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Query: HUMANGGP:021133 (ATP)
 132,114 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two rabbit erythrocyte casein kinases, GTP:casein kinase I and GTP:casein kinase II, have been purified 29 000- and 47 000-fold, respectively. Studies employing sucrose density gradient centrifugation indicate that kinase I has a molecular weight of about 9.5 - 10(5) (25 S) and kinase II about 1.4 - 10(6) (32 S). These enzymes can utilize either ATP or GTP as the phosphoryl donor. Among various protein substrates examined, these kinases catalyze the phosphorylation of casein greater than 50% dephosphorylated phosvitin congruent to 50% dephosphorylated casein greater than phosvitin. Histones, protamine and bovine serum albumin are poor phosphoryl acceptors. Kinetic data indicate that both enzymes are inhibited by high casein substrate concentrations which may be partially relieved by NaCl. Both phosphotransferases require Mg(2+) for activity and are optimally active at pH 9.0. The enzymes have apparent Km values of 2.5 - 10(-5) M for GTP, 2 - 10(-5) M for ATP, and 0.4--0.6 mg/ml for casein. The incorporation of the terminal phosphate of GTP into casein as catalyzed by these enzymes is inhibited to varying degrees by ATP, ITP, ADP, and GDP but not by UTP, CTP, GMP, adenosine 3':5'-cyclic monophosphate, and guanosine 3':5'-cyclic monophosphate. In addition, NaF and 2,3-diphosphoglyceric acid are also found to inhibit the activity of both kinases. The effect of 2,3-diphosphoglycerate is interesting and suggests that this metabolite may regulate the activity of the casein kinases in the red blood cells.
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PMID:Multiple forms of casein kinase from rabbit erythrocytes. 0 76

Purine nucleotide pyrophosphotransferase was purified to apparent homogeneity from a culture filtrate of Streptomyces morookaensis. It is a monomeric protein with a molecular weight of 24 000-25 000, and its isoelectric point is 6.9. The enzyme synthesizes purine nucleoside 5'-phosphate (mono, di, or tri) 3'-diphosphates such as pppApp, ppApp, pApp, pppGpp, ppGpp and pppIpp by transferring a pyrophosphoryl group from the 5'-position of ATP, dATP and ppApp to the 3'-position of purine nucleotides. The purified enzyme catalysed the formation of 435 mumol of pppApp and 620 mumol of pppGpp from ATP and GTP per min mg protein under the standard conditions. The enzyme requires absolutely a divalent cation for activity, and optimum pH for the enzyme activity lay above 10 for Mg2+, for Co2+ and Zn2+ from 9 to 9.5, and for Fe2+ from 7.5 to 8. The following Michaelis constants were determined: AMP, 2.78 mM; ADP, 3.23 mM; GMP, 0.89 mM; GDP, 0.46 mM and GTP, 1.54 mM, in the case of ATP donor. The enzyme is inhibited by guanine, guanosine, dGDP, dGTP, N-bromosuccinimide, iodacetate, sodium borate and mercuric acetate.
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PMID:Purine nucleotide pyrophosphotransferase from Streptomyces morookaensis, capable of synthesizing pppApp and pppGpp. 0 Oct 88

Citrate synthase activity of Saccharomyces cerevisiae was determined by a radioactive assay procedure and the reaction product, 14C-citric acid, was identified by chromatographic techniques. ATP, d-ATP, GTP and NADH were most inhibitory to the citrate synthase invitro. The activity was inhibited to a lesser extent by ADP, UTP, and NADP whereas, AMP and CTP were much less inhibitory. NADH, like NAD, glutamic acid, glutamine, arginine, ornithine, proline, aspartic acid and alpha-ketoglutarate exhibited no inhibition. These results have been discussed in the light of the role of citrate synthase for the energy metabolism and glutamic acid biosynthesis.
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PMID:Regulation of citrate synthase activity of Saccharomyces cerevisiae. 0

