Sulfate-transfer

3 -Phosphoadenosine 5 -phosphosulfate is the coenzyme through which sulfate is activated and transferred. Acceptors include sugars polymerized 

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Opa.nte. There are two methods used at various plants in Russia for loparite concentrate processing (12). The chlorination technique is carried out using gaseous chlorine at 800°C in the presence of carbon. The volatile chlorides are then separated from the calcium—sodium—rare-earth fused chloride, and the resultant cake dissolved in water. Alternatively, sulfuric acid digestion may be carried out using 85% sulfuric acid at 150—200°C in the presence of ammonium sulfate. The ensuing product is leached with water, while the double sulfates of the rare earths remain in the residue. The titanium, tantalum, and niobium sulfates transfer into the solution. The residue is converted to rare-earth carbonate, and then dissolved into nitric acid. 

Transfer the residue derived from Section 6.1.1 or 6.1.2 into a 200-mL separatory funnel with 80 mL of water and add 5 g of sodium chloride. Adjust the pH of the aqueous phase to 6-8 with saturated aqueous sodium hydrogencarbonate solution. Extract the aqueous phase successively with 50 and 30 mL of dichloromethane by shaking the funnel with a mechanical shaker for 5 min. Combine the dichloromethane extracts and dry with anhydrous sodium sulfate. Transfer the extracts into a 100-mL round-bottom flask and concentrate the extracts to near dryness by rotary evaporation. Dissolve the residue in 2 mL of n-hexane. 

The mixture is tested for peroxide as follows Prepare an approximately 1% solution of ferrous ammonium sulfate. Transfer 5 ml to each of two test tubes and add 0.5 iriL of 0.5 M sulfuric acid and 0.5 iil. of 0.1 M potassium thiocyanate solution to each tube. Add 5 mL of the methylene chloride solution to one of the test tubes and shake well. The aqueous phase in the methylene chloride tube should not develop a brown red color when examined parallel to the blank. 

The activation mechanism of phosphosulfate linkages (P—O —S)has been studied to understand the chemistry of biological sulfate-transfer reactions of phosphosul-fates of adenosine (APS and PAPS). Several phosphosul-fates were prepared and subjected to several nucleophilic reactions including hydrolysis. In general, phosphosulfates are stable in neutral aqueous mediay but become labile under acidic conditions, resulting in selective S—O fission. This S—O fission appears to occur by unimolecular elimination of sulfur trioxide, which can react with a nucleophilic acceptor, leading to a sulfate-transfer reaction. This process can be accelerated by Mg2+ ion when the solvent is of low water content. Under neutral conditions, divalent metal ions also were found to catalyze nucleophilic reactions, but these occurred on phosphorus to result in exclusive P-O fission. 

Phosphosulfates may react with a nucleophile (Nu) in either of the two modes of P-O or S-O bond fission (Figure 2). If water is the nucleophile, both modes of fission result in the same hydrolysis products. Mechanistically, however, the enzymes that catalyze P—O fission may be regarded as phosphatases, while those that catalyze S—O fission are sulfohydrolases. In fact, many hydrolytic enzymes are assumed to be sulfohydrolases without mechanistic proof. The possibility that they might be phosphatases was suggested by Roy by taking account their metal ion dependency (4). Meanwhile, PAPS acts as the sulfate donor to numerous nucleophilic acceptors such as steroids and phenols. In such sulfate transfer reactions, S—O fission must occur. PAPS and APS also are known to act as the key intermediates in the reduction of sulfate to sulfite. Here again, the S—O fission may be the most probable mode. 

Metal Ion Effects. The metal ion effects on the acid-catalyzed hydrolysis of PPS also were examined by Benkovic and Hevey (5). However, they observed that in water near pH 3, the rate enhancement in the presence of an excess of metal ion was at most only threefold (Mg2+, Ca2+, Al3+) and in some cases (Zn2+, Co2+, Cu2+) the rate was actually retarded. We thought that the substrate PPS and Mg2+ ion should be hydrated heavily in water so that their complexa-tion for rate enhancement is weak. If, however, the hydrolysis is carried out in a solvent of low water content, such complexation would not occur, and therefore, the rate enhancement might be more pronounced. This possibility appears to be supported by the fact that the active sites of many enzymes are hydrophobic. Of course, there is a possibility that the S—O fission may not require metal ion activation. In this connection, it is interesting to note that in biological phosphoryl-transfer reactions the enzymes generally require divalent metal ions for activity (7, 8, 9), but such metal ion dependency appears to be less important for sulfate-transfer enzymes. For example, many phosphatases require metal ions, but no sulfatase is known to be metal... 

For the understanding of chemistry of sulfate transfer or sulfate reduction in biological systems, we must know the expulsion mechanism of the terminal S03 group of phosphosulfates of adenosine (APS and PAPS). Model studies have disclosed that it can occur by acid catalysis with a mechanism of unimolecular elimination of sulfur trioxide (Figure 3). This acid catalysis can be enhanced by divalent... 

