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Vanadate

About: Vanadate is a research topic. Over the lifetime, 4497 publications have been published within this topic receiving 120109 citations. The topic is also known as: vanadate.


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Journal ArticleDOI
TL;DR: The squid neuronal Na+–Ca2+ exchanger, NCX-SQ1, has a potential protein kinase C phosphorylation site between transmembrane segments 3 and 4 and a tyrosine kinase site in the Ca2+ binding region (tyrosine 462) and is unique among exchanger sequences to date.
Abstract: We have cloned the squid neuronal Na+–Ca2+ exchanger, NCX-SQ1, expressed it in Xenopus oocytes, and characterized its regulatory and ion transport properties in giant excised membrane patches. The squid exchanger shows 58% identity with the canine Na+–Ca2+ exchanger (NCX1.1). Regions determined to be of functional importance in NCX1 are well conserved. Unique among exchanger sequences to date, NCX-SQ1 has a potential protein kinase C phosphorylation site (threonine 184) between transmembrane segments 3 and 4 and a tyrosine kinase site in the Ca2+ binding region (tyrosine 462). There is a deletion of 47 amino acids in the large intracellular loop of NCX-SQ1 in comparison with NCX1. Similar to NCX1, expression of NCX-SQ1 in Xenopus oocytes induced cytoplasmic Na+-dependent 45Ca2+ uptake; the uptake was inhibited by injection of Ca2+ chelators. In giant excised membrane patches, the NCX-SQ1 outward exchange current showed Na+-dependent inactivation, secondary activation by cytoplasmic Ca2+, and activation by chymotrypsin. The NCX-SQ1 exchange current was strongly stimulated by both ATP and the ATP-thioester, ATPγS, in the presence of F− (0.2 mM) and vanadate (50 μM), and both effects reversed on application of a phosphatidylinositol-4′,5′-bisphosphate antibody. NCX1 current was stimulated by ATP, but not by ATPγS. Like NCX1 current, NCX-SQ1 current was strongly stimulated by phosphatidylinositol-4′,5′-bisphosphate liposomes. In contrast to results in squid axon, NCX-SQ1 was not stimulated by phosphoarginine (5–10 mM). After chymotrypsin treatment, both the outward and inward NCX-SQ1 exchange currents were more strongly voltage dependent than NCX1 currents. Ion concentration jump experiments were performed to estimate the relative electrogenicity of Na+ and Ca2+ transport reactions. Outward current transients associated with Na+ extrusion were much smaller for NCX-SQ1 than NCX1, and inward current transients associated with Ca2+ extrusion were much larger. For NCX-SQ1, charge movements of Ca2+ transport could be defined in voltage jump experiments with a low cytoplasmic Ca2+ (2 μM) in the presence of high extracellular Ca2+ (4 mM). The rates of charge movements showed “U”-shaped dependence on voltage, and the slopes of both charge–voltage and rate–voltage relations (1,600 s−1 at 0 mV) indicated an apparent valency of −0.6 charges for the underlying reaction. Evidently, more negative charge moves into the membrane field in NCX-SQ1 than in NCX1 when ions are occluded into binding sites.

55 citations

Journal ArticleDOI
TL;DR: In this paper, Mg, al-layered double hydroxides (LDHs) exchanged with decavanadate and pyrovanadate anions have been prepared and characterized by elemental analysis, FTIR, PXRD, XPS and BET.
Abstract: Mg,Al-layered double hydroxides (LDHs) exchanged with decavanadate and pyrovanadate anions have been prepared and characterized by elemental analysis, FTIR, PXRD, XPS and BET. The mixed oxide materials obtained by calcination at 823 K differ in catalytic performance depending on the type of intercalated vanadate. The activity of the calcined decavanadate-exchanged LDH is, depending on temperature, comparable or slightly better than that of the reference V–Mg--O sample, while its areal activity is much higher, pointing to the formation of centres of higher intrinsic activity. The activity of catalyst obtained from pyrovanadate-exchanged LDH is low. Selectivity-conversion profiles indicate that propene formed in the reaction is subsequently oxidized mainly to CO, the process being favoured over catalyst derived from the decavanadate-exchanged LDH. The selectivity pattern is related to the catalysts acid–base properties.

55 citations

Journal ArticleDOI
TL;DR: Inhibition of the myosin subfragment 1 (S-1) ATPase activity by beryllium fluoride was studied directly in the presence of MgATP and following preincubation of samples with MgADP, and it was concluded that M.ADP.BeF3- is analogous to the M++.
Abstract: Inhibition of the myosin subfragment 1 (S-1) ATPase activity by beryllium fluoride was studied directly in the presence of MgATP and following preincubation of samples with MgADP. In both cases, the rates of inhibition were very slow, with kapp = 0.5 and 58 M-1 s-1, respectively, in analogy to the rates of inhibition of myosin ATPase by vanadate [Goodno, C. C. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 2620-2624]. The very different rates of inhibition in the presence of MgATP and on preincubation with MgADP suggested that beryllium fluoride binds to the M.ADP state of myosin. The slow inhibition rates and the nonlinear dependence of the observed rates on beryllium fluoride concentration were consistent with a two-step inhibition process involving a rapid binding equilibrium to yield a collisional complex, M.ADP.BeF3-, and its slow isomerization into M++.ADP.BeF3-. A third, much slower, step was required to account for the conversion of the stable M++.ADP.BeF3- to a virtually irreversibly inhibited complex. Kinetic description of the inhibition pathway was derived from the observed rates of inhibition of myosin ATPase, information on the binding of beryllium fluoride to M.ADP, and measurements of epsilon ADP chase from M++.epsilon ADP.BeF3-. The isomerization rate and equilibrium constants were 1.4 x 10(-2) s-1 and 50, respectively, and the overall binding constant of beryllium fluoride to M.ADP was 5 x 10(5) M-1. The inhibitory complex showed a 16% enhancement to tryptophan fluorescence of S-1 and a reduced quenching of epsilon ADP by acrylamide. It is concluded that M++.ADP.BeF3- is analogous to the M++.ADP.Vi and M**.ADP.Pi states of myosin.

55 citations

Journal ArticleDOI
Otto Hansen1
TL;DR: In the presence of Mg2+ vanadate was shown to facilitate ouabain binding to (Na+ + K+)-ATPase in much the same way as Pi does, and the hypothesis thatVanadate interacts with the phosphate site of the enzyme seems to be supported by ouABain binding experiments.

55 citations

Journal ArticleDOI
TL;DR: Data obtained with vanadate ion support the contention that this enzyme may play a role in the regulation of bone cell growth.
Abstract: Isolated bone cells in culture contain an enzyme capable of hydrolyzing the phosphate ester of phosphotyrosine. This enzyme, which we have termed phosphotyrosine phosphatase, has not previously been reported in bone. Some of its characteristics include: 1) maximum activity near physiological pH, 2) a Km for substrate of 52 microM, 3) marked inhibition by the phosphate analog vanadate ion, 4) activity correlation with bone cell alkaline phosphatase, and 5) regulation by bone target hormones. Data obtained with vanadate ion support the contention that this enzyme may play a role in the regulation of bone cell growth.

55 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023109
2022211
202178
202075
201996
201899