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PubMed1998

Association of serum albumin concentration, serum ionized calcium concentration, and blood pressure in the Third National Health and Nutrition Examination Survey.

A few small studies of white persons have found a positive association between serum albumin and blood pressure. However, this association might be due to ionized calcium. No data on albumin or ionized calcium have appeared for African Americans or Hispanics, and few for women. To explore the association of serum albumin (g/L) and ionized calcium (mmol/L) with both systolic and diastolic blood pressure, data from the Third National Health and Nutrition Examination Survey, 1988-94, were analyzed. Results from multiple regressions, controlling for age, overweight, alcohol intake, hematocrit, pulse, antihypertensive medication, and smoking indicate that serum albumin is positively correlated (P < 0.01) to systolic and diastolic blood pressure among non-Hispanic white men 25-59 and 60-89 years old. Ionized calcium was associated negatively with diastolic blood pressure among younger Mexican-American men. In this national sample, serum albumin was consistently associated with systolic and diastolic blood pressure only among non-Hispanic white men.

Adult↗
PubMed2003

The relationship between ionized and total serum magnesium concentrations during abdominal surgery.

STUDY OBJECTIVE: To determine the necessity for ionized magnesium (iMg) assay by evaluating the effect of abdominal surgery without massive transfusion on total magnesium (Mg) and iMg concentrations. DESIGN: Prospective, observational study. SETTING: Operating rooms at a university teaching hospital. PATIENTS: 31 patients without electrolyte abnormalities who were scheduled for abdominal surgery. INTERVENTIONS: None. MEASUREMENTS: Serum electrolytes, iMg, ionized calcium, proteins before and after surgery, and urine Mg were recorded. MAIN RESULTS: Total Mg and iMg decreased: Mg 23%, iMg 15%; p < 0.0001. Total and iMg were highly correlated (r = 0.728, p < 0.0001). Urine Mg output remained within normal limits (mean 0.24 mmol/hr). CONCLUSIONS: During abdominal surgery without massive transfusion, both total and ionized hypomagnesemia occur. Changes in iMg and total serum Mg concentrations are closely correlated. Total serum Mg assay, while overestimating the prevalence of ionized hypomagnesemia, is sufficient to screen for hypomagnesemia.

Abdomen↗
PubMed1998

The anesthetic isoflurane decreases ionized calcium and increases parathyroid hormone and osteocalcin in cynomolgus monkeys.

The effects of anesthetics on calcium metabolism in cynomolgus monkeys were studied. Eight adult female cynomolgus monkeys were used in a crossover design. Blood was collected from each of the monkeys at four timepoints: (1) while conscious; (2) following induction of anesthesia with ketamine, ketamine and atropine, isoflurane, or no anesthetic; (3) at 30 min; and (4) 120 min thereafter. Four experiments were performed with a 1 week washout period between sessions, such that each monkey received each treatment. Potassium was lower in anesthetized monkeys than in those that remained conscious. Cortisol, although high, did not differ among anesthetic treatments. Ketamine and ketamine/atropine did not consistently affect ionized calcium or parathyroid hormone (PTH) concentrations. Isoflurane decreased ionized calcium (0.05 mmol/L), and increased PTH and osteocalcin twofold. The serum inorganic fluoride concentration was higher in monkeys anesthetized with isoflurane than with ketamine/atropine, which may partially account for the decrease in ionized calcium with isoflurane. The increases in PTH and osteocalcin are presumably secondary to the decrease in ionized calcium.

Anesthetics, Inhalation↗
PubMed2000

Gas sampling glow discharge: a versatile ionization source for gas chromatography time-of-flight mass spectrometry

