Low Concentrations Of Ammonium Sulfate Research Articles

Awaruite, a new large nickel resource: Activation by ammonium sulfate and thiosulfate for flotation

Awaruite is a native nickel-iron alloy with high nickel content and mainly present in serpentinized ultramafic rocks. Recent discoveries have demonstrated the potential for awaruite to contribute to the economics of a nickel deposit. Awaruite selectively floats in weakly acidic conditions with xanthate as collector. However high reagent dosages are required in such conditions since xanthate decomposes and ultramafic rocks are acid consumers. In this work, a novel reagent scheme including ammonium sulfate and sodium thiosulfate is proposed to float awaruite in neutral conditions from ultramafic rocks. Electrochemical studies were carried out on awaruite samples to demonstrate the effect of low concentrations of these reagents on the awaruite surface. The awaruite passivation layer formed in alkaline conditions (natural slurry pH) can, at least, be partially dissolved in the presence of low concentrations of ammonium sulfate and thiosulfate in neutral conditions. After the passivation layer is partially removed, the xanthate collector reacts with the awaruite surface and induces hydrophobicity, thus enabling the awaruite flotation. Microflotation and bench scale flotation tests demonstrate the applicability of the reagent scheme herein proposed. This reagent scheme allows the flotation of awaruite in conditions where xanthate is stable and reduces the acid addition required to adjust the pH.

Solubility of the Sodium and Ammonium Salts of Oxalic Acid in Water with Ammonium Sulfate.

The solubility of the sodium and ammonium salts of oxalic acid in water with ammonium sulfate present has been studied using differential scanning calorimetry, X-ray crystallography, and infrared spectroscopy. The crystals that form from aqueous mixtures of ammonium sulfate/sodium hydrogen oxalate were determined to be sodium hydrogen oxalate monohydrate under low ammonium sulfate conditions and ammonium hydrogen oxalate hemihydrate under high ammonium sulfate conditions. Crystals from aqueous mixtures of ammonium sulfate/sodium oxalate were determined to be ammonium oxalate monohydrate under moderate to high ammonium sulfate concentrations and sodium oxalate under low ammonium sulfate concentrations. It was also found that ammonium sulfate enhances the solubility of the sodium oxalate salts (salting in effect) and decreases the solubility of the ammonium oxalate salts (salting out effect). In addition, a partial phase diagram for the ammonium hydrogen oxalate/water system was determined.

Salting-out as a scalable, in-series purification method of graphene oxides from microsheets to quantum dots

Chemically modified graphenes (CMGs) are used to reinforce composites and as platforms for sensing, electrodes in batteries, conductive films for displays, and others. However, performance of CMG materials is often limited by their physicochemical heterogeneity. Here, we report that simple addition of ammonium sulfate to heterogeneous CMG mixtures, results in effective, scalable, and in-series purification, by salting-out precipitation. The mechanism is based on differences in the dispersibility of the individual graphene oxide (GO). At relatively low ammonium sulfate concentrations (∼10mM), large, GOs with predominant hydrophobic domains are precipitated. As the salt concentration increases, smaller and less GOs with predominant hydrophobic domains are purified, and eventually graphene quantum dots (GQDs) are isolated. The method described herein was inspired by a well-known protein purification process called ‘salting-out,’ in which proteins of different sizes and surface charge, successively become indispersible over a narrow range of salt concentrations. The salting-out process for GOs is simple and scalable, and can be used to achieve large-scale purification.

QCM‐D sensitivity to protein adsorption reversibility

Using a quartz crystal microbalance with dissipative monitoring (QCM-D) we have determined the adsorption reversibility and viscoelastic properties of ribonuclease A adsorbed to hydrophobic self-assembled monolayers. Consistent with previous work with proteins unfolding on hydrophobic surfaces, high protein solution concentrations, reduced adsorption times, and low ammonium sulfate concentrations lead to increased adsorption reversibility. Measured rigidity of the protein layers normalized for adsorbed protein amounts, a quantity we term specific dissipation, correlated with adsorption reversibility of ribonuclease A. These results suggest that specific dissipation may be correlated with changes in structure of adsorbed proteins.

Comparative study on the interaction of recombinant human soluble catechol‐O‐methyltransferase on some hydrophobic adsorbents

The main scope of this work is the evaluation and potential application of hydrophobic interaction chromatography in the isolation of recombinant human soluble catechol-O-methyltransferase (hSCOMT) from an Escherichia coli cell extract. Therefore, a comparative study on the interaction of recombinant hSCOMT with different hydrophobic adsorbents (butyl-, octyl-, phenyl- and epoxy-Sepharose), was developed. The four adsorbents were evaluated in terms of selectivity, recovery and fractionation of recombinant hSCOMT from its Escherichia coli-free culture broth. Our data shows that the adjustment of the ionic strength on the mobile phase and the type of hydrophobic ligand are the most useful factors for a complete binding of hSCOMT and a selective fractionation of contaminating proteins. The results of these studies demonstrate that, although epoxy-Sepharose is used as a last resort due to the high salt concentrations needed, hSCOMT bind to the other three resins at low concentrations of ammonium sulfate (< or = 0.6 M) and eluted just by decreasing the ionic strength on the eluent to 0 M, without loss of specific of activity. The stepwise gradient with 0.6, 0.2, 0.075 and 0 M of ammonium sulfate onto a butyl-Sepharose media was found to be the most effective in the isolation of hSCOMT, leading to an enzyme solution with a 3.9-fold increased in specific activity. Since biochemical and structural studies require significant quantities of the enzyme in an active form, the above described approach may give some insight into the optimization and development of new purification strategies of mammalian COMTs.

Phase diagram of crystallization of Aspergillus niger acid proteinase A, a non-pepsin-type acid proteinase

Proteinase A from Aspergillus niger var. macrosporus is a non-pepsin-type acid proteinase with an extremely low isoelectric point (pI 3.3). The protein is crystallized from ammonium sulfate solutions of pH lower than 4. The crystallization is affected by the presence of dimethylsulfoxide (DMSO). We have studied the phase diagram of the crystallization of proteinase A in the absence and presence of DMSO, to clarify crystallization at such an extremely low pH and to study the effects of DMSO. The results indicate that the logarithm of protein solubility is a rectilinear function of ammonium sulfate concentration in both the absence and presence of DMSO. DMSO definitely lowers the solubility at relatively low concentrations of ammonium sulfate, but had little effect on protein solubility at higher concentrations of ammonium sulfate.

The modulation of cell surface cAMP receptors from Dictyostelium disscoideum by ammonium sulfate

Dictyostelium discoideum cells contain a heterogeneous population of cell surface cAMP receptors with components possessing different affinities ( K d between 15 and 450 nM) and different off-rates of the cAMP-receptor complex ( t 1 2 between 0.7 and 150 s). The association of cAMP to the receptor and the dissociation of the cAMP-receptor complex still occur in the presence of 3.4 M ammonium sulfate. However, these processes are strongly altered. (1) Low concentrations of ammonium sulfate (≈ 50 mM) induce an approx. 2-fold increase of the number of cAMP binding sites. The same effect is induced by millimolar concentrations of CaCl 2. Ammonium sulfate and CaCl 2 are not additive, which suggests that these salts may act via the same mechanism. (2) High concentrations of ammonium sulfate (3.4 M) induce an alteration in the proportioning of the various cAMP binding sites to the components with the highest affinity. (3) High concentrations of ammonium sulfate (3.4 M) retard the dissociation of all binding sites about 3–6-fold, thus giving rise to an increase in the affinity of all cAMP-binding components.

Relative hydrophobicities of Actinomyces viscosus and Actinomyces naeslundii strains and their adsorption to saliva-treated hydroxyapatite.

The present study examined 42 strains of Actinomyces spp. to determine whether adsorption to saliva-treated hydroxyapatite (SHA) of the selected strains of this prominent group of dental-plaque bacteria correlated with hydrophobicity. The relative hydrophobicity of the strains was determined by their adsorption to hydrophobic gels (i.e., phenyl-Sepharose) and their aggregation in ammonium sulfate. Within serogroups the relative hydrophobicity for the strains was similar. The relative adsorption of strains to SHA was also similar within the respective serogroups. Strains which were relatively hydrophobic, as judged by their binding to the hydrophobic gel and aggregation in low concentrations of ammonium sulfate, adsorbed well to SHA. Strains which adsorbed poorly to SHA were relatively hydrophilic since they did not bind well to the hydrophobic gel and were only aggregated in relatively high concentrations of ammonium sulfate. Tween 80, a nonionic detergent known to inhibit hydrophobic interactions, blocked binding of cells to the hydrophobic gel, suggesting that hydrophobic interactions had been inhibited. However, Tween 80 exhibited no influence on the adsorption of cells to SHA. Thus, although there was a strong statistical correlation between the relative hydrophobicity of a strain and its adsorption to SHA, the data were consistent with the view that other interactions, such as ionic bonds and interactions between complimentary macromolecules, are involved in adsorption of the Actinomyces strains to SHA.

A novel thiol-dependent arsenite-sensitive valyl-tRNA synthetase activity from yeast.

Arsenite strongly inhibits the activation by thiols of a fraction of the valyl-tRNA synthetase in yeast extracts that precipitates in low concentrations of ammonium sulfate. Once activated, however, the enzyme is insensitive to arsenite. It is suggested that arsenite blocks the function of an enzyme-bound hydrogen-transferring agent that mediates reduction of the enzyme and normally serves as part of an oxido-reduction regulatory mechanism. On gel filtration, much of the arsenite-sensitive activity behaves as a complex of about 500,000 molecular weight, whereas the behavior of the arsenite-insensitive activity is consonant with the molecular weight of 130,000 previously reported for yeast valyl-tRNA synthetase.

Two deletions within genes for simian virus 40 structural proteins VP2 and VP3 lead to formation of abnormal transcriptional complexes.

The procedure developed by R. M. Fernandez-Muñoz et al. (J. Virol. 29:612-623, 1979) for isolating simian virus 40 (SV 40) chromatin free of disrupted previrions was optimized for preparing late transcriptional complexes, and these complexes were partially characterized. Transcriptional complexes derived from wild-type virus and from several deletion and temperature-sensitive mutants could be activated more than five-fold either by the anionic detergent Sarkosyl or by 300 mM ammonium sulfate, in agreement with the properties of SV40 transcriptional complexes prepared by other procedures. In contrast, complexes from cells infected with deletion mutants dl1261 or dl1262 were not activated at all by a high salt concentration, even though the extent of their activation by Sarkosyl was normal. Mutants dl1261 and dl1262 carry deletions of 54 and 36 base pairs, respectively, at an approximate map position of 0.91, which is within the overlapping genes for the virion proteins VP2 and VP3. The effects of these deletions on transcription in vitro indicate that VP2 or VP3 or both are bound to late transcriptional complexes in a way that affects the progress of initiated RNA polymerase. The properties of late transcriptional complexes derived from wild-type SV40 can be explained by the presence of the following two different kinds of complexes: (i) a minority class (about 20%), which is free of VP2 or VP3, active at low concentrations of ammonium sulfate in vitro, and responsible for late transcription in vivo, and (ii) a majority class (about 80%) with VP2 or VP3 bound, which is inactive at low salt concentrations both in vitro and in vivo but capable of being activated by high salt concentrations or by Sarkosyl. We propose that mutant VP2 and VP3 proteins from dl1261 and dl1262 bind to the majority class of late transcriptional complexes in a way that can be reversed by Sarkosyl but not by a high salt concentration.

Separation of transfer ribonucleic acid by sepharose chromatography using reverse salt gradients.

The transfer ribonucleic acids of Escherichia coli bind to unsubstituted Sepharose in the presence of high concentrations of ammonium sulfate at pH 4.5. Transfer RNA species are eluted individually from the Sepharose by a gradient from high to low concentrations of ammonium sulfate; leucine tRNA is fractionated into five isoaccepting species. The order of elution of these isoaccepting species differs from that seen with reverse phase chromatography. By means of only these two procedures, one isoaccepting species of leucine tRNA can be purified to apparent homogeneity. Isoaccepting tRNA species for 9 amino acids have been resolved. This established the general utility of this chromatographic system for the separation and purification of specific isoaccepting transfer RNAs.

Pre-ribosomal RNA synthesis in isolated rat-liver nucleoli.

Isolated rat liver nucleoli represent a simple system to study transcription and processing of ribosomal RNA in vitro. These organelles retain their ability to synthesize ribosomal precursor RNA in vitro as measured by the incorporation of nucleotides into RNA. The incorporation of labelled nucleotides is not affected by α‐amanitin or rifampicin AF‐013. Low concentrations of ammonium sulfate (60 mM) stimulate the nucleolar synthetic activity considerably. The (A + U)/(G + C) ratio of nucleolar RNA synthesized in vitro is 0.5–0.55 and resembles that of ribosomal precursor RNA. Discrete peaks of high‐molecular‐weight RNA, widely distributed as to size, appear in analytical sucrose gradients. Molecules with sedimentation coefficients up to about 80 S have been obtained a surprising result in view of the fact that, in general, only 45‐S precursors are found in vivo. The amount of rapidly sedimenting RNA increases with prolonged incubation. It is uncertain whether or not the presence of ribosomal RNA precursor molecules with sedimentation coefficients greater than 45‐S reflects a normal transcription mechanism in the living cell which remains undetected due to rapid processing. It is also possible that isolated nucleoli may have lost some specific factors which in vivo cause the RNA polymerase to terminate the RNA chains at the end of the 45‐S transcription unit.

