Determination of metal ion content of beverages and estimation of target hazard quotients: a comparative study

Background

Considerable research has been directed towards the roles of metal ions in nutrition with metal ion toxicity attracting particular attention. The aim of this study is to measure the levels of metal ions found in selected beverages (red wine, stout and apple juice) and to determine their potential detrimental effects via calculation of the Target Hazard Quotients (THQ) for 250 mL daily consumption.

Results

The levels (mean ± SEM) and diversity of metals determined by ICP-MS were highest for red wine samples (30 metals totalling 5620.54 ± 123.86 ppb) followed by apple juice (15 metals totalling 1339.87 ± 10.84 ppb) and stout (14 metals totalling 464.85 ± 46.74 ppb). The combined THQ values were determined based upon levels of V, Cr, Mn, Ni, Cu, Zn and Pb which gave red wine samples the highest value (5100.96 ± 118.93 ppb) followed by apple juice (666.44 ± 7.67 ppb) and stout (328.41 ± 42.36 ppb). The THQ values were as follows: apple juice (male 3.11, female 3.87), stout (male 1.84, female 2.19), red wine (male 126.52, female 157.22) and ultra-filtered red wine (male 110.48, female 137.29).

Conclusion

This study reports relatively high levels of metal ions in red wine, which give a very high THQ value suggesting potential hazardous exposure over a lifetime for those who consume at least 250 mL daily. In addition to the known hazardous metals (e.g. Pb), many metals (e.g. Rb) have not had their biological effects systematically investigated and hence the impact of sustained ingestion is not known.

Impairment of mineralization by metavanadate and decavanadate solutions in a fish bone-derived cell line

Vanadium, a trace metal known to accumulate in bone and to mimic insulin, has been shown to regulate mammalian bone formation using in vitro and in vivo systems. In the present work, short- and long-term effects of metavanadate (containing monomeric, dimeric, tetrameric and pentameric vanadate species) and decavanadate (containing decameric vanadate species) solutions on the mineralization of a fish bone-derived cell line (VSa13) were studied and compared to that of insulin. After 2 h of incubation with vanadate (10 microM in monomeric vanadate), metavanadate exhibited higher accumulation rates than decavanadate (6.85 +/- 0.40 versus 3.95 +/- 0.10 microg V/g of protein, respectively) in fish VSa13 cells and was also shown to be less toxic when applied for short periods. In longer treatments with both metavanadate and decavanadate solutions, similar effects were promoted: stimulation of cell proliferation and strong impairment (75%) of extracellular matrix (ECM) mineralization. The effect of both vanadate solutions (5 microM in monomeric vanadate), on ECM mineralization was increased in the presence of insulin (10 nM). It is concluded that chronic treatment with both vanadate solutions stimulated fish VSa13 cells proliferation and prevented ECM mineralization. Newly developed VSa13 fish cells appeared to be appropriate in the characterization of vanadate effects on vertebrate bone formation, representing a good alternative to mammalian systems.

Vanadate proliferative and anti-mineralogenic effects are mediated by MAPK and PI-3K/Ras/Erk pathways in a fish chondrocyte cell line

We recently reported proliferative and anti-mineralogenic effects of vanadate on fish chondrocytes and here we investigate the signalling pathways associated with these effects. Our data show that vanadate stimulates chondrocyte proliferation through the MAPK pathway, using signalling mechanisms similar to those used by IGF-1, while it inhibits chondrocyte differentiation/mineralization through a putative PI-3K/Ras/Erk signalling, a pathway shared with insulin. Our data also suggest that vanadate impairs ECM mineralization not only by interfering with regulatory pathways but also by inhibiting enzymatic activity of ALP. Finally, this work provides additional evidence for the conservation, throughout evolution, of mechanisms regulating chondrocyte proliferation and differentiation.

Vanadium and cadmium in vivo effects in teleost cardiac muscle: metal accumulation and oxidative stress markers

Several biological studies associate vanadium and cadmium with the production of reactive oxygen species (ROS), leading to lipid peroxidation and antioxidant enzymes alterations. The present study aims to analyse and compare the oxidative stress responses induced by an acute intravenous exposure (1 and 7 days) to a sub-lethal concentration (5 mM) of two vanadium solutions, containing different vanadate n-oligomers (n=1-5 or n=10), and a cadmium solution on the cardiac muscle of the marine teleost Halobatrachus didactylus (Lusitanian toadfish). It was observed that vanadium is mainly accumulated in mitochondria (1.33+/-0.26 microM), primarily when this element was administrated as decameric vanadate, than when administrated as metavanadate (432+/-294 nM), while the highest content of cadmium was found in cytosol (365+/-231 nM). Indeed, decavanadate solution promotes stronger increases in mitochondrial antioxidant enzymes activities (catalase: +120%; superoxide dismutase: +140%) than metavanadate solution. On contrary, cadmium increases cytosolic catalase (+111%) and glutathione peroxidases (+50%) activities. It is also observed that vanadate oligomers induce in vitro prooxidant effects in toadfish heart, with stronger effects induced by metavanadate solution. In summary, vanadate and cadmium are differently accumulated in blood and cardiac subcellular fractions and induced different responses in enzymatic antioxidant defence mechanisms. In the present study, it is described for the first time the effects of equal doses of two different metals intravenously injected in the same fish species and upon the same exposure period allowing to understand the mechanisms of vanadate and cadmium toxicity in fish cardiac muscle.

TNF-α acts via TNFR1 and muscle-derived oxidants to depress myofibrillar force in murine skeletal muscle

Tumor necrosis factor-α (TNF) diminishes specific force of skeletal muscle. To address the mechanism of this response, we tested the hypothesis that TNF acts via the type 1 (TNFR1) receptor subtype to increase oxidant activity and thereby depress myofibrillar function. Experiments showed that a single intraperitoneal dose of TNF (100 μg/kg) increased cytosolic oxidant activity ( P < 0.05) and depressed maximal force of male ICR mouse diaphragm by ∼25% within 1 h, a deficit that persisted for 48 h. Pretreating animals with the antioxidant Trolox (10 mg/kg) lessened oxidant activity ( P < 0.05) and abolished contractile losses in TNF-treated muscle ( P < 0.05). Genetic TNFR1 deficiency prevented the rise in oxidant activity and fall in force stimulated by TNF; type 2 TNF receptor deficiency did not. TNF effects on muscle function were evident at the myofibrillar level. Chemically permeabilized muscle fibers from TNF-treated animals had lower maximal Ca2+-activated force ( P < 0.02) with no change in Ca2+ sensitivity or shortening velocity. We conclude that TNF acts via TNFR1 to stimulate oxidant activity and depress specific force. TNF effects on force are caused, at least in part, by decrements in function of calcium-activated myofibrillar proteins.