A gas chromatograph has been coupled to a direct-current gas sampling glow discharge (GSGD) ionization source for the mass spectrometric analysis of halogenated hydrocarbons. The continuous discharge is contained within the first vacuum stage of the differentially pumped spectrometer interface. The discharge can be operated statically or rapidly switched between atomic and molecular ionization modes; both atomic and molecular spectra could be generated in the helium-supported plasma. In the switched configuration, the duty cycle is 50% for each mode. The ionization mode is selected by application of either a positive (molecular) or negative (atomic) potential to the sample introduction electrode, and the two kinds of spectra can be sequentially collected by changing the voltage and current between two preset values. Similar ion-optical voltage settings could be employed for both modes of operation, with the exception of the steering-plate potential, which had to be modulated between two different values (at the plasma switching frequency) to obtain the greatest atomic and molecular signal levels. The source is capable of generating mass spectra resembling those from an electron-impact source while operated in the molecular ionization mode (both static and dynamic). The best atomic detection limits (1-25 fg of analyte/ second) were obtained when the plasma was operated in the static mode with single-channel gated ion counting. Atomic detection limits obtained with boxcar averager data collection were comparable for static and switched operation of the source (1-30 pg/s). Likewise, the molecular detection limits were similar for the static and switched modes and span the range of 7-140 pg/s (boxcar averagers). Precision was better than 7% RSD under all conditions. The atomic and molecular chromatographic peak heights were nearly unchanged over a range of modulation rates from 5 to 100 Hz. The elemental ratio (35Cl+/12C+) for chloroform was also measured over a range of plasma modulation rates (5-90 Hz) and found to be randomly distributed about the sample mean. Several chlorinated hydrocarbons were introduced into the discharge and could be successfully differentiated (or speciated) on the basis of their 35Cl+/12C+ ratios.

Journal Article↗
PubMed2000

A REMPI method for the ultrasensitive detection of NO and NO2 using atmospheric pressure laser ionization mass spectrometry.

We report on the development of a quasi-simultaneous highly selective method for NO and NO2 detection at the ultratrace level. Atmospheric pressure laser ionization (APLI), recently introduced by our group, is used to detect both compounds at low parts per trillion by volume (pptv) mixing ratios. APLI is based on resonance-enhanced multiphoton ionization mass spectrometry. Two-color pump-probe experiments employing a single excimer pumped dye laser combination allow for the ultrasensitive measurement of NO and NO2 within a narrow range of maximum pumping efficiency of the laser dye Coumarin 120. NO is detected via excitation of the long-lived A 2sigma+ (nu' = 1) level at 215.36 nm and subsequently ionized with 308-nm radiation provided by the excimer pump laser. NO2 is ionized after double resonant excitation of the A2B1 and 3psigma manifolds in a (1 + 1' + 1(')) process using 431.65 + 308 nm. The selectivity of the NO measurement exceeds 2,000 with respect to NO2 and N2O5. For NO2, a selectivity of >3,000 with respect to N2O5 and organic nitrates is observed. The current APLI detection limit of NO and NO2 is 0.5 and 5 pptv, respectively, with a 20-s integration time.

Journal Article↗
PubMed1989

Desorption chemical ionization, thermospray, and fast atom bombardment mass spectrometry of dihydropyridine in equilibrium with pyridinium salt-type redox systems.

Trigonellyl-substituted (pyridinium salt type) compounds decompose during sample introduction using desorption chemical ionization (DCI) and thermospray (TSP) ionization. Thermal dequaternization is the main degradation process in DCI, while hydrolytically sensitive bonds are subject to cleavage in the TSP source, and dequaternization and reduction to the dihydropyridine analogues are also observed. Fast atom bombardment (FAB) is the suggested method of ionization because of its ability to provide an intense intact cation. The neutral dihydropyridine analogues can be effectively ionized by DCI and TSP. These methods are recommended, because bombardment-induced oxidation produces artifacts and shows a matrix effect in positive FAB.

Chemical Phenomena↗
PubMed1984

Miniature triaxial metastable ionization detector for gas chromatographic trace analysis of extraterrestrial volatiles.

