Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Membrane vesicles from Azotobacter vinelandii O prepared by osmotic lysis of spheroplasts in tris (hydroxymethyl) aminomethane/acetate buffer (pH 7.8) contain a latent adenosine triphosphatase (ATPase). The ATPase can be activated when the vesicles are incubated in the presence of an electron donor (D-lactate) and a mixture of adenosine diphosphate and inorganic phosphate or by controlled treatment with trypsin. After the ATPase is activated, the membrane vesicles in the presence of adenosine triphosphate accumulate calcium but not glucose or rubidium (in the presence of valinomycin). ATP-dependent calcium uptake follows Michaelis-Menten kinetics with a Km of 48 muM and a Vmax of 20 nmol/min/mg of membrane protein and is highly specific for calcium over cations magnesium, barium, lanthanum, sodium, potassium, and lithium. The calcium accumulated in the presence of ATP is freely exchangeable with external calcium and is rapidly released in the presenceof uncouplers or ATPase inhibitors. Calcium uptake in the presenceof ATP is blocked by dicyclohexylcarbodiimide, ADP, p-chloromercuriphenylsulfonate, by the proton-conducting ionophores m-chlorophenylcarbonylcyanide hydrazone, nigericin, monensin, and gramicidin D, but not by potassium cyanide, anoxia, or valinomycin (in the presence of potassium). Measurements of the external pH of vesicle suspensions reveal that protons are actively taken up by the membranes during hydrolysis of ATP. These results suggest that vesicles prepared under these conditions have a topology which is inverted with respect to the intact cell and that calcium is accumulated by means of proton antiport.
 ...
PMID:ATP-dependent calcium transport in isolated membrane vesicles from Azotobacter vinelandii. 0 92

Mutations at the OLI 1 or OLI 2 loci of mitochondria DNA in Saccharomyces cerevisiae are associated with a diminished growth rate in nutritionally suboptimal cultures supplemented with an oxidizable carbon source. In the case of mutant OR146(OLI1) there is a 35% loss of mitochondrial protein during fractionation in vitro, suggesting that the mutationally altered adenosine triphosphatase(ATPase) confers some instability on the mitochondrial membrane. The possibility is discussed that this reflects an unstable mitchondrial population in vivo, leading the observed growth deficiency. Mitochondria from mutant OR146 at the OLI 1 locus show a relatively oligomycin-resistant State-3 respiration, but the same ADP/O and respiratory-control quotients as the isonuclear wild-type. A slightly lowered Qo2 with NADH-linked substrates was observed and is discussed. For both strains the apparent H+/O ratios were close to 4 with pyruvate, ethanol and alpha-oxoglutarate, but consistently lower with succinate and citrate. For each substrate a characteristic t 1/2 (time for half-decay of the transmembrane pH differential) range was found, consistent with the view that the substrates effecitvely carry the protons back across the membrane. As expected, H+/O ratios were independent of t 1/2 for all substrates, with the exception of alpha-oxoglutarate in the case of the wild-type, where an inverse correlation was found. The lack of this correlation in the case of the mutant was the only apparent difference in the translocation parameters observed. A hypothesis relating this to the functioning of the oligomycin-resistant ATPase is proposed.
 ...
PMID:An oligomycin-resistant adenosine triphosphatase and its effects on cellular growth, mitochondrial oxidative phosphorylation and respiratory proton translocation in Saccharomyces cerevisiae. 1 56

Chromaffin granules isolated from bovine adrenal gland were incubated with (3)H-labelled nucleotides and [(14)C]noradrenaline to study the uptake of these substances. [(3)H]ATP, [(3)H]ADP and [(3)H]AMP are taken up by these organelles by the same temperature-dependent mechanism. The apparent K(m) for ATP and ADP is 1.4mm, and for AMP it is 2.9mm. The uptake of ATP has a flat pH optimum, whereas the catecholamine uptake increases with more alkaline pH. Atractyloside and carboxyatractyloside are competitive and specific inhibitors of nucleotide uptake, whereas reserpine inhibits only that for catecholamines. Mg(2+) ions activate uptake of both catecholamine and nucleotides, whereas EDTA and N-ethylmaleimide inhibit these processes. Nucleotide and catecholamine uptakes are inhibited by uncouplers of oxidative phosphorylation and by two ATP analogues. NH(4) (+) ions and nigericin in the presence of KCl inhibit only catecholamine uptake. It is concluded that nucleotide uptake, as proposed previously for catecholamine uptake, depends on an electrochemical proton gradient produced by a proton-translocating adenosine triphosphatase localized in the membrane of chromaffin granules. Furthermore, as suggested by the effect of NH(4) (+) and nigericin, catecholamine uptake apparently depends on the chemical part of this gradient, whereas the results for nucleotide uptake are consistent with its dependence on the electrical component.
 ...
PMID:A characterization of the nucleotide uptake of chromaffin granules of bovine adrenal medulla. 2 25

