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PubMed1984

Analysis of hepatic reduced glutathione, cysteine and homocysteine by cation-exchange high-performance liquid chromatography with electrochemical detection.

A high-performance liquid chromatographic method employing a mercury-based electrochemical detector and a cation-exchange column is described for the simultaneous measurement of reduced glutathione, cysteine, and homocysteine in liver homogenates. Sample preparation involves precipitation of protein with perchloric acid, removal of perchlorate by precipitation as its potassium salt and dilution with mobile phase. Mercaptoethylglycine is used as the internal standard. Using this procedure, the sum of the individual hepatic thiols agreed well with the total thiols determined with Ellman's reagent. Comparisons were made with (a) control rats, (b) rats depleted of hepatic thiols by pargyline pretreatment, and (c) rats administered L-cysteine.

Animals↗
PubMed1998

Determination of fluoxetine and norfluoxetine in human plasma by high-pressure liquid chromatography with fluorescence detection.

Fluoxetine is an atypical antidepressant drug, which selectively inhibits the neuronal reuptake of serotonin, and is widely used in the treatment of depressive disorders. The aim of this research is the development of an HPLC method with fluorescence detection for the monitoring of fluoxetine plasma levels. The determination requires no more than 250 microl of plasma, which undergo solid phase extraction (SPE), then are injected in the HPLC. For the analytical separation a reversed phase C8 column (150 x 4.6 mm I.D.) was used, while the mobile phase was a mixture of acetonitrile and water containing perchloric acid and tetramethylammonium perchlorate (flow rate: 1 ml min(-1)). The very low levels of analytes in plasma required the employment of a fluorescence detector (lambda(exc) = 230 nm, lambda(em)=290 nm), which also granted a good selectivity. Fluoxetine is revealed as a single peak at a retention time of 9.7 min, while norfluoxetine, the main metabolite of fluoxetine, is revealed at a retention time of 8.1 min. Linearity was obtained over the concentration range 8-200 ng ml(-1) for both substances. The method seems suitable, in accuracy and precision, for the determination of fluoxetine plasma levels of patients; furthermore, it is rapid and sensitive.

Calibration↗
PubMed1992

Mechanism of the conformational transition of melittin.

It is known that, while melittin at micromolar concentrations is unfolded under conditions of low ionic strength at neutral pH, it adopts a tetrameric alpha-helical structure under conditions of high ionic strength, at alkaline pH, or at high peptide concentrations. To understand the mechanism of the conformational transition of melittin, we examined in detail the conformation of melittin under various conditions by far-UV circular dichroism at 20 degrees C. We found that the helical conformation is also stabilized by strong acids such as perchloric acid. The effects of various acids varied largely and were similar to those of the corresponding salts, indicating that the anions are responsible for the salt- or acid-induced transitions. The order of effectiveness of various monovalent anions was consistent with the electroselectivity series of anions toward anion-exchange resins, indicating that the anion binding is responsible for the salt- or acid-induced transitions. From the NaCl-, HCl-, and alkaline pH-induced conformational transitions, we constructed a phase diagram of the anion- and pH-dependent conformational transition. The phase diagram was similar in shape to that of acid-denatured apomyoglobin [Goto, Y., & Fink, A.L. (1990) J. Mol. Biol. 214, 803-805] or that of the amphiphilic Lys, Leu model polypeptide [Goto, Y., & Aimoto, S. (1991) J. Mol. Biol. 218, 387-396], suggesting a common mechanism of the conformational transition. The anion-, pH-, and peptide concentration-dependent conformational transition of melittin was explained on the basis of an equation in which the conformational transition is linked to proton and anion binding to the titratable groups.

Anions↗
PubMed1998

Fluorometric analysis of 2-thiobarbituric acid reactive substances in turkey.

