The binding of vanadium (V) oligoanions to sarcoplasmic reticulum

Abstract

The binding of monovanadate and decavanadate anions to sarcoplasmic reticulum vesicles was measured by equilibrium sedimentation. The affinity of vanadate binding and the molar amount of vanadium (V) bound at equilibrium is much greater with decavanadate than with monovanadate. The binding data can be rationalized in terms of one binding site per ATPase molecule for monovanadate and two sites per ATPase for decavanadate.The Ca-ATPase crystals formed with monovanadate and with decavanadate are similar in appearance, but decavanadate is particularly effective in promoting the crystallization of Ca2 +-ATPase at low V concentration (10-100 pM) in a Ca2+-free medium.Two-dimensional arrays of Ca2 +-transport ATPase molecules develop in sarcoplasmic reticulum vesicles exposed to Na3V04 in a Ca2+-free medium [l-91. Vanadate is assumed to bind with high affinity to the phosphate acceptor site of the Ca2+-ATPase; as a result the E2-vanadate complex accumulates with inhibition of ATPase activity and of the phosphorylation of the enzyme by inorganic orthophosphate [lo, 111. In agreement with this interpretation, interaction of Ca2+ with the high-affinity binding site of the Ca*+-ATPase prevents the formation of Ca2 + ATPase crystals and disrupts the crystals that were formed previously in the absence of calcium [ 1, 31. Inhibition of vanadate-induced crystallization was also observed in the presence of 5 mM Mg-ATP [l -31. Ca2+ and ATP are expected to stabilize the El conformation of the ATPase and therefore shift the equilibrium from the E2 toward the El form.The rate of crystallization of Ca2+-ATPase is markedly enhanced by increasing the vanadate concentration of the medium to 5 mM [l, 31; this is surprising since essentially complete inhibition of ATPase activity was observed at less than 0.5 mM vanadate concentration. These observations suggested that inhibition of ATPase activity through the formation of a kinetically stable E2-V enzyme complex may be a required but not sufficient condition for rapid crystallization to occur. There are at least two additional mechanisms that may be involved in the massive increase of the rate of crystallization of Ca2 +-ATPase at millimolar Na3V04 concentration. (a) Vanadate may bind to low-affinity sites on the Ca2+-ATPase, stabilizing the conformation that is most compatible with the formation of crystalline arrays. (b) The Ca2+-ATPase may interact with one or more of the large number of oligomeric vanadate species that accumulate in aqueous solutions containing millimolar concentrations of vanadium (V) at neutral pH [12-141. The tetrahedrally [12, 191, are inhibited only by the large octahedrally coordinated decameric vanadium (V) polyanion ; in these systems the monomeric vanadate anion, or its lower tetrahedral polyanionic species are ineffective. In the case of phosphorylase all oligomeric forms are inhibitory, while monomeric vanadate activates the enzyme slightly [20].Finally the K, of 4 nM for the inhibition of Na, K-ATPase by vanadate [21] strongly argues for monomeric vanad...

Decavanadate interactions with actin: cysteine oxidation and vanadyl formation

“…32, 33 The presence of calcium or ATP in the concentrations used in the assays did not change the decavanadate rate of decomposition (data not shown). The activation energy,…”

Influence of decavanadate on rat synaptic plasma membrane ATPases activity

“…In addition, extensive kinetic studies of porcine cerebral cortex Na + /K + -ATPase were undertaken to determine the nature of enzyme inhibition by V 10 . These enzymes were chosen because of their key role in normal functioning most cells of higher eukaryotic organisms (Scheiner-Bobis 2002) as well as pivotal roles in cancer cell migration (Lefranc et al 2008) and, on the other hand, known influence of V 10 on nucleotide-dependent enzymes (Boyd et al 1985;Csermely et al 1985;Varga et al 1985;Aureliano 2000;Pezza et al 2002;Aureliano and Gândara 2005).…”

Vanadium Complexes Are in vitro Inhibitors of Leishmania Secreted Acid Phosphatases

“…We have not been able to specifically determine the 'active' component but have shown that addition of V 10 does affect the activity of the phosphatase measured under specific acidic conditions using a well-established phosphatase substrate. It has long been known that decavanadate is unstable at low concentrations in aqueous solutions (Baes et al, 1976;Csermely et al, 1985;Varga et al, 1985;Chasteen, 1990;Crans et al, 2004). It is also well known that decavanadate solutions decompose at room temperature more quickly in buffer than in water Varga et al, 1985).…”

“…It has long been known that decavanadate is unstable at low concentrations in aqueous solutions (Baes et al, 1976;Csermely et al, 1985;Varga et al, 1985;Chasteen, 1990;Crans et al, 2004). It is also well known that decavanadate solutions decompose at room temperature more quickly in buffer than in water Varga et al, 1985). Despite the fact that decomposition studies predict only mononuclear vanadium (V) as the active form of the inhibitor, there is a clear difference in our studies in the Leishmania SAP activity response to V 10 relative to VO 4 3-with the same total vanadium concentration implying that different vanadium species are involved.…”