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

---

Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A membrane fraction enriched in parathyroid hormone (PTH)-sensitive adenylate cyclase and sodium and potassium ion-activated (Na+, K+)-ATPase was prepared from bovine kidney. Tritiated PTH binding to this membrane fraction was dependent on both hormone and membrane protein concentration. Both total and specific binding of the hormone decreased significantly after 5 to 10 min of incubation at 22 degrees. PTH binding was highly specific, being sensitive to inhibition only with active forms of unlabeled hormone (native and 1-34 PTH). Specific binding showed a pH optimum of 7.3 to 7.5. Inhibition of binding of tritiated hormone by unlabeled PTH was also highly effective at pH 6.0, but this apparently specific binding was also inhibited by adrenocorticotropic hormone, insulin, glucagon, and vasopressin. Dissociation of bound hormone was demonstrated, and an apparent dissociation constant of 4.6 X 10(-2) min-1 was obtained. Specific binding was eliminated by pretreatment of the membranes with trypsin. The concentration dependence for inhibition of binding with unlabeled PTH was identical to that for activation of adenylate cyclase in this membrane preparation, and binding was also inhibited by concentrations of calcium in the 0.5 to 2 mM range.
...
PMID:Binding of tritiated bovine parathyroid hormone to plasma membranes from bovine kidney cortex. 1 29

(1) The mitochondrial ATPase (EC 3.6.1.3) Ehrlich ascites cell mitochondria, was inhibited by D-glucose under physiological concentrations of ATP. The generation of ADP by the mitochondrial bound hexokinase, seems to be the reason for the D-glucose inhibitory effect. Reversal of the inhibitory effect of ADP on Ehrlich ascites cell mitochondria ATPase by an ATP-regenerating system was achieved. (2) Dissociation of mitochondrial bound hexokinase from the mitochondria eliminated the inhibitory effect of D-glucose. Rebinding of the hexokinase to the mitochondria regenerated the D-glucose inhibitory effect on Ehrlich ascites cell mitochondria ATPase. (3) Bioflavonoids such as quercetin inhibit the mitochondrial hexokinase activity, but do not change the mitochondrial ATPase activity of isolated Ehrlich ascites tumor cell mitochondria. (4) The inhibitory effect of bioflavonoids on mitochondrial bound hexokinase activity is shown to be dissociable from the ascites tumor cell mitochondria and seems to be associated with regulatory rather than catalitic sites of the enzyme.
...
PMID:Bioflavonoid regulation of ATPase and hexokinase activity in Ehrlich ascites cell mitochondria. 1 95

Ouabain binding capacity of cell membranes is directly related to (Na+ + K+)-ATPase activity. The extent of ouabain inhibition of (Na+ + K+)-ATPase is a measure of ouabain receptor sites occupied. Dissociation constants of the ouabain-receptor complexes are identical in all organs in a single species but vary among different species. K+ decreases the association rate constant of the ouabain receptor interaction without altering the dissociation rate constants. Titration of digoxin-inhibited (Na+ + K+)-ATPase from guinea pig heart with digoxin antibodies shows a reversal of the inhibition at lower antibody concentrations in the presence of K+ than in the absence of K+. It is concluded that digitalis intolerance in acute hypokalemia reflects the increased affinity of the cardiac glycoside receptor under these conditions.
...
PMID:Cardiac glycoside receptor in potassium depletion. 12 57