Three experiments were conducted to develop a sensitive and reliable fluorometric thiobarbituric acid (TBA) reactive substances (TBARS) method to determine lipid oxidation products in meat. The first study was conducted to find the optimum sample preparation conditions for meat in the fluorometric method. The second study was to compare the original and the modified methods by using meat and blood samples. The modified fluorometric method was compared with a conventional spectrophotometric method in a third study. Four different extraction solutions (2.5 M acetic acid, 0.5 M hydrochloric acid, 0.8 M perchloric acid, and 1.4 M trichloroacetic acid) and two ratios of extraction solution to TBA (20 mM) solutions (2:1 and 1:1) were examined in the first study. Hydrochloric acid was the optimum among the four extraction solutions tested, and the ratio of extraction solution to TBA solution at 1:1 was the best for the fluorometric TBARS method in raw ground turkey. The modified fluorometric method had high recovery rates (91%, average), and the regression coefficient of the standard curve prepared with spikes was also high (r2 = 0.99). The analysis of raw meat and plasma samples indicated that the modified fluorometric method had greater sensitivity than the original method. The pH of the reaction mixture played an important role in extraction TBARS from samples, and low pH conditions were preferable to high pH conditions. The amount of lipid oxidation products in raw turkey breast meat indicated that the fluorometric method had much greater sensitivity than the spectrophotometric method. The results from the three studies showed that the modified fluorometric TBARS method was useful for the samples with low lipid oxidation products, such as fresh raw meat. The sensitivity of the modified fluorometric method also facilitates the determination of oxidation products in small quantities of samples.

Animals↗
PubMed1996

Salivary factors in vomiting bulimics with and without pathological tooth wear.

The increased occurrence of dental erosion from self-induced vomiting in bulimia nervosa is not linearly associated with the frequency or the duration of vomiting. Possible changes in the buffering and lubricating role of saliva in bulimia nervosa and their relationship to erosion have not been previously investigated. Chewing-gum-stimulated salivary flow rate, pH, bicarbonate concentration and viscosity were compared between two groups of vomiting bulimics and with 10 healthy controls. One bulimic group (n = 9) had pathological tooth wear present according to the criteria of the Tooth Wear Index and the other bulimic group (n = 10) did not. The influence of salivary pellicle on enamel acid dissolution by perchloric acid was also assessed by an enamel biopsy method. Bicarbonate was measured in a Natelson microgasometer. Both the bulimic groups had mean initial 3-min flow rates and overall 9-min flow rates significantly lower (p < 0.01) than the healthy subjects. The mean pH values were not significantly different between the two bulimic groups or the control group. However, the mean bicarbonate concentration in both bulimic groups was significantly less (p < 0.01) than in the control group. The mean salivary viscosity of 7.4 centipoise (cP), measured by a DV1 Brookfield viscometer, was significantly greater (p < 0.05) in the pathological tooth-wear-present group than in the tooth-wear-absent group (4.5 cP) and the control group (4.1 cP). Slightly more calcium was released from the pellicle-free surface in both groups but this was not statistically significant, whilst the dissolved calcium in enamel biopsies was significantly lower (p < 0.05) in the tooth-wear-present group.

Adult↗
PubMed2005

Metals distribution and interactions in tissues of shrews (Sorex spp.) from copper- and zinc-contaminated areas in Poland.

To assess the risk from heavy metal accumulation to insectivorous species exposed to different pollutants, shrews [Sorex araneus (Linnaeus 1758) and Sorex minutus (Linnaeus 1766)] were collected in the Olkuski Ore Region (OOR; a Zn and Cd smelter area), Legnicko-Głogowski Copper Mine Region (LGCR; a copper ore-mining area), and Białowieza Forest (BF; a control area). A few sites were chosen in each region and a total of 57 animals were collected from them. The liver and kidneys were dissected from the animals, dried, and digested in a 4:1 mixture of HNO3 (nitric acid) and HClO4 (perchloric acid). Cadmium, lead, zinc, copper, and iron were determined in the samples by flame or flameless atomic absorption spectrometry. The interactions between toxic and essential metals were calculated for each tissue. The data showed that accumulation of metals by insectivores is high; shrews accumulated much higher amounts of cadmium and lead than bank voles, studied by other researchers, from the same areas. The expected high tissue accumulation of copper at LGCR and zinc at OOR was not seen, but the levels of both elements were higher in the tissues of shrews from OOR than from LGCR. The lowest copper concentrations were in the tissues of shrews from BF. The highest cadmium and lead concentrations were found in the tissues of shrews from OOR. Some significant correlations were found between the tissue concentrations of xenobiotic and essential metals (e.g., between cadmium and zinc and between lead and iron).

