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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Native dimeric methionyl-tRNA synthetase and its monomeric proteolytic fragment are shown to form and to bind 1 mol of methyionyl adenylate per polypeptide chain. Moreover, at 25 degrees C, each monomer of the dimeric native enzyme behaves independently, exhibiting the same parameters for the methionine activation reaction as does the monomeric modified enzyme. These results were obtained using several independent methods including equilibrium and nonequilibrium dialysis, active site and tryptophan fluorescence titrations, and stopped-flow by fluorescence. Stopped-flow resolution of the reversible methionine activation reaction also demonstrates that methionine and ATP-Mg2+ react without coupling to form a ternary enzyme-methionine-ATP-Mg2+ complex. This complex readily converts to enzyme-methionyl approximately adenylate-PP-Mg2+ with a standard free energy close to zero. It is concluded that the uncoupled enzyme-methionine-ATP-Mg2+ complex may resemble the transition state of the reaction at the expense of the additional state of the reaction at the expense of the additional synergistic binding energy provided by reciprocal coupling, within the site, of the methionine molecule with the adenosine and PP-Mg2+ parts of the ATP-Mg2+ molecule (Blanguet, S., Fayat, G., and Waller, J. P. (1975), J. Mol. Biol. 94, 1.).
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PMID:Methionyl-tRNA synthetase from Escherichia coli: active stoichiometry and stopped-flow analysis of methionyl adenylate formaiton. 18 14

Control of the levels of cAMP in the early phase after addition of catecholamines and the effect of insulin is discussed under consideration of own findings from experiments with isolated fat cells of the rat. Data on the kinetics of cAMP are interpreted in the light of results from several groups of a rapid activation of phosphodiesterase activity along with the adenylate cyclase system. Comparison of energy metabolism of fat cells with the formation of cAMP under conditions of near-maximal activation of the adenylate cyclase system by isoproterenol shows that about half of the cellular ATP turnover is used for information transfer. Insulin reduces cAMP concentrations in the presence of isoproterenol within one min of incubation when added either together with or after the catecholamine. Experiments with propranolol and the phosphodiesterase inhibitor, methyl isobutylxanthine suggest an effect of insulin on formation and breakdown of cAMP.
Mol Cell Endocrinol
PMID:Hormonal control of cyclic AMP turnover in isolated fat cells. 18 81

The influence of tRNA on the kinetics of PP-ATP exchange and aminoacyl-tRNA formation catalysed by leucyl-, phenylalanyl-, and tryptophanyl-tRNA synthetases has been investigated. These enzymes were chosen because they belong to three main classes of quaternary structure alpha1, alpha2beta2 and alpha2, respectively. The present paper shows that the investigated synthetases manifest kinetic cooperativity of the active centres which is negative in the case of AAA formation and positive in the case of leucyl- and tryptophanyl-tRNA synthesis. The obtained data were interpreted with the aid of the trigger model of the enzyme.
Mol Biol Rep 1976 Jul
PMID:Interaction of aminoacyl-tRNA synthetases and tRNA: positive and negative cooperativity of their active centres. 18 1

An investigation was made of the effect of NAD+ analogues on subunit interactions in yeast and rabbit muscle glyceraldehyde 3-phosphate dehydrogenases by using the subunit exchange (hybridization) method described previously [e.g. see Osborne & Hollaway (1975) Biochem. J. 151, 37-45]. The ligands ATP, ITP, ADP, AMP, cyclic AMP and ADP-ribose like NADH, all caused an apparent weakening of intramolecular subunit interactions, whereas NAD+ caused an apparent increase in the stability of the tetrameric enzyme molecules. A mixture of NMN and AMP, although it did not simulate completely the NAD+-induced 'tightening' of the enzyme structure, did result in a more than 20-fold decrease in the rate of subunit exchange compared with that in the presence of AMP alone. These results show that occupancy of the NMN subsite of the enzyme NAD+-binding site is insufficient in itself to give the marked tightening of the enzyme structure induced by NAD+. The 'tightening' effect is specific in that it seems to require a phosphodiester link between NMN and ADP-ribose. These effects are discussed in terms of the detailed X-ray structure of the lobster holoenzyme [Buehner et al. (1974) J. Mol. Biol. 90, 25-49].
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PMID:An investigation of the nicotinamide-adenine dinucleotide-induced 'tightening' of the structure of glyceraldehyde 3-phosphate dehydrogenase. 18 44

