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Vanadyl protein binding

Insulin binding to the extracellular side of cell membranes initiates the insulin cascade , a series of phosphorylation/dephosphorylation steps. A postulated mechanism for vanadium is substitution of vanadate for phosphate in the transition state structure of protein tyrosine phosphatases (PTP).267,268 In normal physiological conditions, the attainable oxidation states of vanadium are V111, Viv and Vv. Relevant species in solution are vanadate, (a mixture of HV042-/ H2VOO and vanadyl V02+. Vanadyl is not a strong inhibitor of PTPs, suggesting other potential mechanisms for insulin mimesis for this cation. [Pg.833]

Vanadate transport in the erythrocyte was shown to occur via facilitated diffusion in erythrocyte membranes and was inhibited by 4,4 -diisothiocyanostilbene-2,2 -disulfonic acid (DIDS), a specific inhibitor of the band 3 anion transport protein [23], Vanadium is also believed to enter cells as the vanadyl ion, presumably through cationic facilitated diffusion systems. The divalent metal transporter 1 protein (called DMT1, and also known as Nramp2), which carries iron into cells in the gastrointestinal system and out of endosomes in the transferrin cycle [24], has been proposed to also transport the vanadyl cation. In animal systems, specific transport protein systems facilitate the transport of vanadium across membranes into the cell and between cellular compartments, whereas the transport of vanadium through fluids in the organism occurs via binding to proteins that may not be specific to vanadium. [Pg.157]

Cannon, J. C., Chasteen, N. D. The Distinction between Metal Binding Sites in Vanadyl Transferrin Complexes in Proteins of Iron Storage and Transport in Biochemistry and Medicine, (ed.) Crichton, R. R, Amsterdam, North Holland Press, 1975... [Pg.137]

While the affinity of transferrin see Iron Proteins for Storage Transport their Synthetic Analogs) for vanadyl is 10-fold greater than that of albumin, the latter can bind up to 20 vanadyl ions including a specific interaction with cys-34, the only reduced cysteine residue in the protein. [Pg.5463]

Vanadium is an element, and as such, is not metabolized. However, in the body, there is an interconversion of two oxidation states of vanadium, the tetravalent form, vanadyl (V+4), and the pentavalent form, vanadate (V+5). Vanadium can reversibly bind to transferrin protein in the blood and then be taken up into erythrocytes. These two factors may affect the biphasic clearance of vanadium that occurs in the blood. Vanadate is considered more toxic than vanadyl, because vanadate is reactive with a number of enzymes and is a potent inhibitor of the Na+K+-ATPase of plasma membranes (Harris et al. 1984 Patterson et al. 1986). There is a slower uptake of vanadyl into erythrocytes compared to the vanadate form. Five minutes after an intravenous administration of radiolabeled vanadate or vandadyl in dogs, 30% of the vanadate dose and 12% of the vanadyl dose is found in erythrocytes (Harris et al. 1984). It is suggested that this difference in uptake is due to the time required for the vanadyl form to be oxidized to vanadate. When V+4 or V+5 is administered intravenously, a balance is reached in which vanadium moves in and out of the cells at a rate that is comparable to the rate of vanadium removal from the blood (Harris et al. 1984). Initially, vanadyl leaves the blood more rapidly than vandate, possibly due to the slower uptake of vanadyl into cells (Harris et al. 1984). Five hours after administration, blood clearance is essentially identical for the two forms. A decrease in glutathione, NADPH, and NADH occurs within an hour after intraperitoneal injection of sodium vanadate in mice (Bruech et al. 1984). It is believed that vanadate requires these cytochrome P-450 components for oxidation to the vanadyl form. A consequence of this action is the diversion of electrons from the monooxygenase system resulting in the inhibition of drug dealkylation (Bruech et al. 1984). [Pg.34]

Vanadium in the plasma can exist in a bound or unbound form (Bruech et al. 1984). Vanadium as vanadyl (Patterson et al. 1986) or vanadate (Harris and Carrano 1984) reversibly binds to human serum transferrin at two metalbinding sites on the protein. With intravenous administration of vanadate or vanadyl, there is a short lag time for vanadate binding to transferrin, but, at 30 hours, the association is identical for the two vanadium forms (Harris et al. 1984). The vanadium-transferrin binding is most likely to occur with the vanadyl form as this complex is more stable (Harris et al. [Pg.34]

Vanabins, storage proteins for the vanadyl cation found in ascidians, and containing up to 20 VO + attached to amine terminals of lysines (section 4.1.2 and Figure 4.4). A vanadium(IV)-binding protein was also isolated from the bacterium Pseudomonas isachenkovii (Section 4.5) which utilises vanadate as terminal electron acceptor in anaerobic respiration, and appears as well to be present in the hydrogen bacterium Xanthobacter autotrophicus. ... [Pg.182]

The binding of vanadate and vanadyl to the two main serum proteins (Alb and Tf) as studied by EPR and NMR spectroscopy exemplifies the analytical value of these spectroscopic probes when it comes to an evaluation of the coordination environment of a metal ion at a specific protein site, and the strength of the interaction. A large number of... [Pg.192]

The first structural elucidation of a naturally occurring vanadium compound has been achieved. Amavadine, which has been isolated from the fly Amanita muscaria, has been shown by degradative, synthetic, and spectroscopic studies to have the structure (32) (p.54). The use of the vanadyl group as a new spectroscopic probe of metal binding sites in proteins has been demonstrated by its incorporation into insulin. E.s.r., optical, and i.r. spectra of the protein-bound have indicated that it is held on two types of site the co-ordination geometry about the metal was determined in each case. This approach should be valuable in the study of other metalloproteins. ... [Pg.41]

Despite the excitanent generated by the X-ray structure, the localization of the biotinylated metal complex within the protein environment was a source of disappointment. Indeed, we anticipated that the active catalyst would be encapsulated within the biotin-binding pocket of Sav rather than on the surface of the protein. To overcome this problem we tested whether the polar residues present within the biotin-binding pocket itself may be capable of binding a polar coordination complex. With this goal in mind, we tested the catalytic potential of vanadyl as a catalyst. ... [Pg.371]


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