1H and 51V NMR studies of the interaction of vanadate and 2-vanadio-3-phosphoglycerate with phosphoglycerate mutase

NMR and DFT studies of the complexation of W(VI) and Mo(VI) with 3-phospho-D-glyceric and 2-phospho-D-glyceric acids

Multinuclear ((1)H, (13)C, (17)O, (31)P, (95)Mo, (183)W) magnetic resonance spectroscopy (1D and 2D) has been used to study the complexation of molybdate(VI) and tungstate(VI) with 3-phospho-D-glyceric and 2-phospho-D-glyceric acids. 3-Phospho-D-glyceric acid forms four and five complexes, respectively, with molybdate and tungstate. These have MO(2)(2+) centres, and involve the carboxylate and the adjacent OH groups. Two isomeric 1:2 (metal-ligand) complexes are detected, in addition to one mononuclear species having MO(3) centres and involving the ligand in a tridentate chelation and a dominant 12:4 species with both tungstate(VI) and molybdate(VI). The dominant 12:4 species can be seen as two 1:2 complexes bound together in a ring through two diphosphometalate moieties, derived from heptamolybdate or heptatungstate, respectively, by inclusion of two phosphate groups from the ligands. Tungstate is also able to form an additional 2:1 tridentate species. 2-Phospho-D-glyceric acid does not interact with tungstate but is able to form one phosphomolybdate species with molybdate, which can be regarded as a heptamolybdate derivative. Density functional theory (DFT) calculations were performed for 1:2 complexes, including calculations on the relative energies of the 1:2 complexes detected in related systems, to validate previously proposed structures. The results are compared with those obtained from multinuclear NMR spectroscopy.

Decavanadate (V10 O28 6-) and oxovanadates: oxometalates with many biological activities

The decameric vanadate species V(10)O(28)(6-), also referred to as decavanadate, impact proteins, lipid structures and cellular function, and show some effects in vivo on oxidative stress processes and other biological properties. The mode of action of decavanadate in many biochemical systems depends, at least in part, on the charge and size of the species and in some cases competes with the simpler oxovanadate species. The orange decavanadate that contains 10 vanadium atoms is a stable species for several days at neutral pH, but at higher pH immediately converts to the structurally and functionally distinct lower oxovanadates such as the monomer, dimer or tetramer. Although the biological effects of vanadium are generally assumed to derive from monomeric vanadate or the vanadyl cation, we show in this review that not all effects can be attributed to these simple oxovanadate forms. This topic has not previously been reviewed although background information is available [D.C. Crans, Comments Inorg. Chem. 16 (1994) 35-76; M. Aureliano (Ed.), Vanadium Biochemistry, Research Signpost Publs., Kerala, India, 2007]. In addition to pumps, channels and metabotropic receptors, lipid structures represent potential biological targets for decavanadate and some examples have been reported. Decavanadate interact with enzymes, polyphosphate, nucleotide and inositol 3-phosphate binding sites in the substrate domain or in an allosteric site, in a complex manner. In mitochondria, where vanadium was shown to accumulate following decavanadate in vivo administration, nM concentration of decavanadate induces membrane depolarization in addition to inhibiting oxygen consumption, suggesting that mitochondria may be potential targets for decameric toxicity. In vivo effects of decavanadate in piscine models demonstrated that antioxidant stress markers, lipid peroxidation and vanadium subcellular distribution is dependent upon whether or not the solutions administered contain decavanadate. The present review summarizes the reports on biological effects of decavanadate and highlights the importance of considering decavanadate in evaluations of the biological effects of vanadium.

Copper(II) and oxovanadium(IV) complexes of D-3-phosphoglyceric acid

The complexes formed between D-3-phosphoglyceric acid and H(+), Cu(II) and VO(IV) were studied by pH-potentiometric and spectral (UV-Vis, EPR and CD) methods in order to describe the speciation of the metal ions and to determine the most probable binding modes in the complexes formed in these systems. The results show that, in the pH range between 2 and 4, mononuclear 1:1 complexes are formed through bidentate (MAH) or tridentate (MA) coordination of the ligand. At higher pH, when the proton competition for the central alcoholic-OH function decreases, alcoholate-bridged dinuclear species of composition M(2)A(2)H(-n) (n=1-3) become predominant. VO(IV) seems to have a higher tendency than Cu(II) to form such dinuclear complexes.

Polyanionic inhibitors of phosphoglycerate mutase: combined structural and biochemical analysis

The effects that the inhibitors inositol hexakisphosphate and benzene tri-, tetra- and hexacarboxylates have on the phosphoglycerate mutases from Saccharomyces cerevisiae and Schizosaccharomyces pombe have been determined. Their Kivalues have been calculated, and the ability of the inhibitors to protect the enzymes against limited proteolysis investigated. These biochemical data have been placed in a structural context by the solution of the crystal structures of S. cerevisiae phosphoglycerate mutase soaked with inositol hexakisphosphate or benzene hexacarboxylate. These large polyanionic compounds bind to the enzyme so as to block the entrance to the active-site cleft. They form multiple interactions with the enzyme, consistent with their low Kivalues, and afford good protection against limited proteolysis of the C-terminal region by thermolysin. The inositol compound is more efficacious because of its greater number of negative charges. The S. pombe phosphoglycerate mutase that is inherently lacking a comparable C-terminal region has higher Kivalues for the compounds tested. Moreover, the S. pombe enzyme is less sensititive to proteolysis, and the presence or absence of the inhibitor molecules has little effect on susceptibility to proteolysis.