1. The pyruvate dehydrogenase complex from human heart has been partially purified and shown to be regulated by a phosphorylation-dephosphorylation cycle similar to that previously found for other mammalian tissues. 2. Incubation of the complex with ATP (2 mmol/1) led to its inactivation associated with the concomitant incorporation into the protein of 32P from the terminal phosphate group of the ATP. Pyruvate, ADP, thiamin pyrophosphate and dichloroacetate diminished the rate of inactivation by ATP. 3. Pyruvate dehydrogenase phosphatase from human heart requires Mg2+ for activity and is sensitive to Ca2+ at concentrations of a few mumol/1. Similar ionic requirements of the skeletal muscle phosphatase have been demonstrated in a crude tissue extract. 4. The activity of pyruvate dehydrogenase in human adipose tissue was less than 10% of typical values in rats. This could be due to the high level of dietary fat consumed by humans, which is known to repress the enzyme activity in rats.
Clin Sci Mol Med 1976 Nov
PMID:Regulation of the human pyruvate dehydrogenase complex. 18 26

In two fractions obtained from the bovine A. coronaria adenylate cyclase activity was identified and characterized. The adenylate cyclase activity of the 75,000 X g sediment shows a pH optimum at 7.4. The temperature dependence of this adenylate cyclase activity is linear when represented in the Arrhenius plot, and an Arrhenius activation energy of 13.2 kcal Mol-1 can be calculated for the enzyme reaction. The Km-value of the enzyme to ATP is 6 +/- 0.6 - 10(-4) M. The adenylate cyclase activity of the 75,000 X g sediment can be stimulated by NaF. 5'AMP and adenosine inhibit the adenylate cyclase activity of the 75,000 X g sediment. With regard to the enzyme activity, Mn++ and Co++ replace Mg++, but not Ca++. The monovalentcations Na+ and K+ do not influence the adenylate cyclase activity. In a particulate fraction containing plasma membranes, adenylate cyclase activity was also identified. This adenylate cyclase activity can be stimulated by catecholamines, noradrenaline, and isoproterenol. This stimulation can, however, only be proved for the enzyme in the coronaries of 9-week-old and 2-year-old animals. The adenylate cyclase activity from the coronaries of adult animals is not affected by catecholamines. These findings are discussed with regard to hypertension frequently found in adult animals.
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PMID:[Proof of adenylate cyclase activity in the coronary artery of cattle]. 19 28

Cyclic AMP (300 micron) activates phosphofructokinase from dialyzed haemolysates of mature rat erythrocytes. The main conclusions are: a) Cyclic AMP, at pH 7.1 and low concentrations of fructose-6-phosphate, is able to reverse the inhibition produced by different amounts of ATP (up to 1.5 mM). b) The cyclic nucleotide is a positive allosteric effector of the enzyme as shown by the displacement of sigmoidal fructose-6-phosphate saturation curve to hyperbolic kinetics in the presence of inhibitory concentrations (1.5 mM) of ATP.c) Cyclic AMP has no significant influence as deinhibitor of phosphofructokinase either at pH 7.1 and non-inhibitory levels (0.25 mM) of ATP or at pH 8.1 and inhibitory (1.5 mM) or non-inhibitory (0.25 mM) concentrations of ATP. Similar conclusions were obtained with 300 micron AMP but not at a lower concentration (3 micron) with both nucleotides. The comparison of cyclic AMP result with those obtained under similar concentrations of AMP suggest that cyclic AMP is really only an "in vitro" modulator of the enzyme from rat erythrocytes, presumably at an AMP regulatory stie, since non-physiological concentrations are required to act as deinhibitor.
Mol Cell Biochem 1977 May 03
PMID:Activation of rat erythrocyte phosphofructokinase by AMP and by non-physiological concentrations of cyclic AMP. 19 80