Gas chromatography has found highly successful application in NASA's flight programs. Gas chromatographs have been flown to both Mars and Venus where detailed compositional measurements were made. These instruments were quite small and relatively sensitive when compared to commercially available instruments; however, they do not appear adequate for future missions currently being planned. The earlier flight GC's had incorporated thermistor bead thermal conductivity cells as the detector. This detector requires very precise temperature control and only provides about 1 ppm sensitivity. Temperature stabilization causes the detector to be quite heavy, i.e., about 200 g. Greater sensitivity will be required for measurements of trace components in extraterrestrial environments. Review of other detector types revealed the metastable ionization detector as a likely candidate because of its superior thermal stability and high sensitivity. The metastable detector, first described by Lovelock as an argon ionization detector, has been studied and somewhat modified by others. The commercial design by Hartmann and Dimick was used for comparison purposes in our work. In the past, three features of the metastable detector are prominent: it has part-per-billion sensitivity, contamination must be carefully controlled, and anomalous response is common. Since it is an ionization detector, however, temperature instabilities do not cause the major perturbations experienced by the thermal conductivity detectors. This paper describes a miniature metastable ionization detector featuring an unconventional electrode configuration, whose performance characteristics parallel those of traditional design, while its weight is quite small. The prototype has been used in our laboratories routinely for 2 years, and the concept will be incorporated into a flight GC for use in the Space Shuttle.

Astronomy↗
PubMed2002

Single photon ionization (SPI) via incoherent VUV-excimer light: robust and compact time-of-flight mass spectrometer for on-line, real-time process gas analysis.

Fast on-line detection of organic compounds from complex mixtures, such as industrial process gas streams, require selective and sensitive analytical methods. One feasible approach for this purpose is the use of mass spectrometry (MS) with a selective and soft (fragment-free) ionization technique, such as chemical ionization (CI) or photo ionization (PI). Single photon ionization (SPI) with vacuum ultraviolet (VUV) light is a particularly sof tionization technique, well-suited for detection of both aromatic and aliphatic species. Problematic, however, is the generation of the VUV light. In general, the vacuum ultraviolet (VUV) light sources for SPI-MS are based either on lasers (e.g., 118-nm radiation generated by frequency-tripling of the third harmonic of a Nd:YAG laser) or on conventional VUV lamps, such as deuterium lamps. Althoughthe laser-based techniques are very sophisticated and expensive, the conventional lamps have serious drawbacks regarding their optical parameters, such as low-output power, low spectral power density, and broad emission bands. In this work, a novel excimer VUV light source, in which an electron beam is used to form rare gas excimer species, is used. The excimer VUV light sourceproduces brilliant and intense VUV light. The novel VUV light source was coupled to a compact and mobile time-of-flight mass spectrometer (TOFMS). A special interface design, including optical (VUV optics) as well as electronic measures (e.g., pulsed ion extraction) was realized. The use of the excimer VUV lamp for SPI will allow the realization of very compact, rugged, and sensitive SPI-TOFMS devices, which preferably will be adapted for process analytical application or monitoring issues (e.g., chemical warfare detection). The excimer VUV-lamp technology delivers VUV light with a good beam quality and high-output power at low costs. Furthermore, it allows changing the emitted wavelength as well as the bandwidth of the excimer VUV lamp in t he 100-200-nm region by changing the gas filling. Consequently, SPI-TOFMS with an excimer light source is a fast detection technique that can be used for online monitoring, for example, in environmental studies or industrial manufacturing processes. In this paper, technology and characteristics of the new excimer light source, as well as the combination with the TOFMS, are presented. Furthermore, a first characterization of the SPI-TOFMS instrument, regarding analytical parameters such as detection limits and selectivity, is given. This includes a discussion of potential improvements that probably will be achievable within a future prototype genertation. Finally, first applications of the system for on-line measurement of organic trace species in a complex gas mixture (here, motorcycle exhaust gas) are presented.

Journal Article↗
PubMed2003

Pulsed-ionization miniature ion mobility spectrometer.

We have demonstrated a miniature ion mobility spectrometer (IMS) that employs single pulses of corona discharge ionization. IMS spectra of both positive and negative ions generated from ambient air were measured as a function of drift field under various ionization conditions. Ion mobility spectra were studied with various pulse widths for both positive and negative ions, giving insights into mechanisms and kinetics of corona discharge ionization used in the miniature IMS. A combination of a pulsed potential with a steady dc bias was used to generate ions in the miniature IMS. There was a threshold dc potential for ion generation for a given pulse height. The dc ionization threshold was found to decrease linearly with increasing pulse height.

