Showing papers on "Vanadate published in 1978"

A Characterization of Vanadate Interactions with the (Na,K)-ATPase

Abstract: The interaction of vanadium in the +5 oxidation state (vanadate) with purified dog kidney Na+ and K+-stim- ulated adenosine trlphosphatase [(Na,K)-ATPase] has been studied using equilibrium binding, steady state kinetics, and measurements of relaxation kinetics. Van- adate binds to one high affinity site (Kl = 4 no) and one low afinity site (Kz = 0.5

Vanadate inhibits the red cell (Na + , K + ) ATPase from the cytoplasmic side

Abstract: THE enzyme (Na+, K+)ATPase exists in the plasma membrane of animal cells and maintains a high intracellular K+-to-Na+ ratio by coupling movement of these ions to the hydrolysis of ATP. This enzyme spans the plasma membrane1 and is asymmetrically positioned with the ATP hydrolysing site on the cytoplasmic side2. Cardiac glycosides inhibit the (Na+, K+)-ATPase by binding to the part of the enzyme facing the extracellular fluid3. Although there is considerable evidence that hormonal regulation of (Na+, K+)ATPase occurs in certain tissues4–8, no endogenous regulatory agents of the purified enzyme have been identified. Recently we discovered that vanadate (vanadium in the +5 oxidation state) inhibits purified (Na+, K+)ATPase from several tissues at concentrations of 10−7–10−8 M (refs 9,10). Vanadium has been established as a nutritional requirement in chickens and rats, and our estimates of the concentration of vanadium in muscle tissue (10−6–10−7 M) agree with concentrations measured in other tissues11. It is known that vanadate has properties similar to those of the phosphate ion12, and it therefore seemed likely that it might inhibit the enzyme by binding to the hydrolysis site which is on the cytoplasmic surface of the enzyme. We demonstrate here that vanadate is transported into the red cell and inhibits the (Na+, K +)ATPase from the cytoplasmic side.

Potent inhibition of dynein adenosinetriphosphatase and of the motility of cilia and sperm flagella by vanadate.

Abstract: The motility of demembranated sea urchin sperm flagella and that of embryo cilia reactivated with 0.1 mM ATP are completely inhibited by 4 micron and 0.5 micron vanadium(V) [V(V), in vanadate], respectively. The Mg2+-activated ATPase activity (ATP phosphohydrolase, EC 3.6.1.3)of the latent form of dynein 1 is inhibited 50% by 0.5-1 micron V(V), while the Ca2+-activated ATPase activity is much less sensitive. The inhibition of flagellar beat frequency and of dynein 1 ATPase activity by V(V) appears not to be competitive with ATP. In agreement with other reports, the inhibition of (Na,K)-ATPase by V(V) shows a slow onset in the presence of ATP and is relatively rapid in its absence. With dynein, however, the inhibition occurs at a rapid rate whether or not ATP is present. Catechol at a concentration of 1 mM reverses the V(V) inhibition of reactivated sperm motility, dynein ATPase, and (Na, K)-ATPase. Myosin and actomyosin ATPases show no inhibition by concentrations of V(V) up to 500 micron. The inhibition by V(V) provides a possible technique for distinguishing between the actions of dynein and myosin in different forms of cell motility.

Chromosome movement in lysed mitotic cells is inhibited by vanadate.

Abstract: Mitotic PtK1 cells, lysed at anaphase into a carbowax 20 M Brij 58 solution, continue to move chromosomes toward the spindle poles and to move the spindle poles apart at 50% in vivo rates for 10 min. Chromosome movements can be blocked by adding metabolic inhibitors to the lysis medium and inhibition of movement can be reversed by adding ATP to the medium. Vanadate at micromolar levels reversibly inhibits dynein ATPase activity and movement of demembranated flagella and cilia. It does not affect glycerinated myofibril contraction or myosin ATPase activty at less than millimolar concentrations. Vanadate at 10--100 micron reversibly inhibits anaphase movement of chromosomes and spindle elongation. After lysis in vanadate, spindles lose their fusiform appearance and become more barrel shaped. In vitro microtubule polymerization is insensitive to vanadate.

Commercial ATP containing traces of vanadate alters the response of (Na+ + K+) ATPase to external potassium.

Abstract: WE have reported that the puzzling inhibition of (Na+ + K+)ATPase preparations by K+ ions, at concentrations insufficient to displace Na+ ions from the intracellular Na+-loading sites, was observed only when Sigma ‘Sigma-grade’ ATP was used as a substrate1. The effect was attributed to a contaminant of the ATP, which bound to the enzyme reversibly but with a high affinity; and because ‘Sigma-grade’ ATP is unique in being prepared from muscle, we suggested that the inhibitor might have a physiological role. Similar conclusions were reached independently by Cantley and Josephson2,3, and they and their colleagues have now identified the contaminant as ortho-vanadate4. The inhibition of (Na+ + K+)ATPase by vanadate plus K+ ions is of interest both for its possible physiological significance—traces of vanadate occur widely in animal tissues5—and for its possible use in elucidating the mechanism of the sodium pump. From both points of view it is desirable to know whether the K+ ions act at the intracellular or extracellular surface of the membrane, and we report here experiments on resealed red cell ghosts showing that the action of K+ ions is at the extracellular surface. In the following paper, Cantley et al.6 describe experiments with intact red cells suggesting that the vanadate ions act at the intracellular surface.

