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At least 505 records · Page 28Linked to original sources
PubMed2002

Fluoride concentrations in thoroughbred horses in India.

Fluoride possesses both essential and toxic potentials. A cross-sectional study recorded the fluoride concentrations in sera of thoroughbred horses 5y of age from 4 localities in India. A total of 628 serum samples of were analyzed for fluoride content using ion selective potentiometry. The mean serum fluoride was estimated as 0.018 +/- 0.002, 0.096 +/- 0.004, 0.16 +/- 0.008 and 0.32 +/- 0.02 ppm in horses from the eastern, central. western and southern parts of the country respectively. Although there were significant difference in fluoride concentration among horses from different zones, all werewithin the normal range for this species.

Animals↗
PubMedDate not supplied

[Direct determination or estimated value of plasma ionized calcium : indications and limits].

Calcium plays a fundamental role in many essential for life functions. Ionized calcium (Ca(++) ) represents free fraction and 50% of the total calcium in the plasma is accepted as its physiologically active form. On almost all laboratories, only total calcium is routinely measured, and ionized calcium concentration is calculated based on calcium, protein or albumin concentrations for many plasma sample or with others parameters like pH. Since 1935, the literature was abounted with "correction" formulae of varying degree of sophistication. Many laboratories routinely use correction formulae to either calculate an "adjusted" or "corrected" total calcium, or "ionized" fraction is calculated,but these determinations lack of accuracy or precision. Errors associated with the measurement of the other variables contribuate to the difficulty in producing a useful correction formulae. Direct measurement of ionized calcium by potentiometry is the method of choice for this assay. Improvements in ion selective electrodes (ISE) technology make possible the routine clinical measurement of Ca(++). However this technology implies several obligations for its use, particulary in blood ampling, storage and transport. In this review, characteristics of different available analysers are described. We think that Ca(++) should be systematically performed and not calculated in pathological situations where an possible alteration of the calcium metabolism is found especially in multiple myeloma in which paraprotein may bind calcium.

Blood Chemical Analysis↗
PubMed1992

[Calcium metabolism in various forms of hypertrophy of the "hypertensive" heart].

To study the changes occurred in integral calcium metabolic parameters in evolving "hypertensive" heart, a total of 100 patients with Stage I-II (WHO Classification) were examined. Myocardial structure and function were echocardiographically examined. Plasma concentrations of ionized calcium were measured by direct potentiometry. Plasma levels of calcitonin and parathyroid hormone were measured by radioimmunoassay. As the "hypertensive" heart progressed, the ionization of serum calcium was found to enhance along with an increase in calcitoninemia. In early formation of the "hypertensive" heart, parathyroid hormone remained unchanged, but became elevated only in severe left ventricular hypertrophy. The findings may explain the features of the clinical aspects of variant left ventricular hypertrophies in the "hypertensive" heart.

Calcitonin↗
PubMed1992

[Construction and application of all-solid-state aconitine electrochemical detector in flow injection analysis].

A new kind of all-solid-state electrochemical detector for very toxic alkaloids such as aconitine, mesaconitine and hypaconitine has been studied. It exhibits Nernstian response for these alkaloids with a slope of 56 mV/decade over the concentration range of 3 x 10(-5)-1 x 10(-2) mol/L at pH 2-7 under the flow condition. Direct potentiometry for the determination of aconitine in Aconitum kusnezoffii Reichb., Aconitum carmichaeli Debx. and Xiaohuoluo Wan showed average recoveries of 98.5, 98.3 and 96.8% and relative standard deviations of 1.8, 2.4 and 3.5%, respectively. It can be used for the determination of very toxic alkaloids in the above mentioned samples by flow injection analysis. It also can be used for the study of the hydrolytic kinetics of aconitine.

Aconitine↗
PubMed2003

Some physicochemical properties of 4-amino-3,5-dinitrobenzoic acid (ADBA).