Journal Article↗
PubMed2003

Laser desorption combined with hyperthermal surface ionization time-of-flight mass spectrometry.

A setup combining laser desorption of nonvolatile molecules and their aerodynamic acceleration in a supersonic molecular beam followed by hyperthermal surface ionization in a reflectron time-of-flight mass spectrometer is described. While laser desorption performs the intact transfer of the analyte molecules into the gas phase, hyperthermal surface ionization opens up the possibility to efficiently ionize even larger molecules with a small and potentially controlled degree of fragmentation. Being an ionization technique, which is particularly effective for aromatic and heterocyclic compounds, the selectivity can further be increased by tuning the kinetic energy to which the molecules are accelerated in the supersonic beam. The results obtained for several polycyclic aromatic hydrocarbons and biochemical substances show that sufficient acceleration can be achieved even for molecules with a molecular weight above 5000 amu and that HSI preserves its advantageous features even for thermally labile large molecules such as insulin.

Journal Article↗
PubMed2004

Rotation planar chromatography coupled on-line with atmospheric pressure chemical ionization mass spectrometry.

The coupling of a rotation planar preparative thin-layer chromatography system on-line with mass spectrometry is demonstrated using a simple plumbing scheme and a self-aspirating heated nebulizer probe of a corona discharge atmospheric pressure chemical ionization source. The self-aspiration of the heated nebulizer delivers approximately 20 microL/min of the 3.0 mL/min eluate stream to the mass spectrometer, eliminating the need for an external pump in the system. The viability of the coupling is demonstrated with a three-dye mixture composed of fat red 7B, solvent green 3, and solvent blue 35 separated and eluted from a silica gel-coated rotor using toluene. The real-time characterization of the dyes eluting from the rotor is illustrated in positive ion full-scan mode. Other self-aspirating ion source systems including atmospheric pressure photoionization, electrospray ionization, and inductively coupled plasma ionization, for example, might be configured and used in a similar manner coupled to the chromatograph to expand the types of analytes that could be ionized, detected, and characterized effectively.

Journal Article↗
PubMed2000

Chlorine stable isotopes: a comparison of dual inlet and thermal ionization mass spectrometric measurements

Chlorine stable isotope ratios, 37Cl/35Cl, currently are measured using dual-inlet and thermal-ionization mass spectrometry. These two different analytical techniques, however, have never been cross calibrated. A set of samples with chlorine stable isotope delta values ranging from -4.4 to +0.3 % relative to standard mean ocean water chloride has been analyzed using both of these techniques. Our data show that both techniques can yield similar results within analytical uncertainty. CsCl thermal ionization data are extremely sensitive to the amount of chlorine being measured and cannot be used to determine absolute ratios without an independent means of correcting for machine-induced mass fractionation. As long as standards and samples are of equivalent size, however, the differences between samples measured by thermal ionization remain constant Dual inlet stable isotope mass spectrometry is suited best for samples of > 10 micromol Cl, yielding chlorine stable isotope data with < or =0.1% reproducibilities (2sigma). Thermal ionization mass spectrometry easily accommodates samples of approximately0.1-0.3 micromol Cl, with achievable uncertainties of < or =0.2% (2sigma).

Journal Article↗
PubMed1992

Involvement of reactive oxygen intermediates in the induction of c-jun gene transcription by ionizing radiation.

Previous work has demonstrated that the cellular response to ionizing radiation includes transcriptional activation of the c-jun gene. The signaling events responsible for this response, however, remain unclear. The present studies have examined the effects of ionizing radiation on c-jun expression in a variant of HL-60 cells, designated HL-525, which is deficient in protein kinase C (PKC)-mediated signal transduction. The results demonstrate that these cells express low levels of PKC alpha and PKC beta transcripts and exhibit an attenuated induction of c-jun expression following treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA). In contrast, HL-525 cells respond to ionizing radiation with an increase in c-jun mRNA which is more pronounced than that in wild-type HL-60 cells. These cells similarly respond to ionizing radiation with increased expression of the jun-B, jun-D, c-fos, and fos-B genes. Nuclear run-on assays demonstrate that X-ray-induced c-jun expression in HL-525 cells is regulated by increases in the rate of c-jun gene transcription. Moreover, mRNA stability studies in irradiated HL-525 cells demonstrate that the half-life of c-jun transcripts is prolonged compared to that in wild-type cells. Studies with N-acetyl-L-cysteine (NAC), an antioxidant, suggest that X-ray-induced transcriptional activation of the c-jun gene is mediated at least in part through the formation of reactive oxygen intermediates (ROIs). In this context, H2O2 also induced c-jun expression in HL-525 cells, and this effect was inhibited by NAC.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Nucleus↗
PubMed1994