Analysis of Variance↗
PubMedDate not supplied

Determination of phosphorus in fertilizers by inductively coupled plasma atomic emission spectrometry.

An inductively coupled plasma atomic emission spectrometry (ICP-AES) method was developed for the determination of phosphorus in fertilizers. Total phosphorus, direct extraction available phosphorus (EDTA), and water-soluble phosphorus, reported as phosphorus pentoxide (P205), in 15 Magruder check fertilizers were measured by ICP-AES, and the results were compared with those obtained by the AOAC official method. Five analytical wavelengths of phosphorus, 177.499, 178.287, 213.618, 214.914, and 253.565 nm, were tested for the determination of phosphorus in fertilizers, and their detection limits were obtained. Acid effects of perchloric acid and possible matrix effects of aluminum, calcium, magnesium, potassium, and sodium were negligible for phosphorus determination. Wavelength 213.618 nm was the best analytical wavelength for phosphorus determination by all 3 sample preparation methods for the selected Magruder fertilizers. The results demonstrated that the accuracy and precision of the ICP-AES method were comparable with those of the official methods.

Acids↗
PubMed1979

Extraction of human plasma or sera by heat treatment for a solid-phase radioimmunoassay of carcinoembryonic antigen.

Heat treatment and a solid-phase radioimmunoassay are combined to give a relatively simple and rapid procedure for assay of carcinoembryonic antigen in plasma or serum. The new way we describe to extract this antigen is an alternative to the conventional method of extraction with perchloric acid. Heating plasma or serum samples in acetate buffer (0.16 mol/L, pH 5.0) at 70 degrees C for 15 min precipitates out most of the heat-labile, nonspecific plasma proteins, but leaves most of the antigen in solution, with its immunochemical properties apparently unaffected. Comparison between the heat treatment and the perchloric acid extraction yielded comparable values when tested either by solid-phase radioimmunoassay or by the zirconyl phosphate precipitation method. An added advantage of our method is that it gives the same assay values for both plasma and serum. Results for a group of pathological plasma samples, assayed by both our method and the perchloric acid-zirconyl phosphate precipitation method, gave a correlation coefficient of 0.90.

Carcinoembryonic Antigen↗
PubMed1987

Identification of inositol hexaphosphate in 31P-NMR spectra of Dictyostelium discoideum amoebae. Relevance to intracellular pH determination.

A sugar phosphomonoester, myo-inositol hexakisphosphate (phytic acid), has been identified as a major phosphorylated metabolite in Dictyostelium discoideum amoeba. Its intracellular concentration was estimated to be 0.7 mM. The identification was made in perchloric acid extracts on the basis of 31P-NMR chemical shift values and their variations with pH, by addition of authentic compound and by hydrolysis with wheat phytase. Perchloric acid extracts were prepared so as to avoid losses of insoluble salts of polyphosphorylated compounds with divalent cations. The glycolytic intermediate, 3-phosphoglycerate accumulated intracellularly in amoebae incubated in the presence of fluoride. The pH sensitive NMR signal of 3-phosphoglycerate was used to monitor cytosolic pH and a value of pH 7.4 was found in aerobic Dictyostelium amoebae.

6-Phytase↗
PubMed1985

Natural-abundance 13C NMR of brain.

