Vanadate dimers

Bond Distances and Angles for the [VO]2 Core of Various Dimeric Vanadate Complexes of Diols and a-Hydroxycarboxylic Acids... 

Rao, A.V.S., N.S. Islam, and T. Ramasarma. 1997. Reactivtiy of (X-peroxo-bridged dimeric vanadate in bromoperoxidation. Arch. Biochem. Biophys. 342 289-297. 

B. Redox decomposition of monoalkyl ester of dimeric vanadate, ROVO2-O-V03 , accompanied by two rapid successive one-electron transfers. Then, no free radical species are expected, and the products should be the carbonyl compound and VO. This mechanism has not yet been established for vanadate oxidations. 

The dimer chains of Ca -ATPase can also be observed by freeze-fracture electron microscopy [119,165,166,172-174], forming regular arrays of oblique parallel ridges on the concave P fracture faces of the membrane, with complementary grooves or furrows on the convex E fracture faces. Resolution of the surface projections of individual Ca -ATPase molecules within the crystalline arrays has also been achieved on freeze-dried rotary shadowed preparations of vanadate treated rabbit sarcoplasmic reticulum [163,166,173,175]. The unit cell dimensions derived from these preparations are a = 6.5 nm b = 10.7 nm and 7 = 85.5° [175], in reasonable agreement with earlier estimates on negatively stained preparations [88]. 

Fig. 4. Tentative allocation of probe binding sites within the three-dimensional structure of Ca -ATPase derived from vanadate-induced E2-type crystals. The top picture is the projection view of the Ca -ATPase down the x-axis, revealing the pear-shaped contours of ATPase molecules. The maximum length of the cytoplasmic domain to the tip of the lobe is =r65A. In the middle and bottom pictures the same structure is viewed down the x-axis, revealing the gap between the bridge and the bilayer surface and the connections between ATPase molecules in neighboring dimer chains. The proposed binding sites for lAEDANS and FITC are indicated. The bottom right picture is the same structure viewed down the y-axis. Adapted from Taylor et al. [90].

Antibody A52 with its epitope at residues 657-672 [129,139,274,275] inhibited the vanadate-induced crystallization of Ca " -ATPase and decreased the stability of preformed Ca " -ATPase crystals [285]. The vanadate-induced crystals arise by the association of the ATPase monomers into dimers (type A interaction), the dimers into dimer chains (type B interaction), and the dimer chains into 2-dimensional arrays (type C interaction). It is suggested that antibody A52 interferes with type B interactions, preventing the formation of dimer chains, without exerting major effect on the concentration of Ca -ATPase dimers in the membrane. The simplest interpretation of the destabilization of Ca -ATPase crystals by mAb A52 is that binding of the antibody to its antigenic site physically blocks the interaction between ATPase molecules [285]. Considering the large bulk of the antibody, such interference is not unexpected, yet only a few of the antibodies that bind to the Ca -ATPase in native sarcoplasmic reticulum interfered with crystallization. 

Reduction of 2-unsubstituted 1,3-dithiolylium salts, e.g. (354, R = H), with zinc (77JOC2778) or hexacarbonyl-vanadate (75JOC2002) leads to dimerization affording (355) the reduction of... 

These P-type ATPases are characterized by phosphoenzyme intermediates, by a conserved consensus sequence, and through inhibition by vanadate ion.537-539 The structures are poorly known. Some consist of single chains (perhaps dimerized) and some have more than one chain. However, the major subunit always appears to have about ten transmembrane helices with a large 430-residue cytoplasmic domain between the fourth and fifth helices. This domain contains the ATP binding site and the phosphoaspartyl group of the phosphoenzyme.534 This is Asp 369 for the Na+,K+- ATPase. 

Crans, D.C., C.D. Rithner, and L.A. Theisen. 1990. Application of time-resolved 51-V 2-D NMR for quantitation of kinetic exchange pathways between vanadate monomer, dimer, tetramer, and pentamer. J. Am. Chem. Soc. 112 2901-2908. 

Oxidation of one of the hydroxyl groups of a 1,2 glycol to form an a-hydroxy carboxylic acid increases the complexity of the vanadate chemistry. Mono, di, tri and higher nuclearity compounds are formed with a-hydroxy carboxylic acids. Except for the dimeric products, the structures adopted by these compounds are not known with any degree of certainty. 