Investigation of ionizable residues critical for sequence-specific enzymatic DNA modification: protein modification and steady-state and pre-steady-state kinetic pH analyses of EcoRI DNA methyltransferase.

Steady-and pre-steady-state pH kinetic analyses are widely used methods to investigate important ionizable groups in enzyme-catalyzed reactions. The first such analysis to identify ionizable residues critical for sequence-specific modification of DNA is presented. EcoRI DNA methyltransferase uses S-adenosyl-L-methionine (AdoMet) to catalyze the N6 methylation of the second adenine in the double-stranded DNA sequence GAATTC. The kinetic mechanism was previously shown to be steady-state-ordered bi bi in which AdoMet binds first followed by DNA addition [Reich, N. O., & Mashhoon, N. (1991) Biochemistry 30, 2933-2939]. Steady-state parameters are strongly dependent on pH and implicate at least four residues with pKa values between 8.2 and 8.9 in the free enzyme and AdoMet-Bound enzyme and one residue with an apparent pKa of 6.0. The data obtained are consistent with the enzyme binding the form of AdoMet in which the alpha amino group is protonated. Two protein residues with an apparent pKa between 8.9 and 9.2 were implicated within the central complex (enzyme-DNA-AdoMet). The general insensitivity of all steady-state parameters to pH changes between pH 6.0 and 8.0 suggests that no critical protein residues undergo ionization-state changes in this range. The lack of significant pH-dependent changes in protein fluorescence and DNA thermal stability suggests minimal structural changes in either macromolecule. In support of the steady-state results single-turnover experiments reveal minimal pH dependence of the methylation rate constant between pH 5.53 and 8.6. Thus, no amino acids critical for catalysis undergo ionization-state changes in this range.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1976

Potentiometric determination of ionizations at the active site of papain.

The ionization behavior of groups at the active site of papain was determined from the pH dependence of the difference of proton content of papain and the methylthio derivative of the thiol group at the active site of papain (papain-S-SCH3). This difference in proton content was determined directly by two independent methods. One method involved potentiometric measurements of the protons released and demethylthiolation of papain-S-SCH3 with dithiothreitol, as a function of pH. The other method involved analogous measurements of the protons released on methylthiolation of papain with methyl methanethiosulfonate. The methylthio pH-difference titrations generated by these measurements indicate that ionization of the thiol group at the active site of papain is linked to the ionization of His-159. The pK of the thiol group changes from 3.3 to 7.6 on deprotonation of His-159 at 29 degrees C/20.05. Similarly, the pK of His-159 shifts from 4.3 to 8.5 when the active site thiol group is deprotonated. The microscopic ionization constants determined in this work for Cys-25 and His-159 indicate that equilibrium constant for transfer of the proton from Cys-25 to His-159 is 8--12, and that in the physiological pH range the active site thiol group exists mainly as a thiol anion.

Binding Sites↗
PubMed2005

Ionization of zwitterionic amine substrates bound to monomeric sarcosine oxidase.