In natural-abundance 13C NMR spectrum of excised rat brain 55 resonances were resolved. The chemical shifts of most of the resonances were well correlated with those of pure brain metabolites, determined under identical experimental conditions. These resonances were also found in the cytosol fraction and perchloric acid extract of the brain. Some brain resonances were not observed in the perchloric acid extract but only in the microsomes or cytosol.

Animals↗
PubMed2005

Determination of plasma and brain levels of isotretinoin in mice following single oral dose by high-performance liquid chromatography.

An isocratic reversed-phase high-performance liquid chromatographic method was established and validated according to FDA's Guidance for Industry, "Bioanalytical Method Validation", for the determination of isotretinoin in plasma and brain tissue from mice following single and multiple oral doses of Accutane. Plasma sample preparation included deproteination with acetonitrile-perchloric acid followed by centrifugation. Brain tissue was homogenized and extracted with acetonitrile-perchloric acid followed by centrifugation. The supernatants were analyzed by high-performance liquid chromatography (HPLC). Benz[alpha]anthrancene-7,12-dione was used as the internal standard. Chromatographic separation was achieved on a C18 column using an acetonitrile-aqueous 0.5% acetic acid (85:15, v/v) elution. The average extraction efficiency was >95% for plasma and >82% for brain. The lower limit of quantification was 30 ng/mL for plasma and was 30 ng/0.1g for brain tissue, respectively. The linear range for plasma was 30-600 ng/mL, and 15-300 ng/0.1g for brain. Maximum concentrations of isotretinoin in both plasma and brain were observed at 1h after single oral dosing (25 mg/kg). The maximum concentrations in plasma and brain were 2.36 microg/mL and 0.34 microg/g, respectively. The mean area under curve (AUC) in plasma was 6.13 microg h/mL. The mean eliminate half-life in plasma was estimated as 46 min.

Administration, Oral↗
PubMed2002

Flash photolytic generation and study of p-quinone methide in aqueous solution. An estimate of rate and equilibrium constants for heterolysis of the carbon-bromine bond in p-hydroxybenzyl bromide.

Flash photolysis of p-hydroxybenzyl acetate in aqueous perchloric acid solution and formic acid, acetic acid, biphosphate ion, and tris(hydroxymethyl)methylammonium ion buffers produced p-quinone methide as a short-lived species that underwent hydration to p-hydroxybenzyl alcohol in hydronium ion catalyzed (k(H(+)) = 5.28 x 10(4) M(-1) s(-1)) and uncatalyzed (k(uc) = 3.33 s(-1)) processes. The inverse nature of the solvent isotope effect on the hydronium ion-catalyzed reaction, k(H(+))/k(D(+)) = 0.41, indicates that this process occurs by rapid and reversible protonation of the quinone methide on its carbonyl carbon atom, followed by rate-determining capture of the p-hydroxybenzyl carbocation so produced by water, while the magnitude of the rate constant on the uncatalyzed process indicates that this reaction occurs by simple nucleophilic addition of water to the methylene group of the quinone methide. p-Quinone methide also underwent hydronium ion-catalyzed and uncatalyzed nucleophilic addition reactions with chloride ion, bromide ion, thiocyanate ion, and thiourea. The solvent isotope effects on the hydronium ion-catalyzed processes again indicate that these reactions occurred by preequilibrium mechanisms involving a p-hydroxybenzyl carbocation intermediate, and assignment of a diffusion-controlled value to the rate constant for reaction of this cation with thiocyanate ion led to K(SH) = 110 M as the acidity constant of oxygen-protonated p-quinone methide. In a certain perchloric acid concentration range, the bromide ion reaction became biphasic, and least-squares analysis of the kinetic data using a double-exponential function provided k(Br(-)) = 3.8 x 10(8) M(-1) s(-1) as the rate constant for nucleophilic capture of the p-hydroxybenzyl carbocation by bromide ion, k(ionz) = 8.5 x 10(2) s(-1) for ionization of the carbon-bromine bond of p-hydroxybenzyl bromide, and K = 4.5 x 10(5) M(-1) as the equilibrium constant for the carbocation-bromide ion combination reaction, all in aqueous solution at 25 degrees C. Comparisons are made of the reactivity of p-quinone methide with p-quinone alpha,alpha-bis(trifluoromethyl)methide as well as p-quinone methide with o-quinone methide.