1. Renal tubular membranes from rat kidneys were prepared, and adenylate cyclase activity was measured under basal conditions, after stimulation by NaF or salmon calcitonin. Apparent Km value of the enzyme for hormone-linked receptor was close to 1 x 10(-8) M. 2. The system was sensitive to temperature and pH. pH was found to act both on affinity for salmon calcitonin-linked receptor and maximum stimulation, suggesting an effect of pH on hormone-receptor binding and on a subsequent step. 3. KCl was without effect areas whereas CoCl and CaCl2 above 100 muM and MnCl2 above 1 muM inhibited F- -and salmon calcitonin-sensitive adenylate cyclase activities. The Ca2+ inhibition of the response reflected a fall in maximum stimulation and not a loss of affinity of salmon calcitonin-linked receptor for the enzyme. 4. The measurement of salmon calcitonin-sensitive adenylate cyclase activity as a function of ATP concentration showed that the hormone increases the maximum velocity of the adenylate cyclase. GTP, ITP and XTP at 200 muM did not modify basal, salmon calcitonin- and parathyroid hormone-sensitive adenylate cyclase activities. 5. Basal, salmon calcitonin- and F- -sensitive adenylate cyclase activities decreased at Mg2+ concentrations below 10 mM. High concentrations of Mg2+ (100 mM) led to an inhibition of the F- -stimulated enzyme. 6. Salmon calcitonin-linked receptor had a greater affinity for adenylate cyclase than human or porcine calcitonin-linked receptors. There was no additive effect of these three calcitonin peptides whereas parathyroid hormone added to salmon calcitonin increased adenylate cyclase activity, thus showing that both hormones bound to different membrane receptors. Human calcitonin fragments had no effect on adenylate cyclase activity. 7. Salmon calcitonin-stimulated adenylate cyclase activity decreased with the preincubation time. This was due to progressive degradation of the hormone and not to the rate of binding to membrane receptors.
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PMID:Calcitonin-sensitive adenylate cyclase in rat renal tubular membranes. 0 53

A new, very sensitive, rapid and reliable assay for guanylate cyclase has been established based on conversion of [32P]GTP to [32P]guanosine 3':5'-monophosphate and its separation on Dowex 50 and aluminium oxide columns. The optimum conditions for the assay of mouse parotid guanylate cyclase have been established and using this procedure the properties of the enzyme have been investigated. The enzyme was found in both the particulate and supernatant fractions. The particulate enzyme was activated 12-fold by Triton X-100 and the supernatant enzyme activity increased 2-fold. In the presence of detergent guanylate cyclase activity was distributed 85% in the particulate and 15% in the supernatant fractions, respectively. The particulate activity was localised in a plasma membrane fraction. Guanylate cyclase activity was also assayed in a wide variety of other tissues. In all cases enzymatic activity was found in both the particulate and supernatant fractions. The distribution varied with the tissue but only the intestinal mucosa had a greater proportion of total guanylate cyclase activity in the particulate fraction than the parotid. The two enzymes showed some similar properties. Their pH optima were pH 7.4, both enzymes were inhibited by ATP, dATP, dGTP and ITP, required Mn2+ for activity and plots of activity versus Mn2+ concentration were sigmoidal. However, in many properties the enzymes were dissimilar. The ratios of Mn2+ to GTP for optimum activity were 4 and 1.5 for the supernatant and plasma-bound enzymes, respectively. The slope of Hill plots for the supernatant enzyme with varying Mn2+ was 2. The particulate enzyme plots also had a slope of 2 at low Mn2+ concentration but at higher concentrations (above 0.7 mM) the Hill coefficient shifted abruptly to 4. Calcium ions reduced sigmoidicity of the kinetics lowering the Hill coefficient, activated the enzyme at all Mn2+ concentrations but had no effect on the Mn2+:GTP ratio with the supernatant enzyme while with the plasma membrane enzyme Ca2+ had no effect on the sigmoid form of the kinetics at low Mn2+ but prevented the shift to a greater Hill coefficient at higher Mn2+, inhibited the activity at low Mn2+ and shifted the Mn2+:GTP optimum ratio to 4. For the particulate enzyme plots of activity versus GTP concentration were sigmoid (n = 1.3), while the supernatant enzyme exhibited hyperbolic kinetics.
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PMID:Guanylate cyclase: assay and properties of the particulate and supernatant enzymes in mouse parotid. 0 69