Vanadate induces necrotic death in neonatal rat cardiomyocytes through mitochondrial membrane depolarization

Besides the well-known inotropic effects of vanadium in cardiac muscle, previous studies have shown that vanadate can stimulate cell growth or induce cell death. In this work, we studied the toxicity to neonatal rat ventricular myocytes (cardiomyocytes) of two vanadate solutions containing different oligovanadates distribution, decavanadate (containing decameric vanadate, V 10) and metavanadate (containing monomeric vanadate and also di-, tetra-, and pentavanadate). Incubation for 24 h with decavanadate or metavanadate induced necrotic cell death of cardiomyocytes, without significant caspase-3 activation. Only 10 microM total vanadium of either decavanadate (1 microM V 10) or metavanadate (10 microM total vanadium) was needed to produce 50% loss of cell viability after 24 h (assessed with MTT and propidium iodide assays). Atomic absorption spectroscopy showed that vanadium accumulation in cardiomyocytes after 24 h was the same when incubation was done with decavanadate or metavanadate. A decrease of 75% of the rate of mitochondrial superoxide anion generation, monitored with dihydroethidium, and a sustained rise of cytosolic calcium (monitored with Fura-2-loaded cardiomyocytes) was observed after 24 h of incubation of cardiomyocytes with decavanadate or metavanadate concentrations close to those inducing 50% loss of cell viability produced. In addition, mitochondrial membrane depolarization within cardiomyocytes, monitored with tetramethylrhodamine ethyl esther or with 3,3',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide, were observed after only 6 h of incubation with decavanadate or metavanadate. The concentration needed for 50% mitochondrial depolarization was 6.5 +/- 1 microM total vanadium for both decavanadate (0.65 microM V 10) and metavanadate. In conclusion, mitochondrial membrane depolarization was an early event in decavanadate- and monovanadate-induced necrotic cell death of cardiomyocytes.

Synthesis and biological evaluation of decavanadate Na4Co(H2O)6V10O28.18H2O

We have reported the synthesis and biological evaluation of a decavanadate Na(4)Co(H(2)O)(6)V(10)O(28).18H(2)O (CoV(10)) designed as a potential antitumoral agent. The human cancer cell lines SMMC-7721 (liver cancer) and SK-OV-3 (ovary cancer) were tested for their viability by the MTT method in vitro, which showed that the compound exhibited a remarkable activity against two cell lines with IC(50) values smaller than 0.24 microg/mL, 0.32 microg/mL, respectively. CoV(10) showed the tumor growth suppression for Hep-A-22 (mice liver cancer) in tumor bearing mice in vivo. In addition, using flow cytometry analysis, the ratio of apoptotic cells was up to 8.33% with treatment of CoV(10) at 1.56 microg/mL after 30 min, suggesting that the antitumoral activity of CoV(10) comes from the activation of the apoptotic pathway.

Peroxynitrite inhibits myofibrillar protein function in an in vitro assay of motility

We determined the effects of peroxynitrite (ONOO-) on cardiac myosin, actin, and thin filaments in order to more clearly understand the impact of this reactive compound in ischemia/reperfusion injury and heart failure. Actin filaments, native thin filaments, and alpha-cardiac myosin from rat hearts were exposed to ONOO- in the presence of 2 mM bicarbonate. Filament velocities over myosin, calcium sensitivity, and relative force generated by myosin were assessed in an in vitro motility assay in the absence of reducing agents. ONOO- concentrations > or =10 microM significantly reduced the velocities of thin filaments or bare actin filaments over alpha-cardiac myosin when any of these proteins were exposed individually. These functional deficits were linearly related to the degree of tyrosine nitration, with myosin being the most sensitive. However, at 10 microM ONOO- the calcium sensitivity of thin filaments remained unchanged. Cotreatment of myosin and thin filaments, analogous to the in vivo situation, resulted in a significantly greater functional deficit. The load supported by myosin after ONOO- exposure was estimated using mixtures experiments to be increased threefold. These data suggest that nitration of myofibrillar proteins can contribute to cardiac contractile dysfunction in pathologic states in which ONOO- is liberated.

Functional, structural, and chemical changes in myosin associated with hydrogen peroxide treatment of skeletal muscle fibers

To understand the molecular mechanism of oxidation-induced inhibition of muscle contractility, we have studied the effects of hydrogen peroxide on permeabilized rabbit psoas muscle fibers, focusing on changes in myosin purified from these fibers. Oxidation by 5 mM peroxide decreased fiber contractility (isometric force and shortening velocity) without significant changes in the enzymatic activity of myofibrils and isolated myosin. The inhibitory effects were reversed by treating fibers with dithiothreitol. Oxidation by 50 mM peroxide had a more pronounced and irreversible inhibitory effect on fiber contractility and also affected enzymatic activity of myofibrils, myosin, and actomyosin. Peroxide treatment also affected regulation of contractility, resulting in fiber activation in the absence of calcium. Electron paramagnetic resonance of spin-labeled myosin in muscle fibers showed that oxidation increased the fraction of myosin heads in the strong-binding structural state under relaxing conditions (low calcium) but had no effect under activating conditions (high calcium). This change in the distribution of structural states of myosin provides a plausible explanation for the observed changes in both contractile and regulatory functions. Mass spectroscopy analysis showed that 50 mM but not 5 mM peroxide induced oxidative modifications in both isoforms of the essential light chains and in the heavy chain of myosin subfragment 1 by targeting multiple methionine residues. We conclude that 1) inhibition of muscle fiber contractility via oxidation of myosin occurs at high but not low concentrations of peroxide and 2) the inhibitory effects of oxidation suggest a critical and previously unknown role of methionines in myosin function.

Understanding the mechanism of action of the novel SSAO substrate (C7NH10)6(V10O28).2H2O, a prodrug of peroxovanadate insulin mimetics

A new vanadium salt, hexakis(benzylammonium) decavanadate (V) dihydrate (C(7)NH(10))(6)(V(10)O(28)).2H(2)O (1), has been synthesized as well as characterized chemically and biologically. An in vitro enzyme assay revealed that compound 1 is oxidized to the same extent as a combination of benzylamine and vanadate by the enzyme semicarbazide-sensitive amine oxidase (SSAO), and therefore can be considered an SSAO substrate. It also stimulates glucose uptake in isolated rat adipocytes in a dose-dependent manner. We describe here the results of (51)V-NMR experiments that, combined with the in vitro results, corroborate that compound 1 could act as a prodrug of di-peroxovanadate ([V(OH)(2)(OO)(2)(OH)(2)](2-)) insulin mimetics.