Dissociation of the (Na+ + K+)-ATPase ouabain complex, formed in the presence of Mg2+ and inorganic phosphate (Complex II), is inhibited by Mg2+ (21-45%) and the alkali cations Na+ (25-59%) and K+ (27-75%) when kidney cortex tissue (bovine, rabbit, guinea pig) is the enzyme source. Choline chloride at 200 mM, equivalent to the highest concentration of NaCl tested, does not inhibit. Dissociation of Complex II from brain cortex (bovine, rat, rabbit) or heart muscle (rabbit) is much less inhibited: 0-11% by Na+ and 11-19% by K+. The degree of inhibition is not directly related to the size of the dissociation rate constant (k-) of the various complexes, but rather to the extent of interaction between the cation and ouabain binding sites for these tissues. Inhibition curves for Na+ and K+ are sigmoidal. Half-maximal inhibition for rabbit brain and kidney cortex is at 30-40 mM Na+ and 6-10 mM K+, and the maximally inhibitory concentrations are 50-150 and 15-20 mM, respectively. Maximal inhibition by Na+ or K+ for these tissues is the same. For guinea pig kidney cortex Na+ and K+ are almost equally effective, but 150 mM K+ or 200 mM Na+ are still not saturating, and inhibition curves indicate high- and low-affinity binding sites for the alkali cations. The inhibition curve for Mg2+ is not sigmoidal. In the kidney preparations Mg2+ inhibits half-maximally at 0.4-0.5 mM, maximally at 1-3 mM. Maximal inhibition by Mg2+ is higher than by Na+ or K+ for rabbit kidney cortex and lower for guinea pig kidney cortex. There is no competition or additivity among the cations, indicating the existence of different binding sites for Mg2+ and the alkali cations. Complex II differs in stability in the extent of inhibition, in the dependence of inhibition on the cation concentration and in the absence of antagonism between Na+ and K+, from the ouabain complex formed via phosphorylation by ATP (Complex I). This indicates that the phosphorylation states for the complexes are clearly different.
...
PMID:Studies on (Na+ plus K+)-activated ATPase. XXXVII. Stabilization by cations of the enzyme-ouabain complex formed with Mg1+ and inorganic phosphate. 12 79

Anthroylouabain (AO) was synthesized by reaction of anthracene-9-carboxylic chloride with ouabain. Nuclear magnetic resonance spectroscopy of AO suggests that the anthracene is esterfied to the rhamnose in the glycoside. AO inhibits Na-K ATPase from human red cells, eel electroplax and rabbit and dog kidney with a KI less than 1muM. AO bound to rabbit or dog kidney Na-K ATPase shows enhanced fluorescence and characteristic spectral shifts. AO binding requires Mg and is optimum in the presence of Mg + Pi or MgATP + Na; ouabain prevents AO binding and fluorescence enhancement if added before AO or reverses it if added after AO is bound. Na inhibits AO binding in the presence of Mg + Pi and K inhibits it in the presence of MgATP + Na. AO binding and dissociation rate constants measured by fluorescence agree qualitatively with reported measurements for ouabain, using other methods, although AO shows faster kinetics than ouabain. Dissociation constants obtained from kinetic measurements are 1.5 X 10(-7) and 1.8 X 10(-7) M for the MgATP + Na complex and Mg + Pi complex, respectively. KD from fluorescence titrations is 2.3 X 10(-7) M for the latter. The enzyme has 2-2.5 nmol of AO binding sites/mg of protein. No differences in the fluorescence parameters of the Mg + Pi or MgATP + Na complexes were observed, suggesting that the same enzyme conformation binds AO under both ligand conditions. Comparison of the AO fluorescence parameters in the enzyme with those of model systems suggests that the binding site is hydrophobic and/or viscous and shielded from H2O. The results indicate that AO is a specific fluorescent probe of the cardiac glycoside receptor of the Na-K ATPase. Possible applications are discussed.
...
PMID:Anthroylouabain: a specific fluorescent probe for the cardiac glycoside receptor of the Na-K ATPase. 13 37

The association and dissociation rate constants for the interaction of [3H]-ouabain with partially purified rat brain (Na+,K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) in vitro were estimated from the time course of the [3H]-ouabain binding observed in the presence of Na+, Mg2+ and ATP by a polynomial approximation-curve-fitting technique. The reduction of the association rate constant by K+ was greater than its reduction of the dissociation rate constant. Thus, the affinity of Na+,K+)-ATPase for ouabain was reduced by K+. The binding-site concentration was unaffected by K+. Consistent with these findings, the addition of KCl to an incubation mixture at the time when [3H]-ouabain binding to (Na+,K+)ATPase is close to equilibrium, caused an immediate decrease in bound ouabain concentration, apparently shifting towards a new, lower equilibrium concentration. Dissociation rate constants which were estimated following the termination of the ouabain-binding reaction were different from those estimated with above methods and may not be useful in predicting the ligand effects on equilibrium of the ouabain-enzyme interaction.
...
PMID:Kinetics studies on the interaction between ouabain and (Na+,K+)-ATPase. 13 32