Hydrocarbons, Brominated↗
PubMed1991

Abnormal tau proteins from Alzheimer's disease brains. Purification and amino acid analysis.

Abnormal tau proteins (PHF-tau) were isolated from Alzheimer's disease brains by treatment of paired helical filament enriched-fractions with perchloric acid and boiling of the acid precipitable fraction with beta-mercaptoethanol. These proteins were purified further by a second perchloric acid treatment. The purified PHF-tau proteins were soluble in buffers devoid of sodium dodecyl sulfate. However, they were similar to the abnormal tau extracted from paired helical filaments with sodium dodecyl sulfate, also named A68, in molecular mass (68, 64, and 60 kDa), isoelectric point (pI 5.5-6.5), reactivity with anti-tau antibodies, and in requirement for alkaline phosphatase treatment to bind the Tau-1 antibody. Compared to normal tau, the soluble PHF-tau contained 100% more glycine and 35% less lysine residue. The results suggest that besides phosphorylation other types of modification may be involved in differentiating PHF-tau from normal tau.

Alzheimer Disease↗
PubMed2005

Photochemistry of the alkaloids eudistomin N (6-bromo-nor-harmane) and eudistomin O (8-bromo-nor-harmane) and other bromo-beta-carbolines.

The UV-absorption, fluorescence excitation and emission spectra of the alkaloids eudistomin N (6-bromo-nor-harmane) and eudistomin O (8-bromo-nor-harmane) were described. In order to perform a comparative analysis, we also studied other bromo-beta-carbolines and the corresponding non-substituted-carboline. Thus, 6-bromo-, 8-bromo-, 6,8-dibromo-, 3,6-dibromo- and 3,6,8-tribromo-derivatives of nor-harmane, harmane and harmine were studied. These studies were performed in EtOH and in EtOH + 1% perchloric acid solutions (pa). Furthermore, fluorescence quantum yields (phi(f)) in acetonitrile and acetonitrile + 1% perchloric acid solutions at 298 K were measured. The HOMO and LUMO energy, the positions (lambda(max)) and oscillator strength (f) of the (1)S(1) <--(1)S(0) band for all the neutral and protonated beta-carbolines studied was calculated and compared with the experimental data. The pK(a) values in aqueous solution for eudistomin N and O (6-bromo- and 8-bromo-nor-harmane), for 6-bromo-, 8-bromo- and 6,8-dibromo-harmane, and for 6-bromo- and 8-bromo-harmine were spectrophotometrically measured (pK((a)(H(2)O))) . The change of the acid-base character of these compounds on going from the ground state (pK(a)) to the first electronic excited singlet state (pK(a)(*)) as DeltapK(a) = pK(a)(*)-pK(a) = 0.625 Deltanu /T, in ethanol solution at 298 K were calculated (DeltapK(a(EtOH))). Proton affinities (PA) for all the compounds studied defined as minus the enthalpy change of the reaction M+H(+)--> MH(+) (gas state) were calculated. Basicity relative to pyridine (DeltaH(rPy)) defined as the enthalpy change of the isodesmic reaction MH(+) + Py--> M + PyH(+) (gas state) was also calculated. The effect of bromine as substituent on the properties of the beta-carboline moiety in nor-harmane, harmane and harmine is discussed.

Carbolines↗
PubMed1986

An assay for ribonuclease activity, based on ultraviolet absorption of RNA hydrolysate, using phosphotungstic acid.