Basal and trypsin-stimulated adenosine triphosphatase activities of Escherichia coli K 12 have been characterized at pH 7.5 in the membrane-bound state and in a soluble form of the enzyme. The saturation curve for Mg2+/ATP = 1/2 was hyperbolic with the membrane-bound enzyme and sigmoidal with the soluble enzyme. Trypsin did not modify the shape of the curves. The kinetic parameters were for the membrane-bound ATPase: apparent Km = 2.5 mM, Vmax (minus trypsin) = 1.6 mumol-min-1-mg protein-1, Vmax (plus trypsin) = 2.44 mumol-min-1-mg protein-1; for the soluble ATPase: [S0.5] = 1.2 mM, Vmax (-trypsin) = 4 mumol-min-1-mg protein-1; Vmax (+ trypsin) = 6.6 mumol-min-1-mg protein-1. Hill plot analysis showed a single slope for the membrane-bound ATPase (n = 0.92) but two slopes were obtained for the soluble enzyme (n = 0.98 and 1.87). It may suggest the existence of an initial positive cooperativity at low substrate concentrations followed by a lack of cooperativity at high ATP concentrations. Excess of free ATP and Mg2+ inhibited the ATPase but excess of Mg/ATP (1/2) did not. Saturation for ATP at constant Mg2+ concentration (4 mM) showed two sites (groups) with different Kms: at low ATP the values were 0.38 and 1.4 mM for the membrane-bound and soluble enzyme; at high ATP concentrations they were 17 and 20 mM, respectively. Mg2+ saturation at constant ATP (8 mM) revealed michealian kinetics for the membrane-bound ATPase and sigmoid one for the protein in soluble state. When the ATPase was assayed in presence of trypsin we obtained higher Km values for Mg2+. These results might suggest that trypsin stimulates E. coli ATPase by acting on some site(s) involved in Mg2+ binding. Adenosine diphosphate and inorganic phosphate (Pi) act as competitive inhibitors of Escherichia coli ATPase. The Ki values for Pi were 1.6 +/- 0.1 mM for the membrane-bound ATPase and 1.3 +/- 0.1 mM for the enzyme in soluble form, the Ki values for ADP being 1.7 mM and 0.75 mM for the membrane-bound and soluble ATPase, respectively. Hill plots of the activity of the soluble enzyme in presence of ADP showed that ADP decreased the interaction coefficient at ATP concentrations below its Km value. Trypsin did not modify the mechanism of inhibition or the inhibition constants. Dicyclohexylcarbodiimide (0.4 mM) inhibited the membrane-bound enzyme by 60-70% but concentrations 100 times higher did not affect the residual activity nor the soluble ATPase. This inhibition was independent of trypsin. Sodium azide (20 muM) inhibited both states of E. coli ATPase by 50%. Concentrations 25-fold higher were required for complete inhibition. Ouabain, atebrin and oligomycin did not affect the bacterial ATPase.
 ...
PMID:Membrane bound and soluble adenosine triphosphatase of Escherichia coli K 12. Kinetic properties of the basal and trypsin-stimulated activities. 12 30

The properties of a Ca2+ activated adenosine triphosphatase shown to be present in homogenates of purified rat peritoneal mast cells were investigated. The enzyme was activated by Ca2+, Mg2+, and to a lesser extent by Mn2+ and Co2+. Ca2+ alone was necessary for full activity and the further addition of Mg2+ did not have any effect. The chelating agents EGTA (ethanedioxybis(ethylamine)tetra-acetate) and EDTA completely inhibited the reaction. The pH optimum was 7.8. Reduced glutathione, cysteine, dithiothreitol, N-ethylmaleimide, urea, ADP, NaF, increasing ionic strength and Triton X-100 all inhibited the reaction. On subcellular fractionation of mast-cell homogenates by density-gradient centrifugation, the distribution of Ca2+ activated adenosine triphosphatase resembled that of 5'-nucleotidase, but differed from that of the other markers used, suggesting localization in the plasma membrane. Further experiments indicated that the enzyme is present on the external surface of the plasma membrane.
 ...
PMID:Characterization of calcium-ion-activated adenosine triphosphatase in the plasma membrane of rat mast cells. 13 82

The cytochemical localization and intensity of adenosine triphosphatase (ATPase) activity in the spermatozoa from fertile and infertile human ejaculate were observed by an electron microscope. Sperm from fertile and infertile human ejaculate were fixed in 1% glutaraldehyde and treated histochemically to demonstrate calcium- and magnesium-dependent ATPase (Ca++- and Mg++-dependent). Furthermore, as substrates, ADP, AMP, and beta-glycerophosphate were used. The localization of Ca++-activated ATPase was not different from that of Mg++-activated ATPase. In the fertile human ejaculated sperm, ATPase activity was found on the surface of the acrosome and mitochondria consisting of the mitochondrial sheath, around the outer coarse fibers and in the axial filament complex. Compared with the result with fertile specimens, in the infertile human ejaculated sperm, ATPase activity on the motile structures, the outer coarse fibers, and the axial filament complex were considerably weaker and occasionally not recognized. From this study, it may be considered that ATPase around the outer coarse fibers and in the axial filament complex of sperm may serve to mediate contraction of the axonemal elements during motility. (Author's Modified)
 ...
PMID:[The cytochemical localization of ATPase activity in the spermatozoa from fertile and infertile human ejaculate by electron microscope (author's transl)]. 13 69

