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

1. The hepatic concentration of several nucleotides and metabolites was measured during the first few minutes after an intravenous load of fructose to mice. The first changes, observed at 30s, were a decrease in the concentration of Pi and a simultaneous accumulation of fructose 1-phosphate. The decrease in the concentrations of ATP and GTP proceeded more slowly. An increase in the concentration of IMP was detected only after 1 min and could therefore not be considered to be the cause of the accumulation of fructose 1-phosphate. 2. To explain the temporary burst of adenine nucleotide breakdown that occurs after a load of fructose, the kinetics of AMP deaminase (EC 3.5.4.6) from rat liver were reinvestigated at physiological (0.2 mM) concentration of substrate. For this purpose, a new radiochemical-assay procedure was developed. At 0.2mM-AMP a low activity could be measured, which was more than 90% inhibited by 5mM-Pi. ATP (3MM) increased the enzyme activity over 200-fold. Pi alone did not influence the ATP-activated enzyme, but 0.5mM-GTP caused a 60% inhibition. The combined effect of both inhibitors at their physiological concentrations reached 95%. 3. It is proposed that the rapid degradation of adenine nucleotides that occurs after a load of fructose is caused by a decrease in the concentration of both inhibitors, Pi and GTP, soon counteracted by the decrease in the concentration of ATP. 4. Some of the kinetic parameters of liver AMP deaminase were computed in terms of the concerted transition theory of Monod, Wyman & Changeux (1965) (J. Mol. Biol. 12, 88-118).
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PMID:The mechanism of adenosine triphosphate depletion in the liver after a load of fructose. A kinetic study of liver adenylate deaminase. 86 6

Highly purified plasma membranes were obtained from isolated porcine thyroid cells maintained in conditions of culture in the presence of thyrotropin (stimulated cells) or in their absence (non-stimulated cells). Analyses of both types of membranes by high-resolution sodium dodecylsulfate-polyacrylamide slab gel electrophoresis showed reproducible quantitative differences in protein bands of apparent molecular weight 38,000, 36,000 and inconstantly 96,000. Phosphorylation of membranes by [gamma-32P]ATP was 2-3 times higher in membranes from thyrotropin-stimulated than in membranes from non-stimulated cells. About 20 32P-labeled bands were detected by slab gel electrophoresis in denaturing conditions, among which the catalytic subunit of Na+, K+ ATPase was characterized. In addition, plasma membranes from thyrotropin-stimulated cells contained a firmly bound [14C]glucosamine-containing glycoprotein probably related to an aggregation-promoting factor. 125I-labeled thyroglobulin and components of unknown nature were associated with plasma membranes from thyrotropin-stimulated cells. Whether they participate in the structure and function(s) of the plasma membrane or represent contaminants of the preparation is not clear at the present time.
Mol Cell Endocrinol 1977 Jun
PMID:Thyrotropin-induced plasma membrane protein modifications in porcine thyroid cells. 88 86

The rates of tryptophanyl-tRNA formation catalyzed by beef pancreas tryptophanyl-tRNA synthetase were measured in a concentration range of each substrate (tryptophan, ATP and yeast tRNATrp) and also in the presence of various concentrations of substrate analogues (tryptamine and alpha,beta-methylene analogue of ATP) concentrations. The data obtained were compared with the kinetic equations which described various possible mechanisms of the reaction. The comparison of the mechanisms was based on the calculation of relative probabilities of each hypothesis the efficiency of which was demonstrated earlier. The calculations have shown that two mechanisms according to which the intermediate enzyme-aminoacyl-adenylate complex formation involves the enzyme-aminoacyl-tRNA complex are the most probable ones.
Mol Biol (Mosk)
PMID:[The mechanism of the reaction forming tryptophanyl-tRNA, catalyzed by tryptophan:tRNA-ligase]. 94 May 60