Mitochondria as a target for decavanadate toxicity in Sparus aurata heart

In a previous in vivo study we have reported that vanadium distribution, antioxidant enzymes activity and lipid peroxidation in Sparus aurata heart are strongly dependent on the oligomeric vanadate species being administered. Moreover, it was suggested that vanadium is accumulated in mitochondria, in particular when V10 was intravenously injected. In this work we have done a comparative study of the effects of V10 and monomeric vanadate (V1) on cardiac mitochondria from S. aurata. V10 inhibits mitochondrial oxygen consumption with an IC(50) of 400 nM, while the IC(50) for V1 is 23 microM. V10 also induced mitochondrial depolarization at very low concentrations, with an IC(50) of 196 nM, and 55 microM of V1 was required to induce the same effect. Additionally, up to 5 microM V10 did inhibit neither F(0)F(1)-ATPase activity nor NADH levels and it did not affect respiratory complexes I and II, but it induced changes in the redox steady-state of complex III. It is concluded that V10 inhibits mitochondrial oxygen consumption and induces membrane depolarization more strongly than V1, pointing out that mitochondria is a toxicological target for V10 and the importance to take into account the contribution of V10 to the vanadate toxic effects.

Decavanadate induces mitochondrial membrane depolarization and inhibits oxygen consumption

Decavanadate induced rat liver mitochondrial depolarization at very low concentrations, half-depolarization with 39 nM decavanadate, while it was needed a 130-fold higher concentration of monomeric vanadate (5 microM) to induce the same effect. Decavanadate also inhibits mitochondrial repolarization induced by reduced glutathione in vitro, with an inhibition constant of 1 microM, whereas no effect was observed up to 100 microM of monomeric vanadate. The oxygen consumption by mitochondria is also inhibited by lower decavanadate than monomeric vanadate concentrations, i.e. 50% inhibition is attained with 99 M decavanadate and 10 microM monomeric vanadate. Thus, decavanadate is stronger as mitochondrial depolarization agent than as inhibitor of mitochondrial oxygen consumption. Up to 5 microM, decavanadate does not alter mitochondrial NADH levels nor inhibit neither F(O)F(1)-ATPase nor cytochrome c oxidase activity, but it induces changes in the redox steady-state of mitochondrial b-type cytochromes (complex III). NMR spectra showed that decameric vanadate is the predominant vanadate species in decavanadate solutions. It is concluded that decavanadate is much more potent mitochondrial depolarization agent and a more potent inhibitor of mitochondrial oxygen consumption than monomeric vanadate, pointing out the importance to take into account the contribution of higher oligomeric species of vanadium for the biological effects of vanadate solutions.

Vanadate-induced cell death is dissociated from H2O2 generation

Vanadium is an environmentally toxic metal with peculiar and sometimes contradictory cellular effects. It is insulin-mimetic, it can either stimulate cell growth or induce cell death, and it has both mutagenic and antineoplastic properties. However, the mechanisms involved in those effects are poorly understood. Several studies suggest that H(2)O(2) is involved in vanadate-induced cell death, but it is not known whether cellular sensitivity to vanadate is indeed related to H(2)O(2) generation. In the present study, the sensitivity of four cell lines from different origins (K562, K562-Lucena 1, MDCK, and Ma104) to vanadate and H(2)O(2) was evaluated and the production of H(2)O(2) by vanadate was analyzed by flow cytometry. We show that cell lines very resistant to H(2)O(2) (K562, K562-Lucena 1, and Ma104 cells) are much more sensitive to vanadate than MDCK, a cell line relatively susceptible to H(2)O(2), suggesting that vanadate-induced cytotoxicity is not directly related to H(2)O(2) responsiveness. In accordance, vanadate concentrations that reduced cellular viability to approximately 60-70% of the control (10 mumol/L) did not induce H(2)O(2) formation. A second hypothesis, that peroxovanadium (PV) compounds, produced once vanadate enters into the cells, are responsible for the cytotoxicity, was only partially confirmed because MDCK cells were resistant to both vanadate and PV compounds (10 micromol/L each). Therefore, our results suggest that vanadate toxicity occurs by two distinct pathways, one dependent on and one independent of H(2)O(2) production.

Binding modes of decavanadate to myosin and inhibition of the actomyosin ATPase activity

Decavanadate, a vanadate oligomer, is known to interact with myosin and to inhibit the ATPase activity, but the putative binding sites and the mechanism of inhibition are still to be clarified. We have previously proposed that the decavanadate (V(10)O(28)(6-)) inhibition of the actin-stimulated myosin ATPase activity is non-competitive towards both actin and ATP. A likely explanation for these results is that V(10) binds to the so-called back-door at the end of the Pi-tube opposite to the nucleotide-binding site. In order to further investigate this possibility, we have carried out molecular docking simulations of the V(10) oligomer on three different structures of the myosin motor domain of Dictyostelium discoideum, representing distinct states of the ATPase cycle. The results indicate a clear preference of V(10) to bind at the back-door, but only on the "open" structures where there is access to the phosphate binding-loop. It is suggested that V(10) acts as a "back-door stop" blocking the closure of the 50-kDa cleft necessary to carry out ATP-gamma-phosphate hydrolysis. This provides a simple explanation to the non-competitive behavior of V(10) and spurs the use of the oligomer as a tool to elucidate myosin back-door conformational changes in the process of muscle contraction.

Alterations to myofibrillar protein function in nonischemic regions of the heart early after myocardial infarction

Remote-zone left ventricular dysfunction (LVD) contributes to global reductions in contractile function after localized myocardial infarction (MI). However, the molecular mechanisms underlying this form of LVD are not clear. This study tested the hypothesis that myofibrillar protein function is directly affected in remote-zone LVD early after MI. Cardiac myosin and native thin filaments were purified from mouse myocardium taken from both the nonnecrotic zone adjacent to and the nonischemic zone remote from an infarct induced by 1 h of coronary occlusion followed by 24 h of reperfusion. Thin filament velocities were measured using the in vitro motility assay. Results showed that overall function was significantly reduced in samples from both the adjacent (43 +/- 12% of control, n = 7) and remote (53 +/- 8% of control, n = 13) zones when compared with control proteins (P < 0.05). Myosin from the remote zone propelled control thin filaments at reduced velocities similar to those measured above. In contrast, the Ca(2+) sensitivity of remote-zone thin filaments over control myosin was unchanged from control thin filaments (half-maximal at pCa 6.32 +/- 0.08 and 6.27 +/- 0.06, respectively) but showed a 20% increase in velocity at saturating Ca(2+) that parallels an increase in tropomyosin phosphorylation. Myosin dysfunction may be related to oxidation of cysteines in the myosin heavy chains or carbonylation of myosin binding protein-C. We hypothesize that phosphorylation of tropomyosin may serve a compensatory role, augmenting contraction during periods of oxidative stress when myosin function is compromised.

