Phosphotungstate reagent

B 9. Explain the principles behind the use of the phosphotungstate reagent to measure HDL-cholesterol. 

The phosphotungstate reagent causes the precipitation of VLDL and LDL but HDL-cholesterol remains in solution. 

The color produced in the Lowry method results from the biuret reaction plus the reduction of the phosphomolybdate-phosphotungstate reagent (Folin CiOcalteu phenol reagent) by tyrosine residues. The Lowry method is suitable for solutions containing 20 to 400 /rg protein/ml. 

Use Intermediate in preparation of tungsten compounds, (e.g., phosphotungstate), reagent, fireproofing fabrics and cellulose, alkaloid precipitant. 

Into seven further 5 cm separatory funnels pipette 0.1, 0.5, 1.0, 2.0, 5.0, 7.5 and 10.0 cm of a 10 ppm toluene solution of the inhibitor which is being determined in the monomer sample (ie. additions of between 5 and 100 u g of inhibitor. Extract the sample funnel and the seven standard funnels with 20 cm distilled water then two 10 cm portions of distilled water and collect the 40 cm aqueous extracts in 50 cm Nessler cylinders (filtering if necessary). Dilute to 50 cm with water. To the sample and standard solutions add 2 cm sodium phosphotungstate reagent and 4 cm of sodium carbonate (10%) in this order and mix well after the addition of each reagent. Leave the solutions for 15 min and compare the depth of the blue colour obtained for the sample with that obtained from the various standard solutions. If necessary, repeat the run this time more closely bracketing the sample solution with the standards to obtain a better colour match between sample and standards. 

Assay of Adrenaline.—The hormone value of preparations may be estimated (i.) colorimetrically, by comparison of the blue colour it yields with Folin s phosphotungstate reagent (ii.) biologically, from the inhibitory effect on the contraction of a strip of involuntary muscle suspended in saline, the accelerating effect on an isolated heart, the dilating effect on a denervated iris, and the vaso-pressor response in an animal. 

Positive uric acid test (colors phosphotungstic reagent blue upon warming). 

The Folin-Denis assay is used as a procedure for the quantification of total phenolics in plant materials, food, and beverages. Reduction of phosphomolybdic-phosphotungstic acid (Folin-Denis reagent) to a blue-colored complex in an alkaline solution occurs in the presence of phenolic compounds (Folin and Denis 1912). 

Folin O, Denis W. 1912. On phosphotungstic-phosphomolybdic compounds as color reagents. J Biol Chem 12 239-243. 

Lowry method uses a combination of the Biuret copper-based reagent and the Folin-Ciocalteau reagent, which contains phosphomolybdic-phosphotungstic acid. Reagents react with protein, yielding a blue colour that displays an absorbance maximum at 750 nm... 

A standard Lowry-based protein assay has been adjusted to the special conditions encountered with skin [126], Basically, proteins reduce an alkaline solution of Cu(II)-tartrate to Cu(I) in a concentration-dependent manner. Then, the formation of a blue complex between Folin-Ciocalteau reagent (a solution of complex polymeric ions formed from phosphomolybdic and phosphotungstic heteropoly acids) and Cu(I) can be measured spectrophotometrically at 750 nm. A calibration curve can be obtained by dissolving known amounts of stratum corneum in 1 M sodium hydroxide. A piece of tape that has not been in contact with skin is subjected to an identical procedure and serves as negative control. The method was recently adapted to a 96-well plate format, notably reducing analysis times [129],... 

LDL precipitating reagent. This solution contains phosphotungstate, magnesium ions, and sodium azide. 

For small peptides, the amount of color increases with the size of the peptide. The presence of any of five amino acid residues (tyrosine, tryptophan, cysteine, histidine, and asparagine) in the peptide or protein backbone further enhance the amount of color produced, because they contribute additional reducing equivalents for further reduction of the phos-phomolybdic/phosphotungstic acid complex. With the exception of tyrosine and tryptophan, free amino acids will not produce a colored product with the Lowry reagent however, most dipeptides can be detected. In the absence of any of the five amino acids listed above, proteins containing proline residues have a lower... 

Folin, O., and Denis, W., 1912a, On phosphotungstic-phospomolybdic compounds as color reagents, J. Biol. Chem. 12 239-243. 

Phosphotungstic acid finds use in the precipitation of proteins, alkaloids, and certain amino acids. The solubility of sodium phosphotungstate, contrasted with the comparative insolubility of the potassium and ammonium salts, has suggested its use as a reagent in qualitative analysis. 

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