Structural requirements for substrate binding to histidyl-tRNA synthetase from Salmonella typhimurium have been investigated using ATP analogues. Ki values and the relative binding affinity of the enzyme for these analogues have been determined in the tRNA aminoacylation reaction. The enzyme is highly specific for ATP: no binding was found for GTP, CTP, TTP and UTP. dATP is a very poor substrate for acylation of tRNA, with a Km 40-fold higher than that of ATP. Binding of adenosine 5'-triphosphate requires interactions of the amino group of adenosine and the sugar moiety; the 2' and the 5' positions of the ribose appear to be essential for recognition; the phosphate groups enhance the binding. AMP is a noncompetitive inhibitor with ATP. The interaction of histidyl-tRNA synthetase, a dimeric enzyme, with histidine and ATP was examined by fluorescence measurements at equilibrium and by equilibrium dialysis. Binding with L-histidine is significantly tighter at pH 6 than at pH 7, while the ATP binding is independent of pH. The stoichiometry was measured at pH 6 than at pH 7, while the ATP binding is independent of pH. The stoichiometry was measured at pH 7.5 by equilibrium dialysis and is 1 mol ATP/mol enzyme and, variably, close to 2 or 1 mol histidine/mol enzyme.
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PMID:Histidyl transfer ribonucleic acid synthetase from Salmonella typhimurium. Interaction with substrates and ATP analogues. 0 14

The general aim was to define some of the most important parameters involved in the coupling step between the synthetic analog of adrenocoricotropin hormone (beta1-24-corticotropin tetracosa peptide) and the catalytic unit of the adenylate-cyclase system of fat cells. These studies were performed with a purified plasma membrane fraction from rat adipose tissue. In this regard, some effects of ions, pH, and nucleotides (ATP nad GTP) on this hormone sensitive system were studied A simple model based on a random association process of reactants yeilded a statisfactory approximation of the kinetic data. In contract to results obtained by two other groups, which were analyzed by De Haen, no evidence was found for a regulation of the adenylate-cyclase activity by the adenosine triphosphate which was not complexed to magnesium...
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PMID:[The coupling of beta1-24-corticotropin to the adenylate-cylase system in rat adipocytes. Evidence for hormone-nucleotides interaction (author's transl)]. 0 15

The autophosphorylation of rabbit and human erythrocyte membranes has been studied under various experimental conditions. The phosphopeptides of the erythocyte membranes were identified using sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis followed by ratioautography. The pattern of phosphorylatiion of membrane components differs with respect to the phosphoryl donor used (ATP or GTP) and to the pH at which the reaction is carried out. Both species appear to contain at least two distinct membrane-bound protein kinases. The human erythrocyte membrane contains a cyclic adenosine 3'5'-monophosphate (cyclic AMP)-dependent protein kinase and several substrates for this kinase. Only ATP can be used as a phosphoryl donor for this kinase. In contrast, the rabbit erythrocyte membrane does not contain a cyclic AMP dependent protein kinase but does contain a kinase which utilizes only ATP as the phosphoryl donor and is specific for certain endogenous substrates at low pH. Both the human and rabbit erythrocyte membranes contain a kinase which utilizes GTP, perhaps also ATP, as the phosphoryl donor. The substrates of these kinases are similar in both species.
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PMID:An analysis of the autophosphorylation of rabbit and human erythrocyte membranes. 0 93