Oxidation chemistry of adenosine-3', 5'-cyclic monophosphate at pyrolytic graphite eletrode

The voltammetric oxidation of adenosine-3',5'-cyclic monophosphate (3',5'-CAMP) has been studied in the pH range 2.13-10.07 using pyrolytic graphite electrode (PGE). Voltammetric, coulometric, spectral studies, and product characterization indicate that the oxidation of 3',5'-CAMP occurs in an EC reaction involving a 6H+, 6e process at pH 7.24. Electrooxidized products were seperated by semipreparative high performance liquid chromatography (HPLC) and were characterized by mp, 1HNMR, FTIR, and GC-mass as allantoin cyclic ribose monophosphate and 3 dimers as the major products. A detailed interpretation of the redox mechanism of 3',5'-CAMP also has been presented to account for the formation of various products.

1H and 51V NMR investigations of the molecular nature of implant-derived vanadium ions in osteoarthritic knee-joint synovial fluid

BACKGROUND

High field (1)H and (51)V NMR spectroscopies were employed to determine the oxidation state and complexation status of vanadium ions in intact osteoarthritic knee-joint synovial fluid (OA SF) when pre-added as V(III)((aq.)), V(IV)((aq.)) and V(V)((aq.)).

METHODS

Aliquots of each vanadium solution were added to the SF samples and their (1)H NMR spectra recorded. (51)V NMR spectra were also recorded for the samples to which V(III)((aq.)) had been added. Theoretical computer simulations of the competitive complexation of vanadium ions by a range of low-molecular-mass biomolecules were also performed.

RESULTS

The spectroscopic results demonstrated that addition of vanadium ions to intact OA SF gave rise to their complexation by a range of low-molecular-mass biomolecules. The results indicated the physiologically-significant complexing abilities of histidine, threonine, glycine, tyrosine and citrate for each of the added metal ions. The computer simulations revealed that the relative capacity of OA SF complexants to compete for available V(III), V(IV) and V(V) ions reflected the thermodynamic stability constants for such complexes and their available concentrations in this biofluid.

CONCLUSIONS

Since comparatively low concentrations of added metal ion are required to selectively influence spectral properties, the "speciation" of prostheses-derived metal ions in biofluids and tissues can be ascertained through the facile employment of high resolution NMR spectroscopy.

Myosin light chain phosphorylation inhibits muscle fiber shortening velocity in the presence of vanadate

We have shown that myosin light chain phosphorylation inhibits fiber shortening velocity at high temperatures, 30 degrees C, in the presence of the phosphate analog vanadate. Vanadate inhibits tension by reversing the transition to force-generating states, thus mimicking a prepower stroke state. We have previously shown that at low temperatures vanadate also inhibits velocity, but at high temperatures it does not, with an abrupt transition in inhibition occurring near 25 degrees C (E. Pate, G. Wilson, M. Bhimani, and R. Cooke. Biophys J 66: 1554-1562, 1994). Here we show that for fibers activated in the presence of 0.5 mM vanadate, at 30 degrees C, shortening velocity is not inhibited in dephosphorylated fibers but is inhibited by 37 +/- 10% in fibers with phosphorylated myosin light chains. There is no effect of phosphorylation on fiber velocity in the presence of vanadate at 10 degrees C. The K(m) for ATP, defined by the maximum velocity of fibers partially inhibited by vanadate at 30 degrees C, is 20 +/- 4 microM for phosphorylated fibers and 192 +/- 40 microM for dephosphorylated fibers, showing that phosphorylation also affects the binding of ATP. Fiber stiffness is not affected by phosphorylation. Inhibition of velocity by phosphorylation at 30 degrees C depends on the phosphate analog, with approximately 12% inhibition in fibers activated in the presence of 5 mM BeF(3) and no inhibition in the presence of 0.25 mM AlF(4). Our results show that myosin phosphorylation can inhibit shortening velocity in fibers with large populations of myosin heads trapped in prepower stroke states, such as occurs during muscle fatigue.

H(2)O(2)-induced kinetic and chemical modifications of smooth muscle myosin: correlation to effects of H(2)O(2) on airway smooth muscle

The effect of H(2)O(2) on smooth muscle heavy meromyosin (HMM) and subfragment 1 (S1) was examined. The number of molecules that retained the ability to bind ATP and the actinactivated rate of P(i) release were measured by single-turnover kinetics. H(2)O(2) treatment caused a decrease in HMM regulation from 800- to 27-fold. For unphosphorylated and phosphorylated heavy meromyosin and for S1, approximately 50% of the molecules lost the ability to bind to ATP. H(2)O(2) treatment in the presence of EDTA protected against ATPase inactivation and against the loss of total ATP binding. Inactivation of S1 versus time correlated to a loss of reactive thiols. Treatment of H(2)O(2)-inactivated phosphorylated HMM or S1 with dithiothreitol partially reactivated the ATPase but had no effect on total ATP binding. H(2)O(2)-inactivated S1 contained a prominent cross-link between the N-terminal 65-kDa and C-terminal 26-kDa heavy chain regions. Mass spectral studies revealed that at least seven thiols in the heavy chain and the essential light chain were oxidized to cysteic acid. In thiophosphorylated porcine tracheal muscle strips at pCa 9 + 2.1 mM ATP, H(2)O(2) caused a approximately 50% decrease in the amplitude but did not alter the rate of force generation, suggesting that H(2)O(2) directly affects the force generating complex. Dithiothreitol treatment reversed the H(2)O(2) inhibition of the maximal force by approximately 50%. These data, when compared with the in vitro kinetic data, are consistent with a H(2)O(2)-induced loss of functional myosin heads in the muscle.

Decavanadate interactions with actin: inhibition of G-actin polymerization and stabilization of decameric vanadate

Decameric vanadate species (V10) inhibit the rate and the extent of G-actin polymerization with an IC50 of 68+/-22 microM and 17+/-2 microM, respectively, whilst they induce F-actin depolymerization at a lower extent. On contrary, no effect on actin polymerization and depolymerization was detected for 2mM concentration of "metavanadate" solution that contains ortho and metavanadate species, as observed by combining kinetic with (51)V NMR spectroscopy studies. Although at 25 degrees C, decameric vanadate (10 microM) is unstable in the assay medium, and decomposes following a first-order kinetic, in the presence of G-actin (up to 8 microM), the half-life increases 5-fold (from 5 to 27 h). However, the addition of ATP (0.2mM) in the medium not only prevents the inhibition of G-actin polymerization by V10 but it also decreases the half-life of decomposition of decameric vanadate species from 27 to 10h. Decameric vanadate is also stabilized by the sarcoplasmic reticulum vesicles, which raise the half-life time from 5 to 18h whereas no effects were observed in the presence of phosphatidylcholine liposomes, myosin or G-actin alone. It is proposed that the "decavanadate" interaction with G-actin, favored by the G-actin polymerization, stabilizes decameric vanadate species and induces inhibition of G-actin polymerization. Decameric vanadate stabilization by cytoskeletal and transmembrane proteins can account, at least in part, for decavanadate toxicity reported in the evaluation of vanadium (V) effects in biological systems.

