Heteropoly molybdate complexes of flavin mononucleotide and some other phosphate esters

Solution structural studies of molybdate-nucleotide polyanions

The complexation of molybdate with the nucleotides adenosine-5'-monophosphate (5'-AMP), adenosine-3'-monophosphate (3'-AMP) and guanosine-5'-monophosphate (5'-GMP) has been investigated by (1)H and (31)P NMR and Mo K-edge X-ray absorption near edge (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Acidification of aqueous solutions containing molybdate and each of the nucleotides resulted in the formation of a single species characterized by (1)H resonances which are deshielded relative to those of free nucleotide. Analysis of the two-component systems indicated a Mo/nucleotide ratio of 2.5:1 for the complexation species. White compounds, characterized as Na(2)[Mo(5)O(15)(HB)(2)] (B=5'-AMP, 5'-GMP), have been isolated from the acidified molybdate/H(2)B solutions. Dissolution in D(2)O replicates the NMR spectra of the solution species observed prior to precipitation. Solution and solid state Mo K-edge XAS and EXAFS spectroscopy of Na(2)[Mo(5)O(15)(HAMP)(2)] and Na(6)[Mo(5)O(15)(PO(4))(2)] provide convincing evidence for the presence of a pentamolybdodiphosphate core in the molybdate-nucleotide complexes in both the solid and solution states.

Reactions of dysprosium with adenine nucleotides

Dysprosium catalyzes a rapid hydrolysis of both ATP and ADP, at ambient temperatures, pH 7.0, where no hydroxide precipitates. The reactive complexes, at pH 6.7, were found to contain 2Dy:1ATP and 3Dy:2ADP. AMP forms an insoluble complex containing 1Dy:2AMP, which does not hydrolyze. ATP also forms a soluble 1Dy:1ATP complex, which does not react. Dysprosium only catalyzes the hydrolysis of ATP above pH 5.8, where it has been titrated to the hydroxide. At the optimum pH (pH 7) the stoichiometric composition is Dy2.ATP.(OH)2, indicating that the active complex is neutral, whereas at pH 5.8 the stoichiometric composition is Dy2.ATP.(OH)+, indicating an inactive cationic complex. The mechanism proposed for the hydrolysis is consistent with those proposed for other in vitro systems known to catalyze the hydrolysis of ATP.

Partial purification and characterization of particulate acid phosphatase of Leishmania donovani promastigotes

1. More than 90% of the total acid phosphatase activity in a sonicate of L. donovani promastigotes is contained in a particulate fraction (200,000 X g 30 min). The enzyme can be quantitatively extracted and solubilized with the aid of Triton X-100 (0.2 g/100 ml) and purified over 200-fold with 54% yield by chromatography on DEAE-Sephadex, QAE-Sephadex, Sepharose 4B and concanavalin-A Sepharose. 2. The phosphatase is a true acid hydrolase (pH optimum, 5.0-5.5) and has a rather broad substrate specificity; it will catalyze the hydrolysis of 4-methylumbelliferylphosphate, thymolphthalein diphosphate, pyridoxal phosphate, fructose 1,6-diphosphate, glucose 6-phosphate, glucose 1-phosphate, ADP and AMP. 3. It is a large (170,000 daltons in the presence of Triton X-100), stable and acidic enzyme (pI = 4.1) that has the electrophoretic mobility of a type zero or type 1 isoenzyme in acid (pH 4.3) polyacrylamide gels. 4. The enzyme is inhibited by sodium fluoride, 2-mercaptoethanol and mumolar amounts of a number of polyanionic molybdenum and heavy metal complexes that include the following: [C(NH2)3]4[(C3H7O3PO3)2Mo5O15] X 3H2O, [C(NH2)3]2[(C6H5)2AsMo4O15H] X H2O, (NH4)4[SiMo12O40] X H2O and (NH4)6[P2Mo18O62] X 9H2O. 5. L. donovani promastigotes contain very low levels of 10 other acid pH optimum hydrolytic enzymes, with the exception of modest levels of alpha-fucosidase.