Some physicochemical properties of the aromatic amino acid 4-amino-3,5-dinitrobenzoic acid (ADBA) were determined. This provides, for the first time, quantitative data about this chemical of current pharmaceutical and biomedical interest. The analytical reagent grade of ADBA has 100% purity, determined by potentiometry. The ionization constant (pKa) is 4.00 +/- 0.04. The specific absorbance of ADBA [A(1%, 1 cm)] was determined as 389.42 +/- 51.33 and 381.67 +/- 38.99 (p = 0.05) in water (435 nm) and octanol (415 nm), respectively. The lipophilicity of ADBA is described by its octanol/water partition coefficient (Log P) of -1.50. An analogous parameter descriptive of lipophilicity, the chromatographic hydrophobicity index (Rm), was determined as -0.84 on reversed phase thin layer chromatography (RPTLC). ADBA is more acidic thanp-amino benzoic acid (PABA), the prototype aromatic amino acid of which ADBA is an analogue. It is also about thirty-two times more water soluble than in n-octanol. These findings have a predictive value with respect to absorption and distribution of this compound in living organisms.

Chemical Phenomena↗
PubMed2003

[Evaluation of toxic doses of fluorine on expression of collagen genes and synthesis of some collagen proteins in rat skin].

The results of studies carried out over the last few decades indicate a significant involvement of fluoride in connective tissue metabolism. Unfortunately, opinions concerning this issue vary and sometimes are conflicting. Collagen constitutes the main component of the extracellular matrix. Biosynthesis of collagen is a complex, multistage process. Each step in collagen biosynthesis may be affected by exogenous factors. The purpose of the present study was to evaluate the effects of toxic doses of fluoride in drinking water on: 1. The level of COL1A1 gene expression in rat skin; 2. Concentrations of acid-soluble, pepsin-soluble and total collagen isolated from rat skin; 3. Ratio of pepsin-soluble to acid-soluble collagen concentrations; 4. Proportions of alpha2(I)/alpha1(I) and beta/alpha1(I) collagen chains in extracts ofpepsin-soluble collagen. An attempt was made to determine whether fluoride effects are gender-dependent. The experiment was performed in 108 Wistar rats (males and females). Rats were given 60 mg sodium fluoride/dm3 in drinking during 1, 3 or 6 months. Subsequently, animals were sacrificed and blood, femoral bones and fragments of abdominal skin were taken for analysis. Methods used in the study included potentiometry with F- ion-selective electrode, RT-PCR assay, calorimetry, and SDS-PAGE electrophoresis. The results led to the following conclusions: 1. COL1A1 gene expression in the skin of male rats receiving 60 mg NaF/dm3 in drinking water was significantly reduced after 6 months exposure. 2. Fluoride at doses used in the present study basically does not exert an effect on the concentration of each collagen form in rat skin, ratio of pepsin-soluble to acid-soluble collagen concentrations, and relative proportions of some collagen chains in the pepsin-soluble collagen extract. 3. Male rats were more sensitive to fluoride action in the present study as compared with females. 4. Further research on fluoride penetration to the skin in experimental animals is needed in order to elucidate the relatively low toxicity of fluoride in this tissue.

Administration, Oral↗
PubMed1991

Functional expression of NADPH oxidase components (alpha- and beta-subunits of cytochrome b558 and 45-kDa flavoprotein) by intrinsic human glomerular mesangial cells.

Recently, we have shown that human glomerular mesangial cells (HMCs) release oxygen radicals from the plasma membrane in response to cytokines. Now we have used diphenylene iodonium, a covalent binding inhibitor of activated 45-kDa flavoprotein, in neutrophils radiolabeled with 125I and could identify a 45-kDa protein band in a separated HMC plasma membrane fraction. Low temperature difference spectroscopy showed a peak absorbance at 428 and 558 nm. Direct potentiometry of HMC membranes (-340 to -160 mV) showed the presence of a low potential cytochrome (76 pmol/mg to HMC membrane protein) identified as cytochrome b558. In slot blots, mouse monoclonal antibody (mAb) 7D5, specific for the extracellular domain of the alpha-subunit, showed a positive reaction with HMCs. In Western blots, mAb 449, directed against the cytoplasmic epitope of the alpha-subunit, identified a 23-kDa protein; and mAb 48, raised against the large (beta) subunit of cytochrome b558 of human neutrophils (Verhoeven, A. J., Bolscher, B. G. J. M., Meerhof, L. J., van Zwieten, R., Keijer, J., Weening, R. S., and Roos, D. (1989) Blood 73, 1686-1694), detected a smear between 75 and 100 kDa in denatured HMC membrane protein. These data determined with HMCs, suggest for the first time the expression of three essential components of NADPH:O2- oxidoreductase in mesenchymal cells.

Antibodies, Monoclonal↗
PubMed2005

[Dependence of rifabutin properties and liposome entrapment on pH of the medium].