Peroxynitrite diminishes myogenic tone in cerebral arteries: role of nitrotyrosine and F-actin

This study investigated the effect of peroxynitrite (OONO(-))-induced nitrosylation of filamentous (F)-actin on myogenic tone in isolated and pressurized posterior cerebral arteries (PCAs). Immunohistochemical staining was used to determine 3-nitrotyrosine (NT) and F-actin content in vascular smooth muscle after exposure to 10(-7) M or 10(-4) M OONO(-) for 5 or 60 min in isolated third-order PCAs (n = 37) from male Wistar rats pressurized to 75 mmHg in an arteriograph chamber, quantified with confocal microscopy. Additionally, the role of K(+) channels in OONO(-)-induced dilation was investigated with 3 microM glibenclamide or 10 mM tetraethylammonium chloride before OONO(-) exposure. OONO(-) (10(-4) M) induced a 40% dilation of tone (P < 0.05) while diminishing F-actin content by half (P < 0.05) and causing a 60-fold increase in NT (P < 0.05) in the vascular smooth muscle of PCAs. Additionally, F-actin was inversely correlated with both diameter and NT content (P < 0.05) and was significantly colocalized in the vascular smooth muscle with NT (overlap coefficient = 0.8). The dilation to ONOO(-) was independent of K(+) channel activity and thiol oxidation as glibenclamide, tetraethylammonium chloride, and dithiothreitol had no effect on OONO(-)-induced dilation or F-actin or NT content in PCAs. Because NT was colocalized with F-actin, we hypothesize that OONO(-) induces nitrosylation of F-actin in vascular smooth muscle leading to depolymerization and the subsequent loss of myogenic tone, which may promote vascular damage during oxidative stress such as in ischemia and reperfusion injury.

Biological activity of vanadium compounds

Vanadium compounds are characterised by a broad spectrum of action in vivo and in vitro. Their insulin-mimetic activity is manifested in their ability to normalize changes observed in both clinical and experimental diabetes (i.e. hyperglycaemia, hyperlipidaemia, lowered cell sensitivity to insulin) through the regulation of carbohydrate and lipid metabolism and the removal of secondary symptoms of this disease (as e.g. retinopathy, cardiomyopathy, nephropathy). Nevertheless, vanadium is considered to be a toxic element in both cationic and anionic form, although the latter type has more serious side effects. This is accounted for by the faster absorption of anionic forms, although the chemical structure, geometry, and the manner of synthesis of its derivatives also contributes to this elevated toxicity. Besides their antidiabetic properties, vanadium derivatives have also been observed to influence processes related to mitogenic cell responses (apoptosis, proliferation, neoplastic transformation). However, both anti-and pro-neoplastic properties of vanadium are reported.

Stress proteins (Hsp72/73, Grp94) expression pattern in rat organs following metavanadate administration. Effect of green tea drinking

Expression pattern of heat shock proteins (Hsp) 72/73 and glucose regulated protein (Grp) 94 was studied in liver, kidney and testis of rats injected with sublethal doses of ammonium metavanadate (5 mg/kg/day). In addition, some batches of animals were given green tea decoction, known to be rich in anti-oxidative compounds, as sole beverage in order to evaluate its protective properties. In control animals, the stress proteins expression was found to be organ-dependent: anti-Grp94 antibody revealed two bands at 96 and 98 kDa in kidney and liver whereas the 98 kDa band only was found in testis; anti-Hsp72/73 antibody revealed that the constitutive Hsp73 was present in all organs whereas the inducible Hsp72 was only present in kidney and testis. In kidney of vanadium-treated rats, Hsp73 was over-expressed by about 50% whereas Hsp72 was down-regulated by 50-80%. No such effects were observed in liver and testis. In liver and kidney of vanadium-treated rats, Grp94 was over-expressed by 50% and 150% respectively whereas no change was found in testis. In rats given green tea as sole beverage, the 96 kDa protein expression level in liver was reduced both in controls and in vanadium-treated animals. However, green tea drinking failed to prevent the vanadium-induced Hsp72 under-expression in kidney of vanadium-treated rats.

Hippocampal cell alterations induced by the inhalation of vanadium pentoxide (V(2)O(5)) promote memory deterioration

Spatial memory may be severely impaired as a consequence of ageing and neurodegenerative diseases, conditions that include neuronal damage. Vanadium (V) is a metalloid widely distributed in the environment and exerts severe toxic effects on a wide variety of biological systems. Reports about V inhalation toxicity on the CNS are limited, thus the purpose of this study is to determine the effects of Vanadium pentoxide (V(2)O(5)) inhalation (0.02M) on the memory and its correlation with the cytology of the hippocampus CA1. Forty eight CD-1 male mice were trained in spatial memory tasks and inhaled 1h twice a week; after each inhalation animals were evaluated and sacrificed from 1 to 4 weeks, perfused and processed for Golgi method and for ultrastructure evaluation. The cytological analysis consisted in counting the number of dendritic spines of 20 pyramidal neurons of hippocampus CA1, as well as ultrastructural characteristics. Results show that V inhalation produces a time dependent loss of dendritic spines, necrotic-like cell death, and notorious alterations of the hippocampus CA1 neuropile, which correlate with spatial memory impairment. Our data suggest that V induces important cellular and functional alterations, fact that deserves special attention since the concentration's trend of this element in the atmosphere is increasing.

Peroxynitrite induces F-actin depolymerization and blockade of myosin ATPase stimulation

Treatment of F-actin with the peroxynitrite-releasing agent 3-morpholinosydnonimine (SIN-1) produced a dose-dependent F-actin depolymerization. This is due to released peroxynitrite because it is not produced by 'decomposed SIN-1', and it is prevented by superoxide dismutase concentrations efficiently preventing peroxynitrite formation. F-actin depolymerization has been found to be very sensitive to peroxynitrite, as exposure to fluxes as low as 50-100nM peroxynitrite leads to nearly 50% depolymerization in about 1h. G-actin polymerization is also impaired by peroxynitrite although with nearly 2-fold lower sensitivity. Exposure of F-actin to submicromolar fluxes of peroxynitrite produced cysteine oxidation and also a blockade of the ability of actin to stimulate myosin ATPase activity. Our results suggest that an imbalance of the F-actin/G-actin equilibrium can account for the observed structural and functional impairment of myofibrils under the peroxynitrite-mediated oxidative stress reported for some pathophysiological conditions.

