Showing papers on "Phosphotungstic acid published in 1974"

The role of phosphotungstic and phosphomolybdic acids in connective tissue staining I. Histochemical studies

Abstract: An investigation of the role of phosphotungstic and phosphomolybdic acids in Mallory-like trichrome methods showed unexpectedly that, rather than acting as mordants to anionic dyes, these polyacids selectively blocked staining of all tissue components other than connective tissue fibres to Aniline Blue and other similar fibrereactive dyes. Connective tissue components were found to contain residues resembling histidine that are easily accessible to anionic dyes. Blocking towards typical anionic dyes for demonstrating plasma proteins, such as Biebrich Scarlet, was also demonstrated but was less complete. The blockade of both types of dye was labile if the staining times were extended; plasma dyes were more sensitive than fibre dyes in this respect. Histochemical reactions for tyrosine residues were blocked. In connective tissue, phosphotungstic acid did not block histidine residues demonstrable by the coupled tetrazonium reaction with previous iodination. Thus it is postulated that differential trichrome staining occurs by binding of Aniline Blue to basic residues in the connective tissue not blocked by phosphotungstic acid and subsequent replacement of the blocking agent by an anionic dye. The binding of phosphotungstic acid to both epithelium and connective tissue was demonstrated by the quenching of autofluorescence in these regions and by the reduction of the bound PTA to blue coloured products with titanium trichloride.

Brain ganglioside preparation: phosphotungstic acid precipitation as an alternative to dialysis.

Abstract: IN THE procedure commonly used for the isolation of brain gangliosides (Suzu~r, 1965) the tissue is homogenized in chloroform-methanol and the gangliosides are separated from the chloroform-methanol extract by partition into an upper aqueous layer. Dialysis is then used to separate the gangliosides from the small molecules extracted. This dialysis procedure has the disadvantages that it is time-consuming (3 days), that losses are incurred in the transfer procedures, that there is the possibility of loss of samples due to leakage of the dialysis sacs, and that materials in the dialysis membrane may interfer with assays used for gangliosides. Furthermore, KANFER & SPIELVOGEL (1973) have recently reported that gangliosides may pass through the dialysis membrane if their concentration inside the sac is too low. To circumvent these problems the use of phosphotungstic acid to precipitate gangliosides from aqueous solutions has been investigated in this study.

A Thermometric Investigation of the Reaction between Proteins and 12-Phosphotungstic Acid

Abstract: Proteins in acid solution may be precipitated by the addition of a wide variety of anions including perchlorate, trifluoroacetate and tungstate(l). We have recently developed (2) a thermometric titration procedure for total serum protein based on their quantitative precipitation by 12-phosphotungstic acid (H3PW12O40). End point precision was~0 .5% when the total protein concentration was in the range of 1–10 g/l. Outside this range the precision deteriorates and the stoichiometry is not constant. At low protein concentration the reaction kinetics are too slow thereby inducing a positive error(3); while at high protein concentration the titration curve becomes quite nonlinear due to rather dramatic changes in the sample viscosity and concomitant changes in the rate of heat generation due to stirring (2).