By measuring the specific radioactivity of glucose released from isolated perfused livers of normal, fed rats in the presence of [U-14C]fructose, the gluconeogenetic and glycogenolytic contributions to glucose production were estimated. After 20 min of perfusion with 4 mM fructose, glycogenolysis was inhibited by 40% in the absence and by 70% in the presence of glucagon (3 nM). Glucagon decreased the release of lactate plus pyruvate and enhanced glucose formation from fructose without affecting its uptake. Glycerol (4 mM) and xylitol (3 mM) had qualitatively similar, but smaller effects on glucagon-stimulated glycogenolysis. The glucagon-mediated phosphorylase b to a conversion was not altered by fructose, indicating that glycogenolysis was decreased as a consequence of an inhibition of phosphorylase a. During the first minutes after the addition of fructose, decreased ATP/AMP ratios and tissue Pi levels correlated with a transient increase of phosphorylase a activity. It was concluded that the effects of fructose on the control of hepatic glycogenolysis and glucose production were the result of a complex interplay between a transient b to a conversion of phosphorylase and an inhibition of the a-form of the enzyme, possibly by fructose 1-phosphate and other phosphorylated metabolites.
Mol Cell Endocrinol 1976 Nov
PMID:Interactions of glucagon and fructose in the control of glycogenolysis in perfused rat liver. 100 7

1. The regulatory properties of two interconvertible kinetic forms of class A pyruvate kinase from Ehrlich ascites tumor cells have been studied with a partially purified enzyme preparation free of interfering enzymatic activities. 2. The hyperbolic form shows Michaelis-Menten kinetics for P-pyruvate, with high affinity for this substrate and low affinity for the inhibitory amino acids alanine and phenylalanine. The sigmoidal form displays positive cooperativity respect to P-pyruvate (n=1.4), with lower affinity for this substrate and higher affinity for the inhibitory amino acids. 3. The equilibrium between the hyperbolic and the sigmoidal forms of the enzyme is affected by substraetes and effectors. P-pyruvate, ADP and Fru-P2 shift the equilibrium to the hyperbolic form while ATP, alanine and phenylalanine stabilize the sigmoidal form. 4. Effector metabolites affect the molecular weight of the protein, acting on an equilibrium between dimers and tetramers. P-pyruvate and ADP associate the enzyme to a tetramer while ATP, alanine and phenylalanine favor the occurrence as a dimer. The positive modifier Fru-P2 did not associate the enzyme to the tetramer, even at 1 mM concentration. 5. A tentative molecular model for pyruvate kinase A on the basis of the kinetic and aggregation interconversion is proposed.
Mol Cell Biochem 1976 Oct 30
PMID:Interconversion phenomena between two kinetic forms of class a pyruvate kinase from Ehrlich ascites tumor cells. 100 94

Reaction rates for ATP-PPi isotope exchange (vex) and tryptophanyl-tRNA formation (vaa) catalysed concomitantly in one incubation mixture by beef pancreas tryptophanyl-tRNA synthetase (trsase) have been examined as a function of substrate concentrations. Comparison of the vex/vaa ratio found experimentally with the ratio predicted theoretically conforms the mechanism suggested earlier and permits to describe it in more detail. I. At least two reaction routes exist in which an ATP-PP: exchange is allowed. These routes are interconnected with each other via the stage at which tRNA binds to the enzyme. 2. In both these routes the low molecular weight substrates bind with enzyme in the order ATP first, tryptophan second. 3. Enzyme-aminoacyladenylate complex is an intermediate in the reaction of aminoacyl-tRNA formation. Pyrophosphate is detached from the enzyme prior to tRNA. 4. The enzyme releases AMP and tryptophanyl-tRNA in a random fashion. All the aformentioned properties are common both for trigger mechanism and Yarus-Berg mechanism which up to now were considered in literature independently.
Mol Biol (Mosk)
PMID:[Kinetic model describing the action of tryptophanyl-tRNA-synthetase]. 105 75

Microsomes isolated from the fibroin region of the Bombyx mori silkgland synthesize in the cell-free system a glycin rich polypeptide or polypeptides presumably representing fibroin precursors. Besides microsomes the system requires ATP and ATP-generating system, GTP, soluble protein fraction and tRNA, glycine incorporation is inhibited by puromycin and cycloheximide. It is shown that the synthesis of a polypeptide with high Gly/Lys ratio requires soluble protein fraction isolated from the silk gland at the end of the instar V. When the soluble protein fraction from the larvoe at the early instar V is used the Gly/Lys ratio in the product is markedly lower. These results permit to suggest that fibroin synthesis may be regulated at the level of tRNA aminoacylation.
Mol Biol (Mosk)
PMID:[Properties of the cell-free protein synthesizing system from the fibroin region of the Bombyx mori silkgland]. 105 90