Vanadium distribution following decavanadate administration

An acute exposure of two vanadate solutions-metavanadate and decavanadate-containing different vanadate oligomers, induces different patterns of subcellular vanadium distribution in blood plasma, red blood cells (RBC), and cardiac muscle subcellular fractions of the fish Sparus aurata (gilthead seabream). The highest amount of vanadium was found in blood plasma 1 h after (5 mM) intravenous vanadate administration (295 +/- 64 and 383 +/- 104 microg V/g dry tissue, for metavanadate and decavanadate solutions, respectively), being 80-fold higher than in RBC. After 12 h of administration, the amount of vanadium in plasma, as well as in cardiac cytosol, decreased about 50%, for both vanadate solutions. During the period between 1 and 12 h, the ratio of vanadium in plasma/vanadium in RBC increased from 27 to 128 for metavanadate, whereas it remains constant (77) for decavanadate. Both vanadium solutions were primarily accumulated in the mitochondrial fraction (138 +/- 0 and 195 +/- 34 ng V/g dry tissue for metavanadate and decavanadate solutions, respectively, after 12 h exposure), rather than in cytosol. The amount of vanadium in cardiac mitochondria was twofold higher than in cytosol, earlier for metavanadate (6 h) than for decavanadate (12 h). It is concluded that, in fish cardiac muscle, the vanadium distribution is dependent on the administration of decameric vanadate, with vanadium being mainly distributed in plasma, before being accumulated into the mitochondrial fraction.

Dynamics of the upper 50-kDa domain of myosin V examined with fluorescence resonance energy transfer

The upper 50-kDa region of myosin may be critical for coupling between the nucleotide- and actin-binding regions. We introduced a tetracysteine motif in the upper 50-kDa domain (residues 292-297) of myosin V containing a single IQ domain (MV 1IQ), allowing us to label this site with the fluorescein biarscenical hairpin-binding dye (FlAsH) (MV 1IQ FlAsH). The enzymatic properties of MV 1IQ FlAsH were similar to those of unlabeled MV 1IQ except for a 3-fold reduced ADP-release rate. MV 1IQ FlAsH was also capable of moving actin filaments in the in vitro motility assay. To examine rotation of the upper 50-kDa region, we determined the difference in the degree of energy transfer from N-methylanthraniloyl (mant)-labeled nucleotides to FlAsH in both steady-state and transient kinetic experiments. The energy transfer efficiency was higher with mant-ATP (0.65 +/- 0.02) compared with mant-ADP (0.55 +/- 0.02) in the absence of actin. Stopped-flow measurements suggested that the energy transfer efficiency decreased with phosphate release (0.04 s(-1)) in the absence of actin. In contrast, upon mixing MV 1IQ FlAsH in the ADP.P(i) state with actin, a decrease in the energy transfer signal was observed at a rate of 13 s(-1), similar to the ADP release rate. Our results demonstrate there was no change in the energy transfer signal upon actin-activated phosphate release and suggest that actin binding alters the dynamics of the upper 50-kDa region, which may be critical for the ability of myosin to bind tightly to both ADP and actin.

Interactions of vanadium(V)-citrate complexes with the sarcoplasmic reticulum calcium pump

Among the biotargets interacting with vanadium is the calcium pump from the sarcoplasmic reticulum (SR). To this end, initial research efforts were launched with two vanadium(V)-citrate complexes, namely (NH(4))(6)[V(2)O(4)(C(6)H(4)O(7))(2)].6H(2)O and (NH(4))(6)[V(2)O(2)(O(2))(2)(C(6)H(4)O(7))(2)].4H(2)O, potentially capable of interacting with the SR calcium pump by combining kinetic studies with (51)V NMR spectroscopy. Upon dissolution in the reaction medium (concentration range: 4-0.5mM), both vanadium(V):citrate (VC) and peroxovanadium(V):citrate (PVC) complexes are partially converted into vanadate oligomers. A 1mM solution of the PVC complex, containing 184microM of the PVC complex, 94microM oxoperoxovanadium(V) (PV) species, 222microM monomeric (V1), 43microM dimeric (V2) and 53microM tetrameric (V4) species, inhibits Ca(2+) accumulation by 75 %, whereas a solution of the VC complex of the same vanadium concentration, containing 98microM of the VC complex, 263microM monomeric (V1), 64microM dimeric (V2) and 92microM tetrameric (V4) species inhibits the calcium pump activity by 33 %. In contrast, a 1 mM metavanadate solution, containing 460microM monomeric (V1), 90.2microM dimeric (V2) and 80microM tetrameric (V4) species, has no effect on Ca(2+) accumulation. The NMR signals from the VC complex (-548.0ppm), PVC complex (-551.5ppm) and PV (-611.1ppm) are broadened upon SR vesicle addition (2.5mg/ml total protein). The relative order for the half width line broadening of the NMR signals, which reflect the interaction with the protein, was found to be V4>PVC>VC>PV>V2=V1=1, with no effect observed for the V1 and V2 signals. Putting it all together the effects of two vanadium(V)-citrate complexes on the modulation of calcium accumulation and ATP hydrolysis by the SR calcium pump reflected the observed variable reactivity into the nature of key species forming upon dissolution of the title complexes in the reaction media.

Gating of TRP channels: a voltage connection?

TRP channels represent the main pathways for cation influx in non-excitable cells. Although TRP channels were for a long time considered to be voltage independent, several TRP channels now appear to be weakly voltage dependent with an activation curve extending mainly into the non-physiological positive voltage range. In connection with this voltage dependence, there is now abundant evidence that physical stimuli, such as temperature (TRPV1, TRPM8, TRPV3), or the binding of various ligands (TRPV1, TRPV3, TRPM8, TRPM4), shift this voltage dependence towards physiologically relevant potentials, a mechanism that may represent the main functional hallmark of these TRP channels. This review discusses some features of voltage-dependent gating of TRPV1, TRPM4 and TRPM8. A thermodynamic principle is elaborated, which predicts that the small gating charge of TRP channels is a crucial factor for the large voltage shifts induced by various stimuli. Some structural considerations will be given indicating that, although the voltage sensor is not yet known, the C-terminus may substantially change the voltage dependence of these channels.

Vanadate oligomers: in vivo effects in hepatic vanadium accumulation and stress markers

The formation of vanadate oligomeric species is often disregarded in studies on vanadate effects in biological systems, particularly in vivo, even though they may interact with high affinity with many proteins. We report the effects in fish hepatic tissue of an acute intravenous exposure (12, 24 h and 7 days) to two vanadium(V) solutions, metavanadate and decavanadate, containing different vanadate oligomers administered at sub-lethal concentration (5 mM; 1 mg/kg). Decavanadate solution promotes a 5-fold increase (0.135 +/- 0.053 microg V(-1) dry tissues) in the vanadium content of the mitochondrial fraction 7 days after exposition, whereas no effects were observed after metavanadate solution administration. Reduced glutathione (GSH) levels did not change and the overall reactive oxygen species (ROS) production was decreased by 30% 24 h after decavanadate administration, while for metavanadate, GSH levels increased 35%, the overall ROS production was depressed by 40% and mitochondrial superoxide anion production decreased 45%. Decavanadate intoxication did not induce changes in the rate of lipid peroxidation till 12 h, but later increased 80%, which is similar to the increase observed for metavanadate after 24 h. Decameric vanadate administration clearly induces different effects than the other vanadate oligomeric species, pointing out the importance of taking into account the different vanadate oligomers in the evaluation of vanadium(V) effects in biological systems.