1. The naturally occurring ATPase (adenosine triphosphatase)-inhibitor protein, from bovine heart mitochondria, was obtained as a single pure protein. It was not identical with any of the five subunits (alpha-epsilon) of the isolated ATPase, and appeared to be a single polypeptide chain. 2. The inhibitor combined with the ATPase in a 1:1 molar ratio, producing a completely inhibited ATPase molecule. The affinity of the ATPase for its inhibitor is high; the K(d) is of the order of 10(-8)m. 3. The enthalpy of the ATPase-inhibitor complex-formation is positive, the value of K(d) decreasing as the temperature is raised. This suggests that the forces involved are largely hydrophobic in nature. 4. Hydrolysis of a nucleoside triphosphate promoted formation of the ATPase-inhibitor complex, although the equilibrium position was almost unaffected by the rate of hydrolysis. At low salt concentration, less than 200 turnovers of the ATPase suffice for the ATPase to combine with the inhibitor protein. At higher salt concentrations, a larger number of turnovers is required. It is suggested that the inhibitor binds to a form of the ATPase that is produced transiently during hydrolysis. 5. In the presence of 75mm-K(2)SO(4), the rates of association and dissociation are slow enough to allow their kinetics to be studied. Association is first-order in inhibitor concentration, but fractional order in ATPase concentration. Dissociation is first-order in ATPase-inhibitor complex concentration. The temperature coefficients of the ;on' and ;off' processes were also measured. 6. A simple kinetic model for the ATPase-inhibitor interaction is proposed that can be extended to take into account release of inhibitor protein under energized conditions on the membrane. 7. The isolated ATPase is inhibited by preincubation with Mg(2+), reversible by subsequent addition of EDTA, and by ADP, reversible by subsequent addition of ATP. These effects are not found on the membrane-bound ATPase. The mechanism of these effects is discussed.
...
PMID:A thermodynamic analysis of the interaction between the mitochondrial coupling adenosine triphosphatase and its naturally occurring inhibitor protein. 15 88

1. Isolation of ATPase from rat liver submitochondrial particles by chloroform treatment requires the presence of ATP or ADP during enzyme solubilization. In the absence of adenine nucleotides the enzyme activity is very low although all protein components of F1-ATPase are released. The low concentrations of ATP or ADP required (5 microM) indicate that the high affinity nucleotide-binding sites are involved in enzyme stabilization. Other nucleotides tested (ITP, GTP, UTP, CTP) were found to be less effective. 2. Polyacrylamide gel electrophoresis and immunodiffusion in agar plates revealed that in the absence of adenine nucleotides a fraction of F1-ATPase released by chloroform treatment is split into fragments. The part of the dissociated enzyme molecule has a molecular weight identical with that of a beta-subunit of F1-ATPase. 3. Dissociation of the F1-ATPase molecule could also be prevented by aurovertin. 4. Crude F1-ATPase solubilized by chloroform treatment can be further purified by Sepharose 6B gel filtration. Specific ATPase activity of the purified enzyme was 90 mumol Pi/min per mg protein and the enzyme was composed of five protein subunits (alpha, beta, gamma, delta, epsilon) with molecular weights 58 000, 55 000, 28 000, 13 000 and 8000, respectively. 5. Chloroform-released F1-ATPase from rat liver mitochondria displayed immunochemical cross-reactivity with that isolated from beef heart mitochondria.
...
PMID:Stabilization of rat liver mitochondrial F1-adenosine triphosphatase during chloroform-induced solubilization. 15 60