Rifabutin solubility within pH 3.0 to 11.0 was determined. Potentiometry, spectrophotometry and computation revealed ionization of three groups with pKa 3.5, 6.5 and 9.5 in the rifabutin molecule. On the basis of the pKa values of certain fragments of the rifabutin molecule computed by the ACD/pKa programme they were related to ionization of the following groups: imidazole residue nitrogen, aromatic hydoxyl and piperidin nitrogen respectively. Interaction of rifabutin with model membranes, i. e. large unilamellar vesicules was studied. At lower pH of the medium, entrapment of rifabutin to the large unilamellar vesicules increased that was evident of satisfactory correlation with the decrease in the rifabutin distribution coefficient in the system multilamellar vesicules/water under the experimental conditions.

Antitubercular Agents↗
PubMed2006

Sequence-specific Ni(II)-dependent peptide bond hydrolysis in a peptide containing threonine and histidine residues.

Previously we demonstrated that Ni(II) complexes of Ac-Thr-Glu-Ser-His-His-Lys-NH2 hexapeptide, representing residues 120-125 of human histone H2A, and some of its analogs undergo E-S peptide bond hydrolysis. In this work we demonstrate a similar coordination and reactivity pattern in Ni(II) complexes of Ac-Thr-Glu-Thr-His-His-Lys-NH2, its threonine analogue, studied using potentiometry, electronic absorption spectroscopy and HPLC. For the first time we present the detailed temperature and pH dependence of such Ni(II)-dependent hydrolysis reactions. The temperature dependence of the rate of hydrolysis yielded activation energy E(a) = 92.0 kJ mol(-1) and activation entropy DeltaS# = 208 J mol(-1) K(-1). The pH profile of the reaction rate coincided with the formation of the four-nitrogen square-planar Ni(II) complex of Ac-Thr-Glu-Thr-His-His-Lys-NH2. These results expand the range of protein sequences susceptible to Ni(II) dependent cleavage by those containing threonine residues and permit predictions of the course of this reaction at various temperatures and pH values.

Amino Acid Sequence↗
PubMed1990

Electrode measurement of glucose and urea in undiluted samples.

The development of ion-selective electrodes (ISEs) for electrolyte measurements necessitates a re-evaluation of the biological and clinical interpretation of a result. In pathological situations (e.g., hyperlipidemia and hyperproteinemia) direct potentiometry is the method of choice for ion measurements in blood. However, the "plasma water effect" exists also in normal samples, requiring new reference values for physiological ranges. A compromise between medical and instrumentation workers retained the old reference values (flame photometry for Na+ and K+) by introducing correction factors into the ISE instruments, so that the results for direct ISE and flame photometry are the same for "normal" samples. Analyses of "abnormal" samples will reveal biases between the two methods. Now, a new generation of electrodes for assaying additional metabolites reopens the issue. Although classical methods measure a quantity of substance in a predetermined volume of sample, the majority of the substance is usually in the aqueous phase, and the volumes occupied by lipid and protein are not taken into consideration. In evaluating the NOVA 12 instrument (NOVA Biomedical), using electrodes for direct measurement in serum or plasma of Na, K, Cl, total CO2, urea, and glucose, we have demonstrated the inadequacy of classical measurements of urea and glucose, especially in pathological situations characterized by a large variation in the plasma water fraction.

Analysis of Variance↗
PubMed1979

Secondary structure in very low density and intermediate density lipoproteins of human serum.

We have studies the secondary structures of the protein moieties of very low density lipoproteins (VLDL) and intermediate density lipoproteins (IDL) of human serum by circular dichroism (CD). Two potential complications in the application of this technique to lipoproteins have been evaluated. First, using chronographic potentiometry in CD measurements of VLDL fractions of different mean particle diameters, we have analyzed statistically the CD signals in order to define the limits imposed by light scattering with respect to both particle diameter and wavelength. We found that CD measurements can be made to as low as 210 nm on particles of 520 A or smaller, and to 194 nm on particles of 450 A and below. Second, we have evaluated the CD contribution of lipid chromophores. Despite the high ratio of lipid to protein, the relative CD effect of the lipids is smaller than for low density lipoproteins (LDL). due to the extremely small ellipticity of natural VLDL triglycerides. Thus, CD measurements can be obtained with confidence on the preponderant bulk of normal VLDL. For the first time we report the CD spectra of human VLDL and IDL. In contrast with human LDL and the lipoproteins of the hypercholesterolemic rabbit, the entire CD SPECTRUM OF HUMAN VLDL shows increased ellipticity with decreasing temperature, which is completely reversible. We have found that the protein moieties of human VLDL and IDL contain substantially more helix (approximately 50%) than does that of human LDL.