Water-Soluble Annatto Extracts Transfer 2 mL or 2 g of sample into a 50-mL separatory funnel, and add sufficient 2 N sulfuric acid to make the solution acidic to pH test paper (pH 1 to 2). Dissolve the red precipitate of norbixin by mixing the solution with 50 mL of toluene. Discard the water layer, and wash the toluene phase with water until it no longer gives an acid reaction. Remove any undissolved norbixin by centrifugation or filtration, and dry the solution over anhydrous sodium sulfate. Transfer 3 to 5 mL of the dry solution to the top of an alumina column prepared as described above. Elute the column with toluene, three 10-mL volumes of dry acetone, and 5 mL of Carr-Price Reagent (see Solutions and Indicators) added to the top of the column. The orange-red band of norbixin immediately turns blue-green. 

Assay Determine as directed under Solidification Point, Appendix IIB, drying a sample over anhydrous sodium sulfate. Transfer 3 g of the dried oil, accurately weighed, into a test tube, and add 2.1 g of melted o-cresol. The o-cresol must be pure and dry and have a solidification point not below 30°. Insert the thermometer, stir, and warm the tube gently until the mixture is completely melted. Continue as directed in the method. Repeat the procedure until two successive readings agree within 0.10°. Compute the percentage of cineole from the table found under Percentage of Cineole, Appendix VI. Acid Value Determine as directed under Acid Value, Appendix VI. 

Sodium Sulfate Transfer about 1 g of sample, accurately weighed, to a 400-mL beaker, add 10 mL of water, heat the mixture, and stir until completely dissolved. Add 100 mL of alcohol to the hot solution, cover, and digest at a temperature just below the boiling point for 2 h. Filter while hot through... 

Cleland WW, Hengge AC (2006) Enzymatic mechanisms of phosphate and sulfate transfer. 

Baddiley et at. used the reagent to convert adenosine 3, 5 -diphosphate into adenosine 3 -phosphate-5 -sulfatophosphate. In the presence of an appropriate enzyme, this active sulfate transfers the sulfate group to a variety of substrates. 

At least with sulfuric add, key intermediates transfer from and across the interfaces. For example, sec-butyl acid sulfate transfers into the add phase, whereas di -sec-butyl sulfate transfers into and dissolves mainly in the hydrocarbon phase. No information is available on the fraction of isoalkyl fluorides in the two phases. This fraction likely depends on the amount of conjunct polymers in the HF phase. 

Cerebrosides and sphingomyelin are believed to accumulate in the globoid bodies. In fact, the injection of cerebrosides into rats has led to the appearance in the white matter of cells that resemble globoid cells. The biochemical defect in Krabbe s disease is still unknown, but two clues are available. There are no defects in sphingomyelin breakdown, there is a shift in the ratio of cerebrosides to sulfatides (from 3 to 1 in the normal individuals to 12 to 1 in those with leukodystrophy. These observations have led to the suggestion [127-130] that the lipidosis results from a deficiency of a sulfate-transferring enzyme (see Fig. 3-43). 

Figure 21 Free energy of transfer of S04 into ion-selective membranes (a) sulfate transfer into the ionophore-free manbrane is energetically most nnfavorable due to large hydration enragy (b) a nonselective ionophore rednces the phase transfer energy for all ions equally (C) the selective ionophore facilitates sulfate transfer selectively.

Sulfate transfer to flavonoids and glncosinolate precmsors is catalyzed by a small family of soluble sulfotransferases (STs) that use 3 -phos-phoadenosine 5 -phosphosulfate (PzM S) as sulfate donor (Fig. 5). Snlfated flavonols may play a role in the transport of auxins [113], Four position-specific flavonol STs are found in plants of the genus Flaveria, with preferences for the 3-position of the flavonoid aglycone, the 3 and 4 -positions of 3-sulfate derivatives, and the 7-position of 3,3 - or 3,4 -disulfate derivatives [113] (Fig. 5). 

Shioya, T., S. Nishizawa, and N. Teramae, Anion recognition at the liquid-liquid interface. Sulfate transfer across the 1,2-diehloroethane-water interface fadlitated by hydrogen-bonding ionophores, 7 Am Chem Soc, Vol. 120, (1998) p. 11534. 

One aspect of keratan sulfate synthesis that has been investigated at the oeli-frcc level is the process of sulfation. Wortman (1961) demonstrated that incubation of extracts of corneal epithelium, stroma, and endothelium with S-sulfate in the presence of ATP jdelded a radioactive compound with the same electrophoretic mobility as chondroitin sulfate. Keratan sulfate would most likely not have been separated from chondroitin sulfate under the conditions used and could possibly also have been a product of the reaction. In more recent work, Wortman (1963) demonstrated that sulfate transfer could indeed take place to keratan sulfate which was added as acceptor. 

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