Sulphate ions observed in the 2.12 A structure of a new crystal form of S. cerevisiae phosphoglycerate mutase provide insights into understanding the catalytic mechanism

The structure of a new crystal form of Saccharomyces cerevisiae phosphoglycerate mutase has been solved and refined to 2.12 A with working and free R-factors of 19.7 and 22.9 %, respectively. Higher-resolution data and greater non-crystallographic symmetry have produced a more accurate protein structure than previously. Prominent among the differences from the previous structure is the presence of two sulphate ions within each active site cleft. The separation of the sulphates suggests that they may occupy the same sites as phospho groups of the bisphosphate ligands of the enzyme. Plausible binding modes for 2,3-bisphosphoglycerate and 1, 3-bisphosphoglycerate are thereby suggested. These results support previous conclusions from mutant studies, highlight interesting new targets for mutagenesis and suggest a possible mechanism of enzyme phosphorylation.

A two-component affinity chromatography purification of Helix pomatia arylsulfatase by tyrosine vanadate

The inhibition of Helix pomatia arylsulfatase by the synergistic combination of N-acetyl-l-tyrosine ethyl ester and vanadate has been extended to affinity chromatography for purification. In the presence of vanadate, l-tyrosine ethyl ester (TEE), immobilized on CH-Sepharose 4B retained arylsulfatase from the digestive juice or lyophilized powder of H. pomatia. No enzyme was retained without vanadate or with arsenate or phosphate. Arylsulfatase was eluted from the column matrix by removing the vanadate to less than 50 microM with buffer containing EDTA to chelate the vanadate. Escherichia coli alkaline phosphatase and potato acid phosphatase, two enzymes which are inhibited by vanadate but not by the vanadate-TEE complex, were not retained by the immobilized TEE under any conditions used. The sulfatase activity was completely separated from contaminating glucuronidase activity present in the crude enzyme extracts. The Ki for the immobilized vanadate-TEE system was found to be 5.0 x 10(-7) M with a capacity of 25 mg/ml swollen gel. A purification of greater than 40-fold from the lyophilized powder of H. pomatia (Sigma Type H-5) was achieved using this technique. The Ki/Keq of other phenols with vanadate were determined in a 96-well plate format as an example of a rapid screening technique that could be extended to other phosphoryl and sulfuryl-transfer enzyme classes.

The bidirectional effect of vanadyl ion on the oxygen affinity of human hemoglobin

The bidirectional effects of vanadyl on the oxygen affinity of hemoglobin depend on the mole ratio of vanadyl to Hb(R). In low R, the vanadyl ion increases Hb's oxygen affinity due to DPG hydrolysis. The lowered oxygen affinity in higher R is mainly due to the reactive-oxygen-species, probably superoxide, induced oxidation of Fe(II)-Hb to Fe(III)-Hb. The conformation change due to vanadyl binding contribute also to the lowered oxygen binding, but is monotonously decreasing with increasing of R values.

Influence of vanadium(V) complexes on the catalytic activity of ribonuclease A. The role of vanadate complexes as transition state analogues to reactions at phosphate

The interactions of vanadate and its complexes of uridine, 5,6-dihydrouridine, and methyl β-D-ribofuranoside with bovine pancreatic ribonuclease A (RNase A) (EC 3.1.27.5) were studied by51V NMR spectroscopy and enzyme kinetics. From kinetic studies, it was found that neither inorganic vanadate nor the methyl β-D-ribofuranoside–vanadate complex significantly inhibited the RNase A catalyzed hydrolysis of uridine 2′,3′-cyclic monophosphate. The NMR binding studies were in full agreement with the kinetics studies and showed that neither inorganic vanadate nor the methyl β-D-ribofuranoside–vanadate complex was bound tightly by the enzyme. Approximate binding constants were (5.0 ± 1.0) × 10−7 M and (3.0 ± 0.6) × 10−6 M for the uridine–and 5,6-dihydrouridine–vanadate complexes, respectively. An induced-fit mechanism is suggested, in which the pyrimidine subsite of the active site of RNase A must be fully occupied for the enzyme to be able to tightly bind the transition state or transition state analog. Calculation of the binding energies of vanadate complexes in ribonuclease, phosphoglycerate mutase, and phosphoglucomutase revealed an excess of binding energy over the analogous phosphate derivative of about 25 kJ/mol for all enzymes, even though the binding constants themselves varied by about six orders of magnitude. This energy represents about 40% of that expected to be available for a trigonal-bipyramidal transition state and requires a reassessment of the role of vanadate as a transition state analogue for phosphate transfer. Key words: vanadate, ribonuclease, transition state, binding constants, phosphate analogues, kinetics.