Animals↗
PubMed1990

[Construction and application of atropine flow-through sensor in flow injection analysis].

A new kind of flow-through sensor for atropine has been studied. It exhibits Nernstian response for atropine with a slope of 54 +/- 1 mV/decade over the concentration range of 0.02-200 mmol/L at pH 5-8. The sensitivity coefficients of common compounds were determined. Only bromo-geramine, clonidine, strychnine and amantadine showed remarkable interference. Direct potentiometry for determination of atropine showed an average recovery of 99.2% and a relative standard deviation of 1.3%. It has been used in flow injection analysis (FIA) of atropine, anisodamine and scopolamine and belladonna preparations. Rate of analysis of as high as 60-100 samples/h was achieved.

Atropa belladonna↗
PubMed1989

[Study and application of atropine field-effect transistor].

Atropine-H2SO4 is widely used in clinic. The atropine sensitive electrode has been prepared, but Atropine field-effect transistor (Atropine-FET) has not been reported. In this communication, electro-active material is atropine tetraphenylboron. The sensor was fabricated by coating solution composed of electro-active material, dibutyl phthalate (DBP) and 5% PVC in tetrahydrofuran (THF) on Pt wire of gate electrode of MOSFET. The sensor showed linear response to atropine within concentration range 2.0 x 10(-2)-6.3 x 10(-5) mol/L. The slope of the sensor was 55 mV/decade and the limit of detection was 1.6 x 10(-5) mol/L. The sensor response was not affected by pH in the range 3.2-8.2, and the sensor can be used for the determination of atropine sulphate in drug-substances by direct potentiometry. The results of determination were in agreement with the data obtained by the official method in Chinese Pharmacopoeia. The method appears to be a rapid, simple and precise one.

Atropine↗
PubMed1987

EPR characterization of the iron-sulfur clusters in the NADH: ubiquinone oxidoreductase segment of the respiratory chain in Paracoccus denitrificans.

The physicochemical properties of the iron-sulfur clusters present in the NADH:ubiquinone oxidoreductase of Paracoccus denitrificans have been examined in the cytoplasmic membrane particles by redox potentiometry and EPR spectroscopy. Analogous to the iron-sulfur clusters present in the mitochondrial NADH: ubiquinone oxidoreductase, we have found two binuclear and three tetranuclear EPR detectable iron-sulfur clusters, namely, N-1a, N-1b, N-2, N-3, and N-4. In the bacterial system, the two binuclear clusters differ in line shape and in Em values; the cluster with more rhombic symmetry (gx,y,z = 1.918, 1.937, 2.029) has the Em7.0 value of -150 while the almost axial one (gx,y,z = 1.929, 1.941, 2.019) has Em7.0 of -270 mV. The Em of the former cluster is pH dependent (-60 mV/pH) as in the case of mammalian N-1a while the latter is pH independent as is the mammalian cluster N-1b. The pH-dependent P. denitrificans [2Fe-2S] cluster, which we have labeled N-1a, has an Em7.0 as high as that of N-2, in contrast to the mammalian N-1a. Thus N-1a is reducible with a physiological reductant, NADH in this bacterial system. The Em of the cluster N-2 is also pH dependent (Em7.0 = -130 mV) with a pK value near 7.7. The Em values of all other clusters exhibit no pH dependence as in the case of their mammalian counterparts. We have found that the cluster N-1a is the most labile component among the five iron-sulfur clusters and may give rise to variable relative spin concentrations and extremely low Em values due to the facile modifications of the microenvironment of the cluster. The P. denitrificans NADH:ubiquinone oxidoreductase provides a unique and useful site I model system where redox composition is similar to the mitochondrial enzyme but with fewer numbers of polypeptides (Yagi, T. (1986) Arch. Biochem. Biophys. 250, 302-311).

Animals↗
PubMedDate not supplied

[Enzymatic hydrolysis of fat in the presence of Lamblia duodenalis (in vitro)].