Decavanadate effects in biological systems

Vanadium biological studies often disregarded the formation of decameric vanadate species known to interact, in vitro, with high-affinity with many proteins such as myosin and sarcoplasmic reticulum calcium pump and also to inhibit these biochemical systems involved in energy transduction. Moreover, very few in vivo animal studies involving vanadium consider the contribution of decavanadate to vanadium biological effects. Recently, it has been shown that an acute exposure to decavanadate but not to other vanadate oligomers induced oxidative stress and a different fate in vanadium intracellular accumulation. Several markers of oxidative stress analyzed on hepatic and cardiac tissue were monitored after in vivo effect of an acute exposure (12, 24 h and 7 days), to a sub-lethal concentration (5 mM; 1 mg/kg) of two vanadium solutions ("metavanadate" and "decavanadate"). It was observed that "decavanadate" promote different effects than other vanadate oligomers in catalase activity, glutathione content, lipid peroxidation, mitochondrial superoxide anion production and vanadium accumulation, whereas both solutions seem to equally depress reactive oxygen species (ROS) production as well as total intracellular reducing power. Vanadium is accumulated in mitochondria in particular when "decavanadate" is administered. These recent findings, that are now summarized, point out the decameric vanadate species contributions to in vivo and in vitro effects induced by vanadium in biological systems.

Decavanadate as a biochemical tool in the elucidation of muscle contraction regulation

Recently reported decameric vanadate (V(10)) high affinity binding site in myosin S1, suggests that it can be used as a tool in the muscle contraction regulation. In the present article, it is shown that V(10) species induces myosin S1 cleavage, upon irradiation, at the 23 and 74 kDa sites, the latter being prevented by actin and the former blocked by the presence of ATP. Identical cleavage patterns were found for meta- and decavanadate solutions, indicating that V(10) and tetrameric vanadate (V(4)) have the same binding sites in myosin S1. Concentrations as low as 50 muM decavanadate (5 muM V(10) species) induces 30% of protein cleavage, whereas 500 muM metavanadate is needed to attain the same extent of cleavage. After irradiation, V(10) species is rapidly decomposed, upon protein addition, forming vanadyl (V(4+)) species during the process. It was also observed by NMR line broadening experiments that, V(10) competes with V(4) for the myosin S1 binding sites, having a higher affinity. In addition, V(4) interaction with myosin S1 is highly affected by the products release during ATP hydrolysis in the presence or absence of actin, whereas V(10) appears to be affected at a much lower extent. From these results it is proposed that the binding of vanadate oligomers to myosin S1 at the phosphate loop (23 kDa site) is probably the cause of the actin stimulated myosin ATPase inhibition by the prevention of ATP/ADP exchange, and that this interaction is favoured for higher vanadate anions, such as V(10).

Decavanadate modulates gating of TRPM4 cation channels

We have tested the effects of decavanadate (DV), a compound known to interfere with ATP binding in ATP-dependent transport proteins, on TRPM4, a Ca(2+)-activated, voltage-dependent monovalent cation channel, whose activity is potently blocked by intracellular ATP(4-). Application of micromolar Ca(2+) concentrations to the cytoplasmic side of inside-out patches led to immediate current activation followed by rapid current decay, which can be explained by an at least 30-fold decreased apparent affinity for Ca(2+). Subsequent application of DV (10 microm) strongly affected the voltage-dependent gating of the channel, resulting in large sustained currents over the voltage range between -180 and +140 mV. The effect of DV was half-maximal at a concentration of 1.9 microm. The Ca(2+)- and voltage-dependent gating of the channel was well described by a sequential kinetic scheme in which Ca(2+) binding precedes voltage-dependent gating. The effects of DV could be explained by an action on the voltage-dependent closing step. Surprisingly, DV did not antagonize the effect of ATP(4-) on TRPM4, but caused a nearly 10-fold increase in the sensitivity of the ATP(4-) block. TRPM5, which is the most homologous channel to TRPM4, was not modulated by DV. The effect of DV was lost in a TRPM4 chimera in which the C-terminus was substituted with that of TRPM5. Deletion of a cluster in the C-terminus of TRPM4 containing positively charged amino acid residues with a high homology to part of the decavanadate binding site in SERCA pumps, completely abolished the DV effect but also accelerated desensitization. Deletion of a similar site in the N-terminus had no effects on DV responses. These results indicate that the C-terminus of TRPM4 is critically involved in mediating the DV effects. In conclusion, decavanadate modulates TRPM4, but not TRPM5, by inhibiting voltage-dependent closure of the channel.

Decavanadate binding to a high affinity site near the myosin catalytic centre inhibits F-actin-stimulated myosin ATPase activity

Decameric vanadate (V(10)) inhibits the actin-stimulated myosin ATPase activity, noncompetitively with actin or with ATP upon interaction with a high-affinity binding site (K(i) = 0.27 +/- 0.05 microM) in myosin subfragment-1 (S1). The binding of V(10) to S1 can be monitored from titration with V(10) of the fluorescence of S1 labeled at Cys-707 and Cys-697 with N-iodo-acetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine (IAEDANS) or 5-(iodoacetamido) fluorescein, which showed the presence of only one V(10) binding site per monomer with a dissociation constant of 0.16-0.7 microM, indicating that S1 labeling with these dyes produced only a small distortion of the V(10) binding site. The large quenching of AEDANS-labeled S1 fluorescence produced by V(10) indicated that the V(10) binding site is close to Cys-697 and 707. Fluorescence studies demonstrated the following: (i) the binding of V(10) to S1 is not competitive either with actin or with ADP.V(1) or ADP.AlF(4); (ii) the affinity of V(10) for the complex S1/ADP.V(1) and S1/ADP.AlF(4) is 2- and 3-fold lower than for S1; and (iii) it is competitive with the S1 "back door" ligand P(1)P(5)-diadenosine pentaphosphate. A local conformational change in S1 upon binding of V(10) is supported by (i) a decrease of the efficiency of fluorescence energy transfer between eosin-labeled F-actin and fluorescein-labeled S1, and (ii) slower reassociation between S1 and F-actin after ATP hydrolysis. The results are consistent with binding of V(10) to the Walker A motif of ABC ATPases, which in S1 corresponds to conserved regions of the P-loop which form part of the phosphate tube.