Unusual, Metabolite-dependent Solubility Properties of Phosphofructokinase: THE BASIS FOR A NEW AND RAPID PURIFICATION FROM LIVER, KIDNEY, AND OTHER TISSUES

Abstract In the presence of 5 mm MgCl2, fructose 6-phosphate kinases from porcine liver and kidney and a variety of other sources: (a) precipitate at low ammonium sulfate concentrations (0 to 30 mm); (b) are completely soluble at slightly higher concentrations (g100 mm); and (c) do not precipitate at low (0 to 30 mm) ammonium sulfate concentrations if fructose-6-P is present or if Mg2+ is absent and 1 mm ATP is present. Although substrate effects on enzymes are well known, the precipitation-solubilization effects just described are, in many respects, novel. These properties also form the basis for a new, rapid and highly specific method for complete purification of porcine liver and kidney phosphofructokinases, as well as substantial purification of other phosphofructokinases. Porcine liver phosphofructokinase was purified 16,000-fold to homogeneity (specific activity = 100) with a 25% yield in only 8 hours. No conventional salt fractionation or column chromatography is required. The key step is repeated selective precipitation and dissolution of the enzyme by simply changing the concentration of ammonium sulfate in the solution. In contrast to conventional ammonium sulfate fractionation, the enzyme is precipitated and dissolved at lower and higher ionic strengths, respectively. The enzyme has a low isoelectric point (pI = 5). Metaboliteinduced structural transitions are also detectable by polyacrylamide gel electrophoresis. In the absence of metabolites, the enzyme does not penetrate 4.2% polyacrylamide gels but in the presence of fructose-6-P or ATP or ADP, it does.

Enzyme activity in cryobiological systems: III. Low-temperature properties of honeybee glyceraldehydephosphate dehydrogenase

Certain properties of honeybee and rabbit muscle GPDHs have been examined in vitro. While incubation of rabbit muscle GPDH at 0 °C in the presence of 4 m m ATP results in its dissociation, the enzyme from honeybees retains its native tetrameric structure. Furthermore all adenine nucleotides tested caused some inactivation of rabbit muscle GPDH but had either only a slight effect or none at all on the honeybee enzyme. However, both enzymes are competitively inhibited by ATP, ADP, and AMP and 3′,5′-AMP. In the absence of ammonium sulfate and ATP, honeybee GPDH was partially inactivated at 0 °C while the rabbit muscle enzyme was not affected. Inactivation of honeybee GPDH could be presented by low concentrations of ammonium sulfate. The honeybee enzyme retains essentially full activity over the pH range 6.5–8.0 when incubated with 10 m m ATP at 0 °C, while the rabbit muscle enzyme has been shown to be completely inactivated over this pH range in the presence of 2 m m ATP at 0 °C. On the basis of studies with adenine nucleotides it is concluded that insect GPDHs probably have evolved a capability for catalytic function at low temperature while retaining the ability to have this function controlled by these compounds.

Transport of Sugars and Amino Acids in Bacteria: III. Studies on the Restoration of Active Transport

Abstract Shocked cells have been examined with respect to their sensitivity to inhibitors of active transport. They behave similarly to unshocked cells except that their transport ability is reduced. The process of restoration of active transport has been studied. Metabolic energy appears to be necessary to restore the uptake ability of shocked cells. Evidence is presented which suggests that the galactose- and leucine-binding proteins can become reassociated with the shocked cells. The process shows saturation kinetics and results in an increase in transport ability. We speculate that there are specific sites capable of interacting with the binding proteins. In addition to binding protein, another nondialyzable factor in shock fluid is found to be active in restoration of transport. This factor is precipitated by low concentrations of ammonium sulfate and does not have binding properties. Its activity is substantial and restoration of transport to nearly the original level can be shown only when this factor is used in combination with binding protein.

Enzyme systems in the mycobacteria: VI. Further studies on the pyruvic dehydrogenase system

1. 1. The pyruvic dehydrogenase complex of the H37Ra strain of Mycobacterium tuberculosis var. hominis has been resolved into two fractions. 2. 2. The first fraction, precipitating at high ammonium sulfate concentrations, contains a lipoic dehydrogenase. This enzyme catalyzes the oxidation of lip(SH) 2 by DPN; the reverse reaction has not been demonstrated. The lipoic dehydrogenase has been purified at least twenty-fold over the crude cell-free extract. DL-α-lipoamide is reduced by DPNH and the lipoicc dehydrogenase. E 0′ for the lip(SH) 2 ⤥ lipS 2 couple at 22° and pH 6.0 was shown to be —0.23 V. 3. 3. The second fraction, precipitating at low ammonium sulfate concentrations, contains, in addition to the pyvuric dehydrogenase, a lipoic transacetylase. This enzyme catalyzes the reversible transfer of an acetyl group from acetyl CoA to lip(SH) 2. The enzyme has been purified at least fifteen-fold over the crude cell-free extract. 4. 4. Associated with the pyruvic dehydrogenase-lipoic transacetylase complex is a lipoic deacylase which hydrolytically cleaves S-acetyl-lip(SH) to acetate and lip(SH) 2. 5. 5. The possible existence of a soluble pyruvic dehydrogenase complex of enzymes in cell-free extracts of H37Ra and the presence of another form of lipoic acid are discussed.