In the method for the determination of ribonuclease activity that depends on the ultraviolet absorption of the RNA hydrolysate, the uranium reagent (25% perchloric acid solution containing 0.75% uranyl acetate) is commonly used for the efficient precipitation of the unhydrolyzed RNA. However, this reagent is always contaminated by the presence of radioactive isotopes. Radioactive uranium is one of the substances used for atomic nuclear fuel and therefore, at least in Japan, the use of uranium compounds requires permission from the government. We tried to find another efficient and non-radioactive precipitant of RNA to replace the uranium reagent, and have developed a phosphotungsten reagent (25% perchloric acid solution containing 0.75% phosphotungstic acid plus 0.6% bovine serum albumin solution) which functions as efficiently as the uranium reagent in the precipitation of RNA. A cell-free crude extract of Dictyostelium discoideum was used as the source of ribonuclease.

Chemical Precipitation↗
PubMed1990

On the paradoxically concentration-dependent metabolism of 6-mercaptopurine in WEHI-3b murine leukemia cells.

The intracellular metabolism of 6-mercaptopurine (6-MP) was studied in a murine leukemia cell line, WEHI-3b. Cells were incubated 3 to 24 h with 10 nM to 50 microM 6-MP. Nucleotides were extracted with perchloric acid, and the 6-thiopurine nucleotides were isolated on mercurial cellulose. The endogenous ribonucleotides in the perchloric acid extracts as well as 6-thiopurine nucleotides were separated and quantified with anion exchange high-performance liquid chromatography. The concentration of 6-thioinosinate (6-TIMP) and 6-thioxantinate (6-TXMP) increased with an increasing 6-MP dose. The concentration of the 6-thioguanosine nucleotides (6-TGN) increased with 6-MP concentrations between 10 nM and 1 microM. However, further increase in 6-MP concentration led to a decrease in the formation of 6-TGN. At 50 microM 6-MP, the concentration of 6-thioguanosine 5'-triphosphate was one fifth of that seen at 1 microM. The incorporation of 6-[35S]mercaptopurine into DNA was also slightly higher at 1 microM compared with 50 microM. The cytocidal effect on clonogenic cells was one log greater at 1 microM 6-MP compared with 50 microM 6-MP. The decrease of 6-TGN was accompanied not only by an increased 6-TIMP concentration but also by an inhibition of the purine de novo synthesis and consequently by a decrease of the cellular ATP concentration. The ATP concentration in the cells treated with 1 microM 6-MP could be reduced to the level seen in cells treated with 50 microM 6-MP by simultaneous incubation with 0.3 microM antimycin A. This decrease of ATP concentration was accompanied by a reduction of 6-TGN and to a lesser extent of 6-TXMP. These experiments suggest that the "self-limiting" phenomenon in the metabolism of 6-MP might be caused by a depletion of ATP by inhibition of purine de novo synthesis presumably by 6-TIMP.

Animals↗
PubMed1986

Microtubule-associated protein tau. A component of Alzheimer paired helical filaments.

Microtubule-associated protein tau was purified from bovine brain microtubules by either (1) phosphocellulose chromatography, (2) heat treatment at pH 6.4, (3) heat treatment at pH 2.7, (4) heat treatment at pH 2.7 followed by extraction with perchloric acid and precipitation with glycerol, or (5) by precipitation with ammonium sulfate followed by extraction with perchloric acid. All of these tau preparations reacted specifically with antibodies to Alzheimer paired helical filaments. Affinity purified antibodies to tau labeled both Alzheimer neurofibrillary tangles and plaque neurites but not amyloid in Alzheimer brain tissue sections and labeled paired helical filament polypeptides on Western blots. Human brain tau and paired helical filament polypeptides co-migrated on sodium dodecyl sulfate-polyacrylamide gels. These results suggest that tau is a major component of Alzheimer paired helical filaments.

Alzheimer Disease↗