Unlike ethylene glycol, a-hydroxycarboxylic acids, and p-mercaptoethanol, ligands such as ethanolamine, ethylenediamine, amino acids, and 2-aminoethanethiol do not form V2L2 complexes with vanadate [46], However, weakly formed products of VL stoichiometry (—546 ppm, —556 ppm) are observed with a number of a-amino acids [47], Because the amine functionality in amino acids is not suitable for formation of the cyclic [VN]2 core expected for a dimer, then one or the other of these VL compounds may correspond to the monomeric precursor to such a dimeric product. Certainly, with the a-hydroxycarboxylic acids, the monomeric complex can be a major component in solution. Similar VL complexes have not been reported for the amino alcohols. Perusal of the available reports suggests that the amine derivatives were studied under conditions where the nitrogen functionality was protonated, so the results may be somewhat misleading. 

The diaminohydroxybenzylate ligand, AL(<9rt/w-hydroxybenzyl)-./V,-(2-hydrox-yethyl)ethylenediamine, forms a dimeric water-stable complex with vanadate [51]. The dimer (Scheme 4.1a) has the [VO]2 central core found in many other V(V) complexes. The complex is unique in that the coordination about each vanadium is octahedral. In addition, each core oxygen is an oxo oxygen, a situation different... 

Crystal structures for both oxobispero [16] and oxobishydroxamido (bis(/V,/V-dieth-ylhydroxamido) [17]) and (bis(/V,/V-dimcthyIhydroxamido) [6]) vanadates have been reported. In both the peroxo and hydroxamido cases, the complexes occur as dimers... 

Paul, P.C., S J. Angus-Dunne, R.J. Batchelor, F.W.B. Einstein, and A.S. Tracey. 1997. Reactions of vanadate with N,N-dimethylhydroxylamine Aqueous equilibria and the crystal structure of the uncharged oxygen-bridged dimer of bis(N,N-dimethylhydrox-amido)hydroxooxovanadate. Can. J. Chem. 75 429-440. 

The reactions of a-hydroxycarboxylic acids with monoperoxovanadate are strikingly similar to those with vanadate itself. The predominant products are dimers that have the characteristic [VO]2 cyclic core. Structurally, the major difference between the two types of complexes is simply that one of the oxo groups (Scheme 6.9a) is replaced by a peroxo group to give a structure similar to that depicted in Scheme... 

Djordjevic, C., M. Lee, and E. Sinn. 1989. Oxoperoxo(citrato)vanadates(V) Synthesis, spectra, and structure of a hydroxyl oxygen bridged dimer, K2rV0(02)(C6H607)] 2H20. Inorg. Chem. 28 719-723. 

Ray, W.J., Jr., D.C. Crans, J. Zheng, J.W. Burgner, II, H. Deng, and M. Mahroof-Tahir. 1995. Structure of the dimeric ethylene glycol-vanadate complex and other 1,2-diol-vanadate complexes in aqueous solution Vanadate-based transition-state analog complexes of phosphotransferases. J. Am. Chem. Soc. 117 6015-6026. 

As described for the intramolecular systems, analyses of intermo-lecular exchange processes are also dependent on the mechanism of the reaction. A simple intermolecular exchange process is that between vanadate dimer (V2) and vanadate monomer (Vx). Two likely mechanisms for formation of dimer are shown in equations 7 and 8. The first involves the combination of two monomers (equation 7). The second involves the combination of monomer and dimer (equation 8). Recording 2D 51V EXSY spectra at a number of vanadate concentrations allows distinction between the two. A plot of the forward rate (fc(Vi—v2)[Vi]) as a function of [Vi]2 would be linear for equation 7 but not for equation 8. A linear... 

The X-ray structures of vanadium bromoperoxidases from the red seaweeds Corallina pilulifera and C. officinalis have also been determined and their structures are almost identical. The native structure of these enzymes is dodecameric and the structure is made up of 6 homo-dimers. The secondary stmcture of the chloroperoxidase from the ftmgus Curvularia inaequalis that will be discussed later can be superimposed with the Corallina hromoperoxidase dimer. Many of the a helices of each chloroperoxidase domain are structurally equivalent to the a helices in the Corallina hromoperoxidase dimer. This is in line with the evolutionary relationship between the haloperoxidases that will be discussed later. The disulfide bridges in the enzyme from A. nodosum are not found in the enzyme from Corallina and the two remaining cysteine residues are not involved in disulfide bonds. Additionally, in this enzyme binding sites are present for divalent cations that seem to be necessary to maintain the stmcture of the active site cleft. All the residues directly involved in the binding of vanadate are conserved in the algal bromoperoxidases. ... 

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