Monomeric sarcosine oxidase (MSOX) binds the L-proline zwitterion (pKa = 10.6). The reactive substrate anion is generated by ionization of the ES complex (pKa = 8.0). Tyr317 was mutated to Phe to determine whether this step might involve proton transfer to an active site base. The mutation does not eliminate the ionizable group in the ES complex (pKa = 8.9) but does cause a 20-fold decrease in the maximum rate of the reductive half-reaction. Kinetically determined Kd values for the ES complex formed with L-proline agree with results obtained in spectral titrations with the wild-type or mutant enzyme. Unlike the wild-type enzyme, Kd values with the mutant enzyme are pH-dependent, suggesting that the mutation has perturbed the pKa of a group that affects the Kd. As compared with the wild-type enzyme, an increase in charge transfer band energy is observed for mutant enzyme complexes with substrate analogues while a 10-fold decrease in the charge transfer band extinction coefficient is found for the complex with the L-proline anion. The results eliminate Tyr317 as a possible acceptor of the proton released upon substrate ionization. Since previous studies rule out the only other nearby base, we conclude that L-proline is the ionizable group in the ES complex and that amino acids are activated for oxidation upon binding to MSOX by stabilization of the reactive substrate anion. Tyr317 may play a role in substrate activation and optimizing binding, as judged by the effects of its mutation on the observed pKa, reaction rates, and charge transfer bands.

Acetates↗
PubMed1996

On the reactivity and ionization of the active site cysteine residues of Escherichia coli thioredoxin.

Within various proteins of the thioredoxin family, the stability of the disulfide bond formed reversibly between the two active site cysteine residues, one accessible and one buried, varies widely and is directly correlated with the pKa value of the accessible cysteine thiol group. If applicable to thioredoxin, its stable disulfide bond would imply that its accessible thiol group should have a high pKa value, whereas it has long been considered to be about 6.7, largely on the basis of the pH dependence of its reactivity. Such kinetic data are shown to be inconsistent with known pKa values in this case; the rate constants may reflect effects in the transition state for the reaction, which is catalyzed by thioredoxin, rather than the protein itself. Ionization of the thioredoxin thiol groups was measured indirectly by the pH dependence of the equilibrium constant for their reaction with glutathione and directly by detection of the thiolate anion by its UV absorbance. Both observations indicated that both cysteine thiol groups of thioredoxin ionize with apparent pKa values in the region of 9-10 and that their ionization is not linked strongly to that of any other groups. This conclusion is not incompatible with the other data available and would make thioredoxin consistent with the relationship between thiol group ionization and disulfide stability observed in other members of the thioredoxin family.

Binding Sites↗
PubMed1997

Regulation of oxidation-reduction potentials through redox-linked ionization in the Y98H mutant of the Desulfovibrio vulgaris [Hildenborough] flavodoxin: direct proton nuclear magnetic resonance spectroscopic evidence for the redox-dependent shift in the pKa of Histidine-98.

Flavodoxin from Desulfovibrio vulgaris is a low molecular weight (15 000 Da) acidic flavoprotein that contains a single flavin mononucleotide (FMN) cofactor. A distinguishing feature of the flavodoxin family is the exceptionally low midpoint potential of the semiquinone/hydroquinone couple. Tyrosine-98, which flanks the outer or si face of the FMN, plays an important role in establishing the oxidation-reduction properties of the bound cofactor as demonstrated by the substitution of a number of amino acids at this position [Swenson, R. P., & Krey, G. D. (1994) Biochemistry 33, 8505-8514]. The midpoint potential for the semiquinone/hydroquinone couple increases substantially when basic residues are introduced at this position. The pH dependency in the Y98H mutant is consistent with a redox-linked ionization model in which the favorable electrostatic coupling between the imidazolium cation and the flavin hydroquinone anion is responsible for the higher potential. Such a model predicts an increase in the pKa of 1.5 units for His98 upon complete reduction of the FMN. In this study, proton nuclear magnetic resonance spectroscopy was used to directly determine the intrinsic pKa of His98 as a function of the redox state of the cofactor in this flavodoxin. Values for the pKa of His98 in the oxidized and fully reduced flavodoxin are 7.02 +/- 0.08 and 8.43 +/- 0.11, respectively, an increase in the pKa by 1.41 units, which conforms with the previous prediction. These results provide direct experimental proof of the redox-linked ionization of this residue and provides further evidence of the crucial role of electrostatic interactions, in this case, in the stabilization of the flavin hydroquinone anion. This phenomenon may represent a general mechanism in the modulation of the reduction potential of the flavin cofactor within flavoenzymes in which ionizable groups such as histidine in the active center change ionization states during the catalytic cycle.

Binding Sites↗