The deficient hepatocytes could synthesize HK and LK in the same way as normal cells but could not secrete mature forms of HK and LK in the medium. Examination of the subcellular localization of the mutant HK in the hepatocytes showed that a larger amount of mutant HK antigen, compared to normal rats, was found in the 10,000 g fraction, which is rich in lysosomes, suggesting that the mutant HK may be transported to the lysosomes. 3. We also analyzed sequence of the HK cDNA of B/N-Katholiek and B/N-Kitasato rats and found a point mutation of G to A at nucleotide 487, which locates at the heavy chain region of HK and LK. 4. We constructed five expression plasmids to transfect COS-1 cells to examine HK secretion. COS-1 cells transfected with the plasmids containing the G to A transition could not secrete and retained HK, while those cells transfected with the plasmids containing normal G released HK into the medium. 5. These results indicate that a point mutation G to A at nucleotide 487, resulting in an amino acid transition from alanine (163) to threonine, is responsible for the defective secretion of HK and LK by the liver of B/N-Katholiek rats. We also discuss other cases of secretion defect of plasma proteins reported in the literature.
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PMID:Molecular mechanism of kininogen deficiency in brown Norway Katholiek rats. 774 70


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