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At least 847 records · Page 47Linked to original sources
PubMed1996

Redox-linked ionization of sulredoxin, an archaeal Rieske-type [2Fe-2S] protein from Sulfolobus sp. strain 7.

"Sulredoxin" of Sulfolobus sp. strain 7 is an archaeal soluble Rieske-type [2Fe-2S] protein and was initially characterized by several spectroscopic techniques (Iwasaki, T., Isogai, T., Iizuka, T. , and Oshima, T. (1995) J. Bacteriol. 177, 2576-2582). It appears to have tightly linked ionization affecting the redox properties of the protein, which is characteristic of the Rieske FeS proteins found as part of the respiratory chain. Sulredoxin had an Em(low pH) value of +188 +/- 9 mV, and the slope of pH dependence of the midpoint redox potential indicated two ionization equilibria in the oxidized form with pKa(ox1) of 6.23 +/- 0.22 and pKa(ox2) of 8.57 +/- 0.20. The absorption, CD, and resonance Raman spectra of oxidized sulredoxin are consistent with the proposed St2FeSb2Fe[N(His)]t2 core structure, and deprotonation of one of the two putative coordinated histidine imidazoles, having the pKa(ox2) of 8.57 +/- 0.20, causes a decrease in the midpoint redox potential, the change in the optical and CD spectra, and the appearance of a new Raman transition at 278 cm-1, without major structural rearrangement of the [2Fe-2S] cluster as well as the overall protein conformation. The redox-linked ionization of sulredoxin is also contributed by local changes involving another ionizable group having the pKa(ox1) of 6.23 +/- 0. 22, which is probably attributed to a certain positively charged amino acid residue that may not be a ligand by itself but located very close to the cluster. We suggest that sulredoxin provides a new tractable model of the membrane-bound homologue of the respiratory chain, the Rieske FeS proteins of the cytochrome bc1-b6f complexes.

Circular Dichroism↗
PubMed2004

Inorganic salts influence IAA ionization and adventitious rhizogenesis in Pongamia pinnata.

The basal cut end of coppice shoot cuttings of Pongamia pinnata was treated for 24 h with 0 (water treated control) or 5.0 mmol/L of KMnO4, KCI, and KH2PO4 or 2.5 mmol/L of K2HPO4 and K2SO4. Inorganic salts of P, S, Cl and Mn significantly influenced IAA ionization and adventitious rhizogenesis. P and S salts had lower IAA ionization potential, but more pronounced effect on adventitious rhizogenesis than Cl and Mn salts. The linear regression analysis also established negative correlations between salt induced IAA ionization with various characteristics of adventitious rhizogenesis such as sprouting (r = -0.83, p < 0.05), rooting (r = -0.82, p < 0.05), root number (r = -0.95, p < 0.01), and root length (r = -0.80, p < 0.1). The implication of IAA ionization in adventitious rhizogenesis has been discussed and the possible role of inorganic salts therein suggested.

Ions↗
PubMed1996

Serum ionized magnesium and other electrolytes in the antenatal period of human pregnancy.

OBJECTIVE: To determine: 1) the concentrations and fractions of serum ionized magnesium (IMg2+) in normal antenatal patients and 2) whether they are altered by concentrations of other cations and serum proteins. DESIGN: A cross sectional study design. SETTING: An urban community hospital obstetrics clinic. SUBJECTS: 144 normal antenatal patients divided into four gestational age groups: (1) 25 at 6 to 12 weeks, (2) 55 at 13 to 20 weeks, (3) 37 at 21 to 27 weeks, and (4) 27 at 28 to 38 weeks. INTERVENTIONS: Utilizing ion selective electrodes, we determined concentrations and fractions of ionized magnesium, concentrations of ionized calcium, sodium, and potassium, and the pH level in the venous serum of the patients. Total magnesium (TMg), total calcium, total protein, albumin, and inorganic phosphorus were measured. MEASURES OF OUTCOME: The mean concentrations and fractions were compared between the groups. Correlations between concentrations or fractions of Mg and concentrations of the other cations or proteins were determined. RESULTS: All values are means+/-SD. IMg2+ concentrations are 0.53+/-0.03 mmol/L in the first trimester and are lowest (0.49+/-0.05 mmol/L, p<0.001) by the third trimester. The percent of ionized magnesium remains at approximately 66% in each antenatal group. Although mean Mg concentrations fall with advancing gestational age, the main determinant of the IMg2+ concentration in an individual patient is her TMg concentration. CONCLUSIONS: IMg2+ concentrations and fractions remain within a very narrow range during pregnancy and are minimally affected by physiologic hemodilution. We hypothesize that mobilization of intracellular or bone stores of magnesium helps maintain serum concentrations, thus placing a stress on magnesium balance.