1. Methionine adenosyltransferase (ATP:L-methionine-S-adenosyl transferase, EC 2.5.1.6), cystathionine beta-synthase F1L-serine hydro-lyase (adding homocysteine), EC 4.2.1.22] and cystathionine gamma-lyase [L-cystathionine cysteine-lyase (deaminating), EC 4.4.1.1] activities were found only in the cytosol fraction of rat liver cells. None was found in the mitochondrial or endoplasmic reticulum fractions as judged by the distribution of marker enzymes on a density gradient after centrifugation of the cytoplasmic fraction of a liver homogenate, or in a preparation of liver cell nuclei. 2. Polymorphs, lymphocytes (with admixed monocytes) and mixed bone marrow white cells contained no methionine adenosyl transferase, cystathionine beta-synthase or cystathionine gamma-lyase activities. 3. The possible bearing of these results on the problem of abnormal cystine storage in cystinosis is briefly discussed.
Clin Sci Mol Med Suppl 1975 Jun
PMID:Methionine adenosyltransferase, cystathionine beta-synthase and cystathionine gamma-lyase activity of rat liver subcellular particles, human blood cells and mixed white cells from rat bone marrow. 105 81

1. Two women with severe hypokalaemic alkalosis were investigated by means of muscle biopsy before and at the end of 2 and 3 weeks respectively of intense therapy with potassium chloride. 2. The muscle biopsy material was analysed for water, electrolytes, adenine nucleotides, phosphocreatine, free creatine, pyruvate, lactate, glycogen and free amino acids. The extra- and intra-cellular distribution of water, electrolytes and amino acids was calculated by the chloride method. 3. Both patients showed a marked loss of intracellular potassium and an increase in intracellular sodium concentration. The muscle magnesium content was also slightly decreased. After repletion with potassium chloride, muscle sodium and potassium became normal. 4. The contents of creatine phosphate, ATP, ADP, AMP, lactate and pyruvate were within normal limits, but the phosphocreatine/total creatine ratio was reduced. After repletion, a small change in the apparent creatine-phosphokinase equilibrium had occurred, suggesting a minor increase in intracellular pH. 5. The concentrations of the basic amino acids, lysine, arginine and ornithine were increased far above normal. The intracellular accumulation of arginine was much higher than the increase in lysine concentration and histidine concentration was normal. This differs from findings in potassium-depleted rats, where the intracellular lysine concentration is much higher than arginine concentration and histidine is high as well. After potassium repletion the intracellular concentration of ornithine, lysine and arginine became normal in one case and decreased considerable in the other. An increased intracellular concentration of glutamate and glutamine was also observed after potassium repletion.
Clin Sci Mol Med 1976 Dec
PMID:Influence of severe potassium depletion and subsequent repletion with potassium on muscle electrolytes, metabolites and amino acids in man. 107 Apr 23

The conformational changes in aspartate transcarbamylase upon binding of substrates or regulatory ligands and the effects of alterations in the subunit structure on the allosteric interactions are reviewed. The available information including recent results from studies of the c3r6 complex (c denotes the catalytic polypeptide and r, the regulatory polypeptide) is considered in terms of the existing models for the discrepancies between experimental observations and the present models could be resolved by postulating an important role for r:r interactions in the allosteric mechanism. A new model is presented in which an obligatory conformational change upon binding of substrates results in an alteration in the relative orientation of c versus r. As a consequence of symmetry conservation, the r:r domain is shifted to a position of higher potential energy. By favoring one or the other alternative r:r domains, CTP and ATP can respectively enhance and reduce the sigmoidal character of substrate saturation. The model is shown to be consistent with all of the important known properties of the enzyme. Because the heterotropic effects of CTP or ATP are postulated to operate via a mechanism separate from that for the homotropic effects of the substrates, this model accounts satisfactorily for the observation by Kerbiriou and Herve (Kerbiriou, D., and Herve, G. (1973) J. Mol. Biol. 78, 687-702) that homotropic effects can be abolished whereas heterotropic effects are retained in the altered enzyme from Escherichia coli grown in the presence of 2-thiouracil.
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PMID:Subunit interactions in aspartate transcarbamylase. A model for the allosteric mechanism. 108 47


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