Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.3.14 (ATP synthase)
 7,042 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The kinetic properties of type-II ATP diphosphohydrolase are described in this work. The enzyme preparation from the inner layer of the bovine aorta, mostly composed of smooth muscle cells, shows an optimum at pH 7.5. It catalyzes the hydrolysis of tri- and diphosphonucleosides and it requires either Ca2+ or Mg2+ for activity. It is insensitive to ouabain (3 mM), an inhibitor of Na+/K(+)-ATPase, to tetramisole (5 mM), an inhibitor of alkaline phosphatase, and to Ap5A (100 microM), an inhibitor of adenylate kinase. In contrast, sodium azide (10 mM), a known inhibitor for ATPDases and mitochondrial ATPase, is an effective inhibitor. Mercuric chloride (10 microM) and 5'-p-fluorosulfonylbenzoyl adenosine are also powerful inhibitors, both with ATP and ADP as substrates. The inhibition patterns are similar for ATP and DP, thereby, supporting the concept of a common catalytic site for these substrates. Apparent Km and Vmax, obtained with ATP as the substrate, were evaluated at 23 +/- 3 microM and 1.09 mumol Pi/min per mg protein, respectively. The kinetic properties of this enzyme and its localization as an ectoenzyme on bovine aorta smooth muscle cells suggest that it may play a major role in regulating the relative concentrations of extracellular nucleotides in blood vessels.
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PMID:Kinetic properties of type-II ATP diphosphohydrolase from the tunica media of the bovine aorta. 147 95

The Mg2+-ATPase activities of bovine adrenal chromaffin granules were studied in highly purified preparations of granule ghosts and in intact organelles. The overall ATPase activity (150-250 nmol ADP min-1 mg-1) of the granule ghost preparations was inhibited less than 5% by the bathophenanthroline chelate of Fe(II), a potent inhibitor of mitochondrial F1-ATPase. This small inhibition can be accounted for by a very minor contamination with mitochondria or mitochondrial fragments. The overall ATPase activity of native granule ghosts was inhibited about 75% by N-ethylmaleimide, with half-maximal inhibition at about 20 microM. The titration curve was slightly shifted towards higher concentrations as compared to the inhibition curve for the proton pump activity, which was completely inhibited at 25 microM. N,N'-Dicyclohexylcarbodiimide inhibited the overall ATPase activity by 75-80% at 1.1 mumol/mg protein, a concentration that completely abolished the proton pump activity. Low concentrations (10 microM) of vanadate inhibited the overall ATPase activity by about 15% but had no effect on the proton pump activity, which was partly inhibited only at higher vanadate concentrations. Our attempts to assign a function to the vanadate-sensitive and N-ethylmaleimide-insensitive ATPase have so far been unsuccessful. In particular, our assay for ATP diphosphohydrolase activity was negative, although the chromaffin granule ghosts revealed a low Mg2+-ADPase activity (11.8 nmol AMP min-1 mg-1 protein). In intact chromaffin granules the specific Mg2+-ATPase activity (50-70 nmol ADP min-1 mg-1) was stimulated 2-fold by uncouplers, as compared to 1.6-1.7-fold in granule ghosts. The degree of energy coupling was rather independent of the external pH (6.5 less than pH less than 8.0) and temperature (20-45 degrees C). As expected, partial inhibition (about 15%) of the overall ATPase activity by 10 microM vanadate increased the ATPase control ratio. ADP was found to be a potent inhibitor of the proton pump activity with MgATP as the substrate, and the effect can partly be explained by a competitive type of inhibition of the hydrolytic reaction. This effect of ADP explains some of the kinetic data reported for MgATP-dependent (H+-ATPase-dependent) reactions in this organelle, notably the energy-dependent accumulation and storage of catecholamines.
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PMID:Studies on Mg2+-dependent ATPase in bovine adrenal chromaffin granules. With special reference to the effect of inhibitors and energy coupling. 288 84

We studied the physiological role of flow through pulmonary arterioles in CO(2) gas exchange. We established human pulmonary arteriolar endothelial cells (HPAoEC). The cells demonstrated marked immunocytochemical staining of PECAM-1, VEGF R2, ACE-1, and CA type IV on their cell surface. Ten seconds shear stress stimulation caused the co-release of H(+) and ATP via the activation of F(1)/F(O) ATP synthase on the HPAoEC. F(1)/F(O) ATP synthase was immunocytochemically observed on the cell surface of non-permeabilized HPAoEC. In the shear stress-loaded HPAoEC culture media supernatant, ATPase activity increased in a time-dependent manner. The HPAoEC were strongly stained for NTPDase 1, which partially co-localized with purinergic P2Y1. The purinergic P2Y1 receptor agonist UTP (10(-6) M) significantly potentiated the shear stress-induced increase in ATPase activity in the culture medium supernatant. Ten seconds shear stress stimulation also produced stress strength-dependent CO(2) gas excretion from the HPAoEC, which was significantly reduced by the inhibition of F(1)/F(O) ATP synthase or CA IV on the endothelial cell (EC) surface. In conclusion, we have proposed a new concept of CO(2) exchange in the human lung, flow-mediated F(1)/F(O) ATP synthase-dependent H(+) secretion, resulting in the facilitation of a dehydration reaction involving HCO3(-) in plasma and the excretion of CO(2) gas from arteriolar ECs.
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PMID:Shear stress-mediated F1/FO ATP synthase-dependent CO2 gas excretion from human pulmonary arteriolar endothelial cells. 2176 65