Blood Proteins↗
PubMed2001

Increased body weight in C57BL/6 female mice after exposure to ionizing radiation or 60Hz magnetic fields.

PURPOSE: The purpose of this investigation was to determine whether early treatment with ionizing radiation and/or chronic magnetic field (MF) exposure affected body weight in female mice. MATERIALS AND METHODS: Weanling C57BL/6 female mice were irradiated with four equal weekly cobalt-60 exposures (total cumulative doses: 3.0, 4.0, 5.1Gy) and/or received chronic lifetime exposure to 1.4 mT 60 Hz circularly polarized MF or ambient MF. The body weights of 2280 mice were recorded at 35 age intervals, and analysis of variance was used to compare the mean differences from baseline weights between treatment groups and sham-exposed controls. RESULTS: A highly statistically significant effect of ionizing radiation on body weight was observed at 28 age intervals (p < or = 0.001), and for MF exposure at 10 age intervals (p < or = 0.001). During the young adult growth phase, mice exposed only to MF exhibited < or =0.5 g greater weight gain relative to sham-exposed controls (p = 0.0001). The effect of ionizing radiation alone was inversely related to dose, with the largest weight increases observed in all of the irradiated groups after 9-12 months (p = 0.0001). CONCLUSIONS: Treatment with split-dose ionizing radiation at an early age and chronic exposure to a residential power frequency MF were found to produce small but significant increases in body weight.

Animals↗
PubMed2006

Minor contribution of direct ionization to DNA base damage inducedby heavy ions.

PURPOSE: The deleterious processes triggered by heavy ions on DNA were studied through the determination of the yield of a series of oxidized bases. Emphasis was placed on the estimation of the respective contribution of direct ionization and indirect effects, mostly by comparison with low linear energy transfer (LET) gamma-rays. MATERIAL AND METHODS: DNA samples and human monocytes were exposed either to gamma-rays emitted by a (60)Co source or to (12)C(6+) or (36)Ar(18+) ions. The levels of thymidine and 2'-deoxyguanosine oxidation products were determined by liquid chromatography coupled to tandem mass spectrometry subsequently to DNA digestion into nucleosides. RESULTS: The yields of thymidine lesions were similar to those of 8-oxo-7,8-dihydro-2'-deoxyguanosine within isolated DNA exposed either to gamma-rays or argon ions. Addition of spermine and Tris aimed at minimizing the indirect effect modified this ratio to the same extent with both types of radiation. In cells, the level of radiation-induced base damage was found to be correlated with the radiolytic yield of degrees OH that depends on the LET of the particle. In addition, radiation-induced thymidine and 2'-deoxyguanosine lesions were produced in similar amounts. In contrast, oxidation of 2'-deoxyguanosine was the main process when ionization was triggered in cellular DNA by ultraviolet laser-induced biphotonic processes. CONCLUSIONS: Predominant oxidation of 2'-deoxyguanosine is expected to be the hallmark of direct DNA ionization. The observation that thymidine and 2'-deoxyguanosine are equally damaged rules out a major contribution of the direct ionization in radiation-induced base damage to both isolated and cellular DNA by heavy ions. Dependence of the yield of lesions on the LET provides further support for this conclusion.

DNA↗
PubMed1998

Cytogenetic signature for ionizing radiation.

A stable, easily measurable biological 'signature' for past exposure to densely ionizing radiation would be of significant value to estimate environmental radiation risk. Defined here, the S-ratio is the ratio of complete to incomplete chromosome translocations. It constitutes a clastogenic signature that appears to be stable over time, independent of dose, and varies inversely with the relative biological effectiveness (RBE) of the radiation. In vitro measurements resulted in a ratio of approximately 2 for densely ionizing radiation (56Fe and 12C ions) in contrast to a value of approximately 10 for sparsely ionizing radiation (X- and gamma-rays). The measured ratio was approximately 2 for bleomycin and benzene. Such a distinctive clastogenic signature should facilitate better estimates of neutron dