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PubMed1984

Effects of fixing and staining on images of tropomyosin Mg-paracrystals.

Tropomyosin Mg-paracrystals have been studied by positive and negative staining with uranyl acetate and sodium phosphotungstate, either unfixed or fixed with glutaraldehyde. Fixation causes changes in some of the paracrystal bands. Some of the bands are more intense when a positively-charged staining ion is used than when a negatively-charged ion is used, in both negative and positive-staining techniques. This result rules out the suggestion that negative staining is not affected by the charge of the stain in tropomyosin, and agrees with findings in other specimens. Therefore it is unlikely that any simple parameter based on residue size can be used to predict the image intensity from the amino acid sequence for tropomyosin. These staining patterns cast doubt on the earlier interpretation of a prominent white band in the paracrystal as an overlap of alpha-helical molecular ends.

Animals↗
PubMed2005

Potentiometric flow injection analysis of mebeverine hydrochloride in serum and urine.

Four PVC membrane electrodes for the determination of mebeverine hydrochloride (MvCl) were fabricated and fully characterized in terms of composition, life span, usable pH range, working concentration range and temperature. The membranes of these electrodes consist of mebeverinium-silicotungstate (Mv-ST), silicomolybdate (Mv-SM), phosphotungstate (Mv-PT), or phosphomolybdate (Mv-PM) ion-associations dispersed in PVC matrix with dibutyl phthalate plasticizer. The electrodes showed near-Nernstian response over the concentration range of 4.0 x 10(-6) to 1.0 x 10(-2)M MvCl and were applied to the potentiometric determination of mebeverinium ion in pharmaceutical preparations, serum and urine in steady state and flow injection (FI) conditions with average recoveries of 96.4-102 % and relative standard deviations of 0.132-1.86%. The electrodes exhibit good selectivity for MvCl with respect to a large number of inorganic cations, organic cations, sugars and amino acids. The sensitivities of these electrodes are high enough to measure as low as 1.86 microg/ml of MvCl which permit the determination of the Ksp values of the ion-associates used. The proposed potentiometric methods offer the advantages of simplicity, accuracy, automation feasibility and applicability to turbid and colored sample solutions.

Flow Injection Analysis↗
PubMed1979

The ultrastructure of the major species of an enriched methanogenic culture utilizing acetic acid.

The ultrastructure of the cells of the major component of an enriched culture of a presumed methanogen which utilized acetic acid was studied by transmission and scanning electron microscopy. The filaments were composed of Gram-positive, rod-shaped cells, 1--2 micrometer in length and about 0.5 micrometer in breadth, attached end to end. Septa between cells were complex, with a central, electron-dense sheet which had a spherical enlargement in the center separating the cell walls. The cells walls themselves were of variable thickness with a light, fluffy, thin portion on the outside and a denser, thicker portion within. They contain a series of rings stacked side by side which are composed of material that stains strongly and positively with phosphotungstate ion. The cytoplasmic membrane of these cells had an outer leaflet which stains more densely with uranium and lead ions than the inner leaflet. There were no recognizable organelles in the cytoplasm other than ribosomes. It is shown in these observations that the presumed methanogen may likely be a new species.

Acetates↗
PubMed2005

New conventional coated-wire ion-selective electrodes for flow-injection potentiometric determination of chlordiazepoxide.

New chlordiazepoxide hydrochloride (Ch-Cl) ion-selective electrodes (conventional type) based on ion associates, chlordiazepoxidium-phosphomolybdate (I) and chlordiazepoxidium-phosphotungstate (II), were prepared. The electrodes exhibited mean slopes of calibration graphs of 59.4 mV and 60.8 mV per decade of (Ch-Cl) concentration at 25 degrees C for electrodes (I) and (II), respectively. Both electrodes could be used within the concentration range 3.16 x 10(-6)-1 x 10(-2) M (Ch-Cl) within the pH range 2.0-4.5. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficients of the electrodes, which were 0.00139 and 0.00093 V degrees C(-1) for electrodes (I) and (II), respectively. The electrodes showed a very good selectivity for Ch-Cl with respect to the number of inorganic cations, amino acids and sugars. The electrodes were applied to the potentiometric determination of the chlordiazepoxide ion and its pharmaceutical preparation under batch and flow injection conditions. Also, chlordiazepoxide was determined by conductimetric titrations. Graphite, copper and silver coated wires were prepared and characterized as sensors for the drug under investigation.

Calibration↗
PubMed1978

Biochemical and morphological characterization of mycobacteriophage R1.

Large-scale propagation of mycobacteriophage R1 in broth culture has allowed the isolation of quantities of virus sufficient for characterization of its nucleic acid and lipid components as well as investigation of its ultrastructural attributes. Analysis of R1 DNA indicates that it is double stranded and possesses a molecular weight of 2.5 X 10(7) and a guanine-plus-cytosine content of 65.7 +/- 0.5%. The lipid fraction of R1 accounts for 14% of the total dry weight of the virus, 20% of which was identified as free or esterified sterols. A rapid loss of viral titer occurred after seconds of exposure to organic solvents. This result suggests that the lipid fractions of R1 is essential for its infectivity. Electron microscopic investigation of solvent-extracted R1 showed extensive deterioration of its normal morphology, including nucleocapsid disintegration and base plate separation. Routine phosphotungstate preparations demonstrated a particle with an oval head and a noncontractile tail. Altering the pH of the phosphotungstate negative stain from neutrality damage the viral particles. Uranyl formate-contrasted specimens displayed an elongated hexagonal nucleocapsid with a neck region; the cross-striated tail possessed a starlike base plate.

Cytosine↗
PubMed2005

Ion-selective electrodes for potentiometric determination of ranitidine hydrochloride, applying batch and flow injection analysis techniques.

New ranitidine hydrochloride (RaCl)-selective electrodes of the conventional polymer membrane type are described. They are based on incorporation of ranitidine-tetraphenylborate (Ra-TPB) ion-pair or ranitidine-phosphotungstate (RaPT) ion-associate in a poly(vinyl chloride) (PVC) membrane plasticized with dioctylphthalate (DOP) or dibutylphthalate (DBP). The electrodes are fully characterized in terms of the membrane composition, solution temperature, and pH. The sensors showed fast and stable responses. Nernstian response was found over the concentration range of 2.0 x 10(-5) M to 1.0 x 10(-2) M and 1.0 x 10(-5) M to 1.0 x 10(-2) M in the case of Ra-TPB electrode and over the range of 1.03 x 10(-5) M to 1.00 x 10(-2) M and 1.0 x 10(-5) M to 1.0 x 10(-2) M in the case of Ra-PT electrode for batch and FIA systems, respectively. The electrodes exhibit good selectivity for RaCl with respect to a large number of common ions, sugars, amino acids, and components other than ranitidine hydrochloride of the investigated mixed drugs. The electrodes have been applied to the potentiometric determination of RaCl in pure solutions and in pharmaceutical preparations under batch and flow injection conditions with a lower detection limit of 1.26 x 10(-5) M and 5.62 x 10(-6) M at 25 +/- 1 degrees C. An average recovery of 100.91% and 100.42% with a relative standard deviation of 0.72% and 0.53% has been achieved.

Journal Article↗
PubMed1975

Studies on chromatin. IV. Evidence for a toroidal shape of chromatin subunits.

Electron microscopy of purified chromatin subunits (v-bodies [17] or nucleosomes [2] revealed a hole or at least a deep indentation in the globular nucleosome. A hole in the nucleosome was visualized using rotatory shadowing with platinum-palladium or more directly, by negative staining with sodium phosphotungstate. The diameter of the hole as measured from negatively stained samples is 10-25 A. The external diameter of the negatively stained nucleosome equals 75 +/- 15 A. Although most of the data are formally compatible with either a hole or a deep indentation in the nucleosome, some views of the particles in the negatively stained samples suggest a hole rather than an indentation. The possible significance of a toroidal structure of the chromatin subunit is discussed in the accompanying paper [3].

Animals↗
PubMed2005

PVC membrane ion-selective electrodes for the determination of Hyoscyamine in pure solution and in pharmaceutical preparations under batch and flow modes.

New PVC membrane electrodes selective for the determination of hyoscyamine ion (Hy(+)) based on hyoscyamine tetraphenylborate (Hy-TPB) or hyoscyamine phosphotungstate (Hy-PT) ion-exchangers as electroactive materials are described. The electrodes show a linear response for Hy(+) over the concentration range of 1.00 x 10(-5) to 1.26 x 10(-2) mol L(-1) and 1.00 x 10(-4) to 1.00 x 10(-2) mol L(-1) in case of Hy-TPB electrode applying batch and flow injection analysis (FIA), respectively, and 1.00 x 10(-5) to 4.52 x 10(-3) mol L(-1) and 6.31 x 10(-5) to 1.00 x 10(-2) mol L(-1) in case of Hy-PT electrode for batch and FIA, respectively. The lower detection limits are 3.90 x 10(-6) and 4.51 x 10(-6) at 25 degrees C for Hy-TPB and Hy-PT electrodes, respectively. The electrodes posses near Nernstian slopes of 56.5 and 57.8 mV/decade for Hy-TPB and Hy-PT electrodes, respectively, and a fast potential response of < or =20 s which is almost constant over a pH range of 3-10. Selectivity coefficient data for some common inorganic cations, sugars, amino acids and the components, other than hyoscyamine, of the mixed drugs investigated show negligible interference. The electrodes have been applied to the potentiometric determination of hyoscyamine in pure solution and in pharmaceutical preparations under batch and FIA conditions and as end point indicator electrode for the determination of hyoscyanine using potentiometric titration. For the concentrations (1.08 x 10(-5) mol L(-1) to 3.16 x 10(-3) mol L(-1)) an average recovery of 99.95% with relative standard deviation of 0.63% has been achieved. The effect of temperature on the electrodes was also studied.

Atropine↗
PubMedDate not supplied

Evidence for amelogenin "nanospheres" as functional components of secretory-stage enamel matrix.

Amelogenins are the principal proteins of the extracellular matrix of developing dental enamel and are postulated to function in the processes of biomineralization of the developing tooth although the molecular mechanisms concerned are poorly understood. Recent imaging studies, employing dynamic light scattering, atomic force, and transmission electron microscopy (TEM) have shown that a recombinant amelogenin (M(r) approximately 20,000 Da) spontaneously forms supramolecular quasi-spherical aggregates ("nanospheres") of 15-20 nm in diameter. By comparison with in vitro experiments employing the recombinant amelogenin we show that the nanospheres appear as electron-lucent structures when treated with conventional electron microscopy contrast reagents (phosphotungstate or uranyl acetate) and we speculate that this property derives from the hydrophobic nature of the amelogenin protein. Employing TEM preparations of developing enamel from mouse, bovine, and hamster we demonstrate that the amelogenin nanospheres occur as beaded rows of electron-lucent structures aligned with, and separating, the enamel mineral crystallites. We postulate that the amelogenin monomers self-assemble to form nanospheres which function to space the initial crystallites, control crystal habit, inhibit intercrystalline fusions, and, through the apposition of their surfaces, create anionic channels which facilitate ion transport within the mineralizing matrix.

Amelogenesis↗
PubMed1983

Isolation and characterization of lipoprotein lipase activators from bovine blood serum.

Bovine serum lipoproteins were fractionated into high density and low and very low density lipoproteins by precipitation with sodium phosphotungstate and magnesium chloride. From each lipoprotein fraction seven apo C peptides were isolated by gel filtration and ion exchange chromatography. The two lipoprotein fractions probably contain identical apo C peptides but in different proportions. Two of the apo C peptides activated lipoprotein lipase from milk in vitro. Their specific activities were about 2000 times as high as that of the original serum. The apo C fraction from low-very low density lipoproteins had a specific activity three times that from high density lipoproteins. Also, the activator peptides from low and very low density lipoproteins gave one band on alkaline urea gel electrophoresis whereas corresponding peptides from high density lipoproteins were slightly heterogeneous. The low and very low density lipoproteins, therefore, seem to be the fraction of choice for isolation of activators for lipoprotein lipase.

Amino Acids↗
PubMed2006

Effects of exogenous collagenase and cholesterol esterase on the durability of the resin-dentin bond.

PURPOSE: The purpose of this work was to determine microtensile dentin bond strengths (microTBS) of dentin-resin composite bonds after three-month storage in artificial saliva containing either collagenase (COL) or cholesterol esterase (EST). The null hypothesis tested is that the resin-dentin bond strength is equivalent for each storage medium at the tested storage times. MATERIALS AND METHODS: Resin composite was bonded to occlusal dentin, and microTBS specimens were formed and stored in the artificial saliva, COL, EST, or synthetic oil. After 24 h and 12-week storage, microTBS was determined and failure modes were characterized by SEM. The interfacial ultrastructure was evaluated by transmission electron microscopy as unstained and stained sections (phosphotungstic acid/uranyl acetate). Statistical analysis was performed by ANOVA and Weibull survival analyses at the 0.05 level of statistical significance. RESULTS: There were significantly weaker bond strengths after 12 weeks for all experimental storage media (p < 0.001). Artificial saliva containing EST lowered bond strengths to a significantly greater extent than did COL after 12 weeks of storage, while no difference between these groups could be discerned after 24 h. Therefore, the null hypothesis of this experiment is rejected. CONCLUSION: Exogenous enzymatic challenge to resin-dentin bonds decreased bond durability only with EST. However, when further challenges to ideal infiltration of the comonomers into the hybrid layer were carried out using inadequate removal of solvent, additional alterations in hybrid layer ultrastructure were discerned by TEM that may represent different potential degradative processes. The contribution of endogenous enzymatic challenges to the primary degradative process, ie, hydrolysis, is unknown and deserves continued attention.

Acid Etching, Dental↗
PubMed1994

Domain structure of the Acetogenium kivui surface layer revealed by electron crystallography and sequence analysis.

The three-dimensional structure of the Acetogenium kivui surface layer (S-layer) has been determined to a resolution of 1.7 nm by electron crystallographic techniques. Two independent reconstructions were made from layers negatively stained with uranyl acetate and Na-phosphotungstate. The S-layer has p6 symmetry with a center-to-center spacing of approximately 19 nm. Within the layer, six monomers combine to form a ring-shaped core surrounded by a fenestrated rim and six spokes that point towards the axis of threefold symmetry and provide lateral connectivity to other hexamers in the layer. The structure of the A. kivui S-layer protein is very similar to that of the Bacillus brevis middle wall protein, with which it shares an N-terminal domain of homology. This domain is found in several other extracellular proteins, including the S-layer proteins from Bacillus sphaericus and Thermus thermophilus, Omp alpha from Thermotoga maritima, an alkaline cellulase from Bacillus strain KSM-635, and xylanases from Clostridium thermocellum and Thermoanaerobacter saccharolyticum, and may serve to anchor these proteins to the peptidoglycan. To our knowledge, this is the first example of a domain conserved in several S-layer proteins.

Amino Acid Sequence↗
PubMed2002

Structural basis for inhibition of protein tyrosine phosphatases by Keggin compounds phosphomolybdate and phosphotungstate.

Protein-tyrosine phosphatases (PTPs) constitute a family of receptor-like, and cytoplasmic enzymes, which catalyze the dephosphorylation of phosphotyrosine residues in a variety of receptors and signaling molecules. Together with protein tyrosine kinases (PTKs), PTPs are critically involved in regulating many cellular signaling processes. In this study, diverse compounds were screened for PTP inhibition and selectively screened for inhibitors with the end product inhibition properties. Among phosphate analogues and their derivatives for PTP inhibition, Keggin compounds phosphomolybdate (PM) and phosphotungstate (PT) strongly inhibited both PTP-1B and SHP-1, with K(i) values of 0.06-1.2 micromM in the presence of EDTA. Unlike the vanadium compounds, inhibition potencies of PM and PT were not significantly affected by EDTA. PM and PT were potent, competitive inhibitors for PTPs, but relatively poor inhibitors of Ser/Thr phosphatase. Interestingly, PM and PT did not inhibit alkaline phosphatase at all. The crystal structure of PTP-1B in complex with PM, at 2.0 A resolution, reveals that MoO(3), derived from PM by hydrolysis, binds at the active site. The molybdenium atom of the inhibitor is coordinated with six ligands: three oxo-ligands, two apical water molecules and a S atom of the catalytic cysteine residue. In support of the crystallographic finding, we observed that molybdenium oxides (MoO(3), MoO(2), and MoO(2)Cl(2)) inhibited PTP-1B with IC(50) in the range 5-15 micromM.

Binding, Competitive↗