Cadmium and vanadate oligomers effects on methaemoglobin reductase activity from Lusitanian toadfish: in vivo and in vitro studies

Cadmium and two vanadate solutions as 'metavanadate' (containing ortho and metavanadate species) and 'decavanadate' (containing decameric species) (5 mM) were injected intraperitoneously in Halobatrachus didactylus (Lusitanian toadfish), in order to evaluate the effects of cadmium and oligomeric vanadate species on methaemoglobin reductase activity from fish red blood cells. Following short-term exposure (1 and 7 days), different changes were observed on enzyme activity. After 7 days of exposure, 'metavanadate' increased methaemoglobin reductase activity by 67% (P < 0.05), whereas, minor effects were observed on enzymatic activity upon cadmium and 'decavanadate' administration. However, in vitro studies indicate that decameric vanadate, in concentrations as low as 50 microM, besides strongly inhibiting methaemoglobin reductase activity, promotes haemoglobin oxidation to methaemoglobin. Although decameric vanadate species showed to be unstable in the different media used in this work, the rate of decameric vanadate deoligomerization is in general slow enough, making it possible to study its effects. It is concluded that the increase in H. didactylus methaemoglobin reductase activity is more pronounced upon exposition to 'metavanadate' than to cadmium and decameric species. Moreover, only decameric vanadate species promoted haemoglobin oxidation, suggesting that vanadate speciation is important to evaluate in vivo and in vitro effects on methaemoglobin reductase activity.

Oxidative stress in toadfish (Halobactrachus didactylus) cardiac muscle. Acute exposure to vanadate oligomers

Vanadate solutions as "metavanadate" (containing ortho and metavanadate species) and "decavanadate" (containing mainly decameric species) (5 mM; 1 mg/kg) were injected intraperitoneously in Halobatrachus didactylus (toadfish), in order to evaluate the contribution of decameric vanadate species to vanadium (V) intoxication on the cardiac tissue. Following short-term exposure (1 and 7 days), different changes on antioxidant enzyme activities-superoxide dismutase (SOD), catalase (CAT), selenium-glutathione peroxidase (Se-GPx), total glutathione peroxidase (GPx), lipid peroxidation and subcellular vanadium distribution were observed in mitochondrial and cytosolic fractions of heart ventricle toadfish. After 1 day of vanadium intoxication, SOD, CAT and Se-GPx activities were decreased up to 25%, by both vanadate solutions, except mitochondrial CAT activity that increased (+23%) upon decavanadate administration. After 7 days of exposure, decavanadate versus metavanadate solutions promoted different effects mainly on cytosolic CAT activity (-56% versus -5%), mitochondrial CAT activity (-10% versus +10%) and total GPx activity (+1% versus -35%), whereas lipid peroxidation products were significantly increased (+82%) upon 500 microM decavanadate intoxication. Accumulation of vanadium in total (0.137+/-0.011 microg/g) and mitochondrial (0.022+/-0.001 microg/g) fractions was observed upon 7 days of metavanadate exposure, whereas for decavanadate, the concentration of vanadium increased in cytosolic (0.020+/-0.005 microg/g) and mitochondrial (0.021+/-0.009 microg/g) fractions. It is concluded that decameric vanadate species are responsible for a strong increase on lipid peroxidation and a decrease in cytosolic catalase activity thus contributing to oxidative stress responses upon vanadate intoxication, in the toadfish heart.

ADP-insensitive phosphoenzyme intermediate of sarcoplasmic reticulum Ca(2+)-ATPase has a compact conformation resistant to proteinase K, V8 protease and trypsin

Sarcoplasmic reticulum Ca(2+)-ATPase was digested with proteinase K, V8 protease and trypsin in the absence of Ca(2+). Unphosphorylated enzyme was rapidly degraded. In contrast, ADP-insensitive phosphoenzyme formed with P(i) and phosphorylated state analogues produced by the binding of F(-) or orthovanadate, were almost completely resistant to the proteolysis except for tryptic cleavage at the T1 site (Arg(505)). The results indicate that the phosphoenzyme and its analogues have a very compact form in the cytoplasmic region, being consistent with large domain motions (gathering of three cytoplasmic domains). Results further show that the structure of the enzyme with bound decavanadate is very similar to ADP-insensitive phosphoenzyme. Thapsigargin did not affect the changes in digestion time course induced by the formation of the phosphorylated state analogues.

Distinct topologies of mono- and decavanadate binding and photo-oxidative cleavage in the sarcoplasmic reticulum ATPase

UV irradiation of the sarcoplasmic reticulum (SR) ATPase in the presence of vanadate cleaves the enzyme at either of two different sites. Under conditions favoring the presence of monovanadate, and in the presence of Ca(2+), ADP, and Mg(2+), cleavage results in two fragments of 71- and 38-kDa electrophoretic mobility. On the other hand, under conditions permitting formation of decavanadate, and in the absence of Ca(2+) and ADP, cleavage results in two fragments of 88- and 21-kDa electrophoretic mobility. The amino terminus resulting from cleavage is blocked and resistant to Edman degradation. However, the initial photo-oxidation product can be reduced with NaB(3)H(4,) resulting in incorporation of radioactive (3)H label. Extensive digestion of the labeled protein with trypsin then yields labeled peptides that are specific for the each of the photo-oxidation conditions, and can be sequenced after purification. Collection of the Edman reaction fractional products reveals the radioactive label and demonstrates that Thr(353) is the residue oxidized by monovanadate at the phosphorylation site (i.e. Asp(351)). Correct positioning of monovanadate at the phosphorylation site requires binding of Mg(2+) and ADP to the Ca(2+)-dependent conformation of the enzyme. Subsequent hydrolytic cleavage is likely assisted by the neighboring Asp(601), and yields the 71- and 38-kDa fragments. On the other hand, Ser(186) (and possibly the following three residues: Val(187), Ile(188), and Lys(189)) is the residue that is photo-oxidized by decavanadate in the absence of ADP. Hydrolytic cleavage of the oxidized product at this site is likely assisted by neighboring acidic residues, and yields the 88- and 21-kDa fragments. The bound decavanadate, which we find to produce steric interference with TNP-AMP binding, must therefore extend to the A domain (i.e. small cytosolic loop) in order to oxidize Ser(186). This protein conformation is only obtained in the absence of Ca(2+).

Interaction of saccharides with rare earth metal ions: synthesis and characterisation of Pr(III)- and Nd(III)-saccharide complexes

A number of complexes are synthesised with Pr(III) and Nd(III) employing the mono- and disaccharides, D-glucose, D-galactose, D-mannose, D-arabinose, D-ribose, D-xylose, maltose and lactose. The complexes are characterised by various spectral and analytical techniques, and based on these data, appropriate structures were assigned for all complexes.