The bioflavonoid, quercetin, inhibited the (Na+, K+)adenosine triphosphatase purified from the electric organ of electric eel (Electrophorus electricus) or from lamb kidney. An analysis of its mode of action revealed that the formation of phosphoenzyme from Pi but not from ATP was inhibited. Quercetin increased the amount of ADP-sensitive phosphoenzyme (E1--P), indicating an inhibition of the conversion of E1--P to the ADP-insensitive form (E2--P). The rate of dephosphorylation of the phosphoenzyme formed from ATP was slowed by quercetin. These results suggest that quercetin inhibits the formation of E2--P from either Pi or E1-P as well as the hydrolysis of the phosphoenzyme. Its mode of action is therefore different from that of ouabain and other inhibitors of the Na+, K+)adenosine triphosphatase.
 ...
PMID:Inhibition of (Na+, K+)adenosine triphosphatase and its partial reactions by quercetin. 13 69

The kinetics of the Mg2+-dependent ATPase (adenosine triphosphatase) activity of bovine cardiac myosin and its papain subfragment-1 were studied by using steady-state and pre-steady-state techniques, and results were compared with published values for the corresponding processes in the ATPase mechanism of rabbit skeletal-muscle myosin subfragment-1. The catalytic-centreactivity for cardiac subfragment-1 is 0.019s-1, which is less than one-third of that determined for the rabbit protein. The ATP-induced isomerization process, measured from enhancement of protein fluorescence on substrate binding, is similarly decreased in rate, as is also the isomerization process associated with ADP release. However, the equilibrium constant for ATP cleavage, measured by quenched-flow by using [gamma-32P]ATP, shows little difference in the two species. Other experiments were carried out to investigate the rate of association of actin with subfragment-1 by light-scattering changes and also the rate of dissociation of the complex by ATP. The dissociation rate increases with increasing substrate concentration, to a maximum at high ATP concentrations, with a rate constant of about 2000s-1. It appears that isomerization processes which may involve conformational changes have substantially lower rate constants for the cardiac proteins, whereas equilibrium constants for substrate binding and cleavage are not significantly different. These differences may be related to the functional properties of these myosins in their different muscle types. Kinetic heterogeneity has been detected in both steady-state and transient processes, and this is discussed in relation to the apparent chemical homogeneity of cardiac myosin.
 ...
PMID:The magnesium-ion-dependent adenosine triphosphatase of bovine cardiac Myosin and its subfragment-1. 13 61

Delipidated dogfish rectal-gland Na++K+-ATPase (Na++K+-dependent adenosine triphosphatase), almost devoid of hydrolytic activity, is able to bind about 2nmol of ADP/mg of protein. The "affinity" of delipidated enzyme for ADP is not affected by K+ in concentrations that greatly decrease the "affinity" of native Na++K+-ATPase. The K+-sensitivity of the ADP binding is in part restored by relipidation with dioleoyl phosphatidylcholine.
 ...
PMID:Adenosine diphosphate binding to sodium-plus-potassium ion-dependent adenosine triphosphatase. The role of lipid in the nucleotide-potassium ion interplay. 13 21

Adenosine triphosphate (ATP) hydrolysis catalyzed by the plasma membrane (Na+,K+)ATPase isolated from several sources was inhibited by Mg+, provided that K+ and ATP were also present. Phosphorylation of the adenosine triphosphatase (ATPase) by ATP and by inorganic phosphate was also inhibited, as was p-nitrophenyl phosphatase activity. (Ethylenedinitrilo)tetraacetic acid (EDTA) and catecholamines protected from and reversed the inhibition of ATP hydrolysis by Mg2+, K+ and ATP. EDTA was protected by chelation of Mg2+ but catecholamines acted by some other mechanism. The specificities of various nucleotides as inhibitors (in conjunction with Mg2+ and K+) and as substrates for the (Na+, K+) ATPase were strikingly different. ATP, ADP, beta,gamma-CH2-ATP and alpha,beta-CH2-ADP were active as inhibitors, whereas inosine, cytidine, uridine, and guanosine triphosphates (ITP, CTP, UTP, and GTP) and adenosine monophosphate (AMP) were not. On the other hand, ATP and CTP were substrates and beta,gamma-NH-ATP was a competitive inhibitor of ATP hydrolysis, but not an inhibitor in conjunction with Mg2+ and K+. The Ca2+-ATPase from sarcoplasmic reticulum and F1, the Mg2+-ATPase from the inner mitochondrial membrane, were also inhibited by Mg2+. Catecholamines reversed inhibition of the Ca2+-ATPase, but not that of F1.
 ...
PMID:Reversible inhibition of (Na+, K+) ATPase by Mg2+, adenosine triphosphate, and K+. 13 42


1 2 3 4 5 6 7 8 9 10 Next >>