Positive inotropism of vanadate in cat papillary muscle.

Abstract: MANY samples hf ‘Sigma grade’ ATP from Sigma Chemical Co. reportedly contained an impurity which induces anomalous kinetics of (Na, K)-ATPase activity1–3. This impurity has recently been identified as vanadate4, and shown to inhibit (Na, K)–ATPase from kidney4 and red blood cells5. These findings have received considerable interest because of a possible physiological role of vanadate as an endogenous regulator of (Na, K)–ATPase activity3–5. We now report that vanadate is capable of producing positive inotropic effects in electrically driven papillary muscles isolated from cats.

Vanadate-stimulated natriuresis.

Abstract: THE observation1–3 that V(v) is a potent inhibitor of (Na+, K+)-activated renal ATPase raised the possibility that it has natriuretic and thus diuretic properties in the living animal. We report here experiments showing that it has.

Metal catalysis in oxidation by peroxides. Part 3. Significance of ligand exchange and acid–base equilibria of vanadium(V) catalyst in oxidation by t-butyl hydroperoxide in alcohols

Abstract: Kinetic and spectroscopic evidence suggests that, in alcoholic solvents (ROH) and in the presence of t-butyl hydroperoxide, bis(acetylacetonato)oxovanadium(IV)[VO(acac)2] is rapidly converted to vanadate esters VO(OR)3. These vanadium(V) triesters undergo acid–base equilibria leading to anionic or cationic species depending on the acidity of the medium. Kinetic studies on the vanadium(V) catalysed oxidation of di-n-butyl sulphide by t-butyl hydroperoxide in methanol, ethanol, and propan-2-ol, respectively, at 25° indicate that the most active catalyst is the neutral species VO(OR)3. The significant depression of oxidation rates observed when vanadium anion species are present, even at low concentration, suggests that vanadium(V) species might be involved in aggregation phenomena which become more significant as the acidity decreases. Thus, the seemingly large differences observed in the rates of catalysed oxidation in the three alcohols mentioned stem from changes in the position of acid–base equilibria involving the catalyst species in the three solvents. Indeed, the dependence of oxidation rates upon the medium acidity shows that rather small differences in rates are found in the range where the neutral catalyst ester VO(OR)3 is the dominant species.

Spectra of europium-doped yttrium oxide and yttrium vanadate phosphors

Abstract: The spectral distributions of the visible absorption and fluorescence emission under electron beam excitation of Eu3+-doped (Y2O3) and (YVO4) powders have been detected and analyzed. (Y2O3: Eu3+) has a cubicC crystal structure with a unit cell dimension a=10·61 A. Its observed transitions from7 F 0 to many upper states have been recognized; the observed number of Stark components is in agreement with that based on theC 2 site symmetry of the Eu3+ ion in Y2O3. Eu3+-doped yttrium vanadate has a typical zircon tetragonal crystal structure with unit cell dimensions ofc=6·29 A anda=7·11 A. The observed transitions in (Eu3+: YVO4) have been identified and assigned in accordance with theD 2d site symmetry of the Eu3+ ion in this lattice.

Stabilizing titanium dioxide pigments with vanadates

Abstract: A process for the production of a light-stable and weather-stable titanium dioxide pigment comprising precipitating onto the pigment in aqueous suspension a colorless vanadate of at least one of zinc, magnesium, calcium, strontium and barium at a pH-value above 7 in about 0.01 to 5% by weight, expressed as V2 O5, based on TiO2. Advantageously the pigment either before or after precipitation of the vanadate is coated with at least one oxide, oxide hydrate or phosphate of titanium, silicon, aluminum or zirconium.

Electrolyte for low ohmic capacitor based on organic solvent - contg. ionogen also contains phosphoric acid and vanadate, molybdate and/or tungstate (NL 27.11.79)

Abstract: Electrolyte for low ohmic electrolytic capacitors with improved film-forming properties and increased spark potential is based on organic solvent (mixts.) (I) contg. dissolved ionogens (II), together with 0.01-0.1 mole H3PO4/kg solvent and a vanadate, molybdate and/or tungstate, pref. in an amt. between 0.005 wt.% and the limit of solubility at 110 degrees C.

Determination of thioacetamide with ceric sulphate, sodium vanadate, manganese (III), and potassium ferricyanide

Abstract: The determination of thioacetamide in sulphuric acid medium with ceric sulphate, sodium vanadate, manganese (III) and potassium ferricyanide is described. A mixture of potassium iodate and potassium iodide (iodine) is used as the catalyst to accelerate the reaction. Ferroin is used as the indicator.