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)

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

A standard procedure for the identification of the N-terminal amino acid in N alpha-acylated proteins has been developed. After exhaustive proteolysis, the amino acids with blocked alpha-amino groups are separated from positively charged, free amino acids by ion exchange chromatography and subjected to digestion with acylase I. Amino acid analysis before and after the acylase treatment identifies the blocked N-terminal amino acid. A survey of acylamino acid substrates showed that acylase will liberate all the common amino acids except Asp, Cys or Pro from their N-acetyl-and N-butyryl derivatives, and will also catalyze the hydrolysis of N-formyl-Met and N-myristyl-Val. Thus, the procedure cannot identify acylated Asp, Cys or Pro, nor, because of the ion exchange step, N alpha-acyl-derivatives of Arg, Lys or His. Whenever the protease treatment releases free acylamino acids, the remaining amino acids should be detected. When applied to several proteins, the procedure confirmed known N-terminal acylamino acids and identified acyl-Ser in enolases from chum and coho salmon muscle and in pyruvate kinase from rabbit muscle, and acyl-Thr in phosphofructokinase from rabbit muscle. The protease-acylase assay has been used to identify blocked peptides from CNBr- or protease-treated proteins. When such peptides were treated with 1 N HCl at 110 degrees for 10 min, sufficient yields of deacylated, mostly intact, peptide were obtained to permit direct automatic sequencing. The N-terminal sequences of rabbit muscle and coho salmon enolase were determined in this way and are compared to each other and to the sequence of yeast enolase.
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PMID:Studies on N alpha-acylated proteins: the N-terminal sequences of two muscle enolases. 391 71

l-Threonine deaminase (l-threonine dehydratase [deaminating], EC 4.2.2.16) has been shown to be involved in the regulation of three of the enzymes of isoleucine-valine biosynthesis in yeast. Mutations affecting the affinity of the enzyme for isoleucine also affected the repression of acetohydroxyacid synthase, dihydroxyacid dehydrase, and reductoisomerase. The data indicate that isoleucine must be bound for effective repression of these enzymes to take place. In a strain with a nonsense mutation midway in liv 1, the gene for threonine deaminase, starvation for isoleucine or valine did not lead to derepression of the three enzymes; starvation for leucine did. The effect of the nonsense mutation is recessive; it is tentatively concluded, therefore, that intact threonine deaminase is required for derepression by two of the effectors for multivalent repression, but not by the third. A model is presented which proposes that a regulatory species of leu tRNA(leu) is the key intermediate for repression and that threonine deaminase is a positive element, regulating the available pool of charged leu tRNA by binding it.
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PMID:Involvement of threonine deaminase in repression of the isoleucine-valine and leucine pathways in Saccharomyces cerevisiae. 457 Jul 83

Threonine deaminase from a mutant of Escherichia coli growing alternatively with isoleucine or pyridoxine is a dimer, whereas the wild-type enzyme is a tetramer.
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PMID:Threonine deaminase from a mutant requiring isoleucine or pyridoxine: inability to form a tetrameric state. 459 57

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

N alpha-Acyl amino acid releasing enzyme (NAARE), an enzyme cleaving acetylMet-Ala at the Met-Ala bond was purified from rat brain cytosol to apparent homogeneity by salt precipitation, gel filtration, and several steps of ion exchange. Levels of NAARE exceeded acylase measured with acetylmethionine in all brain regions and subcellular fractions examined: 60% was associated with cytosol and the remainder with debris or the crude nuclear and mitochondrial-synaptosomal subfractions. Activity was highest in pituitary and was approximately 0.5-0.6 that of liver or kidney. The purified enzyme preferentially hydrolyzed acetylmethionyl peptides: Km for acetylMet-Ala was 0.93; Vmax, 3.5 nmol-1 (kcat, 1185) with pH optimum of 8.9 as compared with 8.2 for acylases measured in cytosol. The purified enzyme was devoid of acylase and common exo- and endopeptidase contamination. Structure-activity relationships examined with synthetic formylated or acetylated peptides indicated no significant effects for di- or tripeptides if the second substituent was Ala, Ser, Asn, or Thr, but the activity was reduced 0.5-fold for Leu, a branched-chain amino acid. No hydrolysis was observed for polypeptides with five or more residues having N-terminal acetylated Tyr (enkephalin) or Ser (alpha-melanocyte-stimulating hormone, thymosin alpha 1), supporting the notion that the enzyme plays a role only in turnover of smaller peptides formed perhaps as a result of endopeptidase cleavage of proteins or polypeptides containing acetylated Met at the N terminus.
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PMID:Observations on N alpha-deacetylation of model amino acids and peptides: distribution and purification of a specific N-acyl amino acid releasing enzyme in rat brain. 686 20

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


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