The influence of Lamblia on the hydrolysis of fat by lipase was studied in vitro. The hydrolysis rate of fat in the presence of live Lamblia and without them was determined colorimetrically by the quantity of the formed glycerine. In addition, the kinetics of this reaction was studied by the method of compensating potentiometry by neutralization of fat acids with alkali. The intact organisms were found to cause an inhibition of fermentative hydrolysis of fat. The importance of this fact from the point of view of interaction in the host-parasite system is discussed.

Giardia↗
PubMedDate not supplied

[Comparative study of the rate of glucose and oxygen consumption by bacteria normally and under the action of low temperatures].

The effect of freezing on the rate of respiration and glucose assimilation in Escherichia coli M-17 incubated in 2 mM phosphate buffer, physiological solution, and media containing 1% and 10% glycerol was studied by potentiometry and delayed fluorescence of bacterial cells. When the cells were frozen to --70 degrees C and the rate of freezing-thawing was 10--15 degrees C per 1 min, the rate of respiration and glucose assimilation was below the stationary level, and the restoration took 20--60 min depending on the incubation medium. The low activity of the cells is attributed to the disturbed permeability of bacterial membranes, in particularly, for H+ ions.

Cell Membrane Permeability↗
PubMed1984

Thermodynamic properties of the semiquinone and its binding site in the ubiquinol-cytochrome c (c2) oxidoreductase of respiratory and photosynthetic systems.

The antimycin-sensitive ubisemiquinone radical (QC) of the ubiquinol-cytochrome c oxidoreductase of submitochondrial particles and chromatophores of Rhodopseudomonas sphaeroides Ga has been studied by a combination of redox potentiometry and EPR spectroscopy. This g = 2.005 radical signal appears at physiological pH values and increases in intensity with increasing pH up to pH 7.6 in submitochondrial particles and pH 9.0 in R. sphaeroides after which its intensity remains unchanged. The Em7 (ubiquinone/quinol) of the signal, estimated from redox titration data is 80 mV for submitochondrial particles, and 150 mV in chromatophores. Each of these values is higher than that of the quinone pool by 20 mV in submitochondrial particles and 60 mV in R. sphaeroides. This indicates that the quinone at the binding site is out of equilibrium with the pool, and that binding site preferentially binds quinol over quinone. Analysis of the shapes of the semiquinone titration curves, taken together with the midpoint elevation, indicates a quinone-binding site: cytochrome c1 stoichiometry of 1:1 in both submitochondrial particles and chromatophores. At its maximal intensity, the semiquinone concentration at the binding site is 0.26 in submitochondrial particles (greater than pH 7.6) and 0.4 in chromatophores (greater than pH 9.0). In both systems, the midpoint of the ubiquinone/ubisemiquinone couple is constant as the pH is raised up to the pH of maximal semiquinone formation whereafter it becomes more negative at the rate of -60 mV/pH unit. The midpoint of the ubisemiquinone/quinol couple, on the other hand, varies by -120 mV/pH unit at pH values up to the transition pH, after which it, too, changes by -60 mV/pH unit. This seemingly anomalous behavior may be explained by invoking a protonated group at or near the quinone-binding site whose pK corresponds to the pH transition point in the quinone/semiquinone/quinol redox chemistry when the site is free or when quinone or quinol occupies the site. This pK is elevated to at least pH 9.0 in submitochondrial particles and 10.5 in R. sphaeroides when semiquinone is bound to the site.

Animals↗
PubMed1984

Reversible photoreduction of flavin with bilirubin II.

Bilirubin react with flavins under both aerobic and anaerobic conditions. Under anaerobic conditions these substances behave as a redox-system in solution, riboflavin functioning as an electron acceptor and bilirubin as an electron donor. The reaction products are the leuco-form of riboflavin and biliverdin. On the basis of the dependence of the optical spectrum and of the reaction rate on pH it can be assumed that bilirubin reacts in the anionic form. Under anaerobic conditions a reversible reaction occurs leading to a dynamic equilibrium of the reactants. The products were identified and determined by optical spectroscopy, chromatography and potentiometry. Excretion of biliverdin in the stool of new-born infants was orientatively monitored during the phototherapy of hyperbilirubinemia, after the administration of small doses of riboflavin. It has been found that excretion of biliverdin increases during the phototherapy. The possibility of utilizing the described reaction for an improvement in the phototherapy of new-born infant hyperbilirubinemia is discussed.

Bilirubin↗