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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A plasma membrane-bound adenosine triphosphatase with specific activities up to 0.2 micromol min(-1) (mg protein)(-1) at 80 degrees C was detected in the thermoacidophilic crenarchaeon Acidianus ambivalens (DSM 3772). The enzymatic activity exhibited a broad pH-optimum in the neutral range with two suboptima at pH 5.5 and 7.0, respectively. Sulfite activation resulted in only one pH optimum at 6.25. In the presence of the divalent cations Mg2+ and Mn2+ the ATPase activity was maximal. Remarkably, the hydrolytic rates of GTP and ITP were substantially higher than for ATP. ADP and pyrophosphate were only hydrolyzed with small rates, whereas AMP was not hydrolyzed at all. Both activities could be weakly inhibited by the classical F-type ATPase inhibitor N,N'-dicyclohexylcarbodiimide, whereas azide had no influence at all. The classical inhibitor of V-type ATPases, nitrate, also exerted a small inhibitory effect. The strongly specific V-type ATPase inhibitor concanamycin A, however, showed no effect at all. The P-type ATPase inhibitor vanadate had no inhibitory effect on the ATPase activity at pH 7.0, whereas a remarkable inhibition at high concentrations could be observed for the activity at pH 5.5. Arrhenius plots for both membrane bound ATPase activities were linear up to 95 degrees C, reflecting the enormous thermostability of the enzyme.
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PMID:Functional characterization of an extremely thermophilic ATPase in membranes of the crenarchaeon Acidianus ambivalens. 1054 43

Numerous cytochemical studies have reported that calcium-activated adenosine triphosphatase (Ca2+-ATPase) is localized on the abluminal plasma membrane of mature brain endothelial cells. Since the effects of fixation and co-localization of ecto-ATPase have never been properly addressed, we investigated the influence of these parameters on Ca2+-ATPase localization in rat cerebral microvessel endothelium. Formaldehyde at 2% resulted in only abluminal staining while both luminal and abluminal surfaces were equally stained following 4% formaldehyde. Fixation with 2% formaldehyde plus 0.25% glutaraldehyde revealed more abluminal staining than luminal while 2% formaldehyde plus 0.5% glutaraldehyde produced vessels with staining similar to 4% and 2% formaldehyde plus 0.25% glutaraldehyde. The abluminal reaction appeared unaltered when ATP was replaced by GTP, CTP, UTP, ADP or when Ca2+ was replaced by Mg2+ or Mn2+ or p-chloromercuribenzoate included as inhibitor. But the luminal reaction was diminished. Contrary to previous reports, our results showed that Ca2+-specific ATPase is located more on the luminal surface while the abluminal reaction is primarily due to ecto-ATPase. The strong Ca2+-specific-ATPase luminal localization explains the stable Ca2+ gradient between blood and brain, and is not necessarily indicative of immature or pathological vessels as interpreted in the past.
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PMID:Calcium-dependent ATPase unlike ecto-ATPase is located primarily on the luminal surface of brain endothelial cells. 1093 19

The eukaryotic V-type adenosine triphosphatase (V-ATPase) is a multi-subunit membrane protein complex that is evolutionarily related to F-type adenosine triphosphate (ATP) synthases and A-ATP synthases. These ATPases/ATP synthases are functionally conserved and operate as rotary proton-pumping nano-motors, invented by Nature billions of years ago. In the first part of this review we will focus on recent structural findings of eukaryotic V-ATPases and discuss the role of different subunits in the function of the V-ATPase holocomplex. Despite structural and functional similarities between rotary ATPases, the eukaryotic V-ATPases are the most complex enzymes that have acquired some unconventional cellular functions during evolution. In particular, the novel roles of V-ATPases in the regulation of cellular receptors and their trafficking via endocytotic and exocytotic pathways were recently uncovered. In the second part of this review we will discuss these unique roles of V-ATPases in modulation of function of cellular receptors, involved in the development and progression of diseases such as cancer and diabetes as well as neurodegenerative and kidney disorders. Moreover, it was recently revealed that the V-ATPase itself functions as an evolutionarily conserved pH sensor and receptor for cytohesin-2/Arf-family GTP-binding proteins. Thus, in the third part of the review we will evaluate the structural basis for and functional insights into this novel concept, followed by the analysis of the potentially essential role of V-ATPase in the regulation of this signaling pathway in health and disease. Finally, future prospects for structural and functional studies of the eukaryotic V-ATPase will be discussed.
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PMID:Eukaryotic V-ATPase: novel structural findings and functional insights. 2450 15


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