Vanadate phosphate compared

Acylphosphate formation is characteristic for P-type ATPases and involves the transfer of the y-phosphate of ATP to an aspartic acid residue to form a high-energy enzyme intermediate. The phosphorylated aspartic acid residue is located in the sequence DKTGT, which is universally conserved in all members of the P-type superfamily. By this criterion, CopA and CopB of En. hirae are clearly members of the P-type superfamily of ATPases and probably function by the same underlying mechanism. Vanadate sensitivity is another hallmark of P-type ATPases. CopA and CopB were inhibited by vanadate with /50 values of around 0.1 mM. This is a low vanadate sensitivity compared to /50 values in the micromolar to submicromolar range observed for non-heavy metal P-type ATPases. 

Ammonium molybdate solution No precipitate is produced in the presence of ammonium nitrate and nitric acid, a soluble molybdovanadate being formed (compare phosphate). If the vanadate is mixed with a phosphate, much of the vanadium is coprecipitated with the ammonium phosphomolybdate. 

Table 2.5 provides an overview of the concentrations of important components of human blood, important in the sense that they constitute potential ligands for vanadium. The concentrations of lactate (1.5 mM) and citrate (0.1 mM) are comparatively high. Along with phosphate (1.2 mM), they are the major potential low molecular weight llgators for vanadate and vanadyl. The system containing vanadate(V) and lactate (lac) has been extensively smdled,[ °] and the species Identified on the basis of NMR and H+ potentiometry Include mono-, di-, trl- and tetranuclear forms, for which the structures... 

FTIR spectra of V04 in calcium phosphate/vanadate solid solutions show that V04 has C3V site symmetry at low vanadium contents, compared to Cs for pure vanadate. IR spectroscopy was used to characterise iron-containing CeV04 films (using vV = O at 770 cm ). ... 

Besides metal vanadates, other catalyst compositions were also tried in the past several decades. For instance, VPO based solids [101], FePO [102], MoVPO [103], heteropolyacids [104, 105], VPj/TiO [106, 107, 108], V-MOO [109] are widely used. Two isomorphous VOPO solids (a- and P ) were prepared and tested for the ammoxidation of 2MP to 2CPy [103, 110]. The reaction was carried out in the temperature range of 360 20°C. Between the two mono-phosphates tested, the a-VOPO showed better activity compared to P-VOP04. Interestingly, in situ synthesized 12-molybdophos-... 

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