Incubation of cells from a wild type strain of E. coli with 0.3 mg/ml rifampicin for 15 minutes lead to a complete inhibition of RNA synthesis measured as the uracil incorporation into the trichloroacetic acid insoluble fraction. In these rifampicin-treated cells [14C]uracil incorporation tended to decrease during a further incubation at 37 degrees. Addition of cyclic AMP increased the inactivation of the system responsible for [14C]uracil uptake. The cyclic nucleotide effect seems to be specific since ATP or 5'AMP did not increase such inactivation.
Mol Cell Biochem 1977 Jul 05
PMID:Influence of cyclic 3',5'-adenosine monophosphate on uracil uptake by rifampicin treated Escherichia coli cells. 19 84

The catalytic groups, involved in aminoacyl-tRNA formation remain unknown. The isolation and identification of an active covalent complex between the enzyme and substrate is an essential step in understanding the reaction mechanism. We identified and isolated the covalent complex of tryptophanyl-tRNA synthetase (EC 6.1.1.2) and tryptophane which was able to aminoacylate the tRNATrp in the absence of ATP. In beef pancreas tryptophanyl-tRNA synthetase preparations, isolated by the previously described method, a tightly bound tryptophan was revealed which could not be removed by charcoal treatment, by gel-filtration and by replacement with the excess of typtamine, a competitive inhibitor of tryptophane. This tightly bound tryptophane is able to exchange rapidly and specifically with radioactive tryptophane allowing to obtain [14C]tryptophane-tryptophanyl-tRNA synthetase complex. After the reaction of this complex with NH2OH at neutral pH tryptophanyl hydroxamate is formed proving the activated state of the tryptophane in the initial complex with the enzyme. No nucleotide impurites were noticed in the enzyme preparation; the complex is stable at denaturation. A conclusion is made that the tryptophanyl-tRNA synthetase isolated by our method is a tryptophanyl-enzyme. The tryptophanyl residue could be specifically transferred to tRNATrp in the absence of other substrates of the reaction, the efficiency of the transfer does not exceed 25%. The content of the covalently bound tryptophane never exceeds 1 mole per mole of the dimeric enzyme. The total content of tryptophane in the forms of tryptophanyl-enzyme and tryptophanyl adenylate enzyme complex equals 2 moles per mole of the enzyme. The tryptophanyl-enzyme is destroyed during incubation with AMP or with pyrophosphate. The role of the tryptophanyl-enzyme as a possible intermediate in the course of aminoacylation of tRNATrp is discussed.
Mol Biol (Mosk)
PMID:[Tryptophanyl tRNA synthetase: isolation and characteristics of the tryptophanyl-enzyme]. 20 77

It was shown that chromatin isolated from the liver of adult rats is an effective cell-free system for studying DNA synthesis without using exogenous enzymes or DNA-template. Both replication synthesis initiated in vivo and unscheduled synthesis activated several fold after gamma-irradiation of isolated chromatin proceed in chromatin preparations. Unscheduled synthesis consists of template-dependent and template-independent synthesis. Template-dependent synthesis proceeds with a maximum rate in the presence of all four deoxynucleoside triphosphates (dNTP). Template-independent synthesis proceeds with an appearable maximum rate in the presence of one dNTP whose incorporation is inhibited by the addition of the rest dNTP. All three DNA synthesis in chromatin are ATP-dependent. Replication synthesis but not the unscheduled one is inhibited by actinomycin D and N-ethylmaleinimide. Repair inhibitor--0.01 M caffeine--suppresses the initiation of unscheduled synthesis, but does not influence its elongation. The incubation conditions of chromatin for unscheduled synthesis are optimalized as for temperature, pH, time of incubation, qualitative ionic composition of the medium, concentration of chromatin, ATP, dNTP, MgCl2, NaCl. Michaelis constants for TTP are equal to 1 mM for template-independent synthesis and 3 mM for template-dependent synthesis. At optimal conditions DNA of chromatin is lengthened by 8 X 10--3% as the result of template-dependent synthesis and by 1 X 10--3% as the result of template-independent. The transition from nuclei to chromatin as well as the purification of chromatin from nuclear membranes enhance the rate of unscheduled synthesis. On the other hand, addition of nucleoplasm or cell extract to the chromatin does not considerably influence the synthesis. So it is suggested that the enzymes of initiation and elongation of unscheduled DNA synthesis are concentrated in the chromatin. The plausible role of unscheduled synthesis in excision and postreplication repair of eukaryotic DNA is discussed.
Mol Biol (Mosk)
PMID:[Endogenous DNA synthesis in isolated chromatin]. 20 78


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