1. Four fractions of protein kinase (EC 2.7.1.37) activity (Peak IH, IIH, IIIC and IVC) have been resolved and partially purified from the 100 000 X g supernatant fraction of bovine parotid glands by DEAE-cellulose and phosphocellulose chromatographies. 2. The protein kinases of Peak IH and IIH were adenosine 3',5'-monophosphate (cyclic AMP) -dependent and had similar enzymic properties. The enzyme activities of Peak IIIC and IVC were cyclic-AMP independent, but there were some distinct differences between their properties. The protein kinase in Peak IIIC was activated by 0.2 M NaCl or KCl and phosphorylated casein preferentially as the substrate, utilizing only ATP as a phosphate donor. On the other hand, the protein kinase in Peak IVC was inhibited by univalent salts and preferred phosvitin to casein, utilizing either ATP or GTP as a phosphate donor. 3. Tolbutamide increased the Km value for ATP and the dissociation constant for cyclic AMP, resulting in the inhibition of cyclic-AMP dependent protein kinase activity in the presence of cyclic AMP. Tolbtamide and its carboxy derivative, 1-butyl-3-p-carboxyphenylsulfonylurea, exerted almost no inhibitory effect on either the cyclic-AMP dependent protein kinase activities in the absence of cyclic AMP or on the cyclic-AMP independent protein kinase activities.
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PMID:Characterization of protein kinases from bovine parotid glands. The effect of tolbutamide and its derivative on these partially purified enzymes. 0 16

The dependence of the rate of dephosphorylation of ATP, ITP, GTP and CTP (= NTP), expressed as first-order rate constants (50 degrees C; I = 0.1 M, NaClO4), on pH (2 to 10), in the absence and presence of Mn2+, Ni2+, and Zn2+, was investigated. The reaction is accelerated by Zn2+ and passes through a pH optimum at about 8 for the system Zn2+-ATP or 9 for Zn2+-ITP and Zn2+-GTP; this is analogous to observations made earlier with the corresponding Cu2+ systems. By computing the pH dependence of the distribution of the several species present in these systems it is shown that the highest rates are observed in the pH regions where the concentration of Zn(ATP)2-, Zn(ITP-H)3-, or Zn(GTP-H)3- dominates. By evaluating the pH dependence evidence is given that the attacking nucleophile is OH- or H2O for Zn (ATP)2- and H2O for Zn (ITP-H)3- or Zn(GTP-H)3-. For all these complexes metal-ion/nucleic-base interactions are known, leading to the formation of macrochelates. These metal-ion/nucleic-base interactions are crucial for the observation of a metal-ion-promoted dephosphorylation; in agreement with this, and the small tendency of the cytosine moiety to coordinate, the CTP systems are rather stable towards dephosphorylation. It should be noted that these experimental results do not necessarily mean that the macrochelates usually described are the reactive complexes, but only that the active complex must be closely related to them (e.g. isomers, etc). Although for the Ni2+ systems with ATP, ITP, and GTP, and for the Mn2+-ATP system a metal-ion/nucleic-base interaction is also known, these systems are not very sensitive to hydrolytic cleavage of the terminal P-O-P bond. The only known significant structural difference between the Ni2+-NTP or the Mn2+-ATP complexes and those of Cu2+ or Zn2+ is that Ni2+ Mn2+ coordinate to all three phsophate groups, whereas Cu2+ and Zn2+ involve only the beta and gamma ones. This structure-reactivity relationship is rationalized by the suggestion that in the active species the metal ion should be coordinated to the alpha,beta-phosphate groups leaving the gamma-group open to nucleophilic attack. Obviously, an initial beta,gamma-coordination is suitable for a shift of the metal ion along the phosphate back-bone into the reactive alpha-beta-position, while for an alpha,beta,gamma-coordination only the less favorable removal of the coordinated gamma-group remains. The metal-ion/nucleic-base interaction is considered as being important for achieving this reactive structure. The connection between trans-phosphorylation in vitro and in vivo is discussed. It is also shown that the formation of mixed-ligand or ternary complexes inhibits the dephosphorylation process. This is on the one hand of interest with regard to the transport of hydrolysis-sensitive phosphates in nature, while on the other it casts doubts on conclusions based on experiments carried out in the presence of buffers, because these contain weak bases and hence potential ligands.
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PMID:Comparison of the metal-ion-promoted dephosphorylation of the 5'-triphosphates of adenosine, inosine, guanosine and cytidine by Mn2+, Ni2+ and Zn2+ in binary and ternary complexes. 0 27


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