EPR and water proton relaxation rate (1/T1) studies of partially (40%) and "fully" (90%) purified preparations of membrane-bound (Na+ + K+) activated ATPase from sheep kidney indicate one tight binding site for Mn2+ per enzyme dimer, with a dissociation constant (KD = 0.88 muM) in agreement with the kinetically determined activator constant, identifying this Mn2+-binding site as the active site of the ATPase. Competition studies indicate that Mg2+ binds at this site with a dissociation constant of 1 mM in agreement with its activator constant. Inorganic phosphate and methylphosphonate bind to the enzyme-Mn2+ complex with similar high affinities and decrease 1/T1 of water protons due to a decrease from four to three in the number of rapidly exchanging water protons in the coordination sphere of enzyme-bound Mn2+. The relative effectiveness of Na+ and K+ in facilitating ternary complex formation with HPO2-4 and CH3PO2-3 as a function of pH indicates that Na+ induces the phosphate monoanion to interact with enzyme-bound Mn2+. Thus protonation of an enzyme-bound phosphoryl group would convert a K+-binding site to a Na+-binding site. Dissociation constants for K+ and Na+, estimated from NMR titrations, agreed with kinetically determined activator constants of these ions consistent with binding to the active site. Parallel 32Pi-binding studies show negligible formation (less than 7%) of a covalent E-P complex under these conditions, indicating that the NMR method has detected an additional noncovalent intermediate in ion transport. Ouabain, which increases the extent of phosphorylation of the enzyme to 24% at pH 7.8 and to 106% at pH 6.1, produced further decreases in 1/T1 of water protons. Preliminary 31P- relaxation studies of CH3PO2-3 in the presence of ATPase and Mn2+ yield an Mn to P distance (6.9 +/- 0.5 A) suggesting a second sphere enzyme-Mn-ligand-CH3PO2-3 complex. Previous kinetic studies have shown that T1+ substitutes for K+ in the activation of the enzyme but competes with Na+ at higher levels. From the paramagnetic effect of Mn2+ at the active site on the enzyme on I/T1 of 205T1 bound at the Na+ site, a Mn2+ to T1+ distance of 4.0 +/- 0.1 A is calculated, suggesting the sharing of a common ligand atomy by Mn2+ and T1+ on the ATPase. Addition of Pi increases this distance to 5.4 A consistent with the insertion of P between Mn2+ and T1+. These results are consistent with a mechanism for the (Na+ + K+)-ATPase and for ion transport in which the ionization state of Pi at a single enzyme active site controls the binding and transport of Na+ and K+, and indicate that the transport site for monovalent cations is very near the catalytic site of the ATPase. Our mechanism also accounts for the order of magnitude weaker binding of Na+ compared to K+.
...
PMID:Magnetic resonance and kinetic studies of the mechanism of membrane-bound sodium and potassium ion- activated adenosine triphosphatase. 17 21

Activation of membrane-associated thiamin triphosphatase from rat brain requires a divalent cation (Mg2+, Ca2+, or Mn2+). The optimum concentration of Mg2+ necessary for maximal enzyme activity varies with substrate concentration; conversely, the maximal rate of hydrolysis attainbale by increasing thiamin triphosphate concentration is directly proportional to [Mg2+] for all levels of Mg2+ below that of the substrate. Under appropriate conditions, the Km of the thiamin triphosphatase for Mg2+ and for thiamin triphosphate are shown to be identical. Dissociation constants (Kd) for the binding of Mg2+ to thiamin triphosphate, thiamin diphosphate, and thiamin were determined; kinetic data re-expressed in terms of [Mg2+-thiamin triphosphate] conform to simple single substrate predictions, suggesting that the true enzyme substrate may be the Mg2+-thiamin triphosphate complex. Excess free Mg2+ inhibits thiamin triphosphatase activity competitively while excess free thiamin triphosphate in concentrations up to 10 times Km has no effect on the membrane-bound enzyme.
...
PMID:Membrane-associated thiamin triphosphatase. II. Activation by divalent cations. 17 10


1 2 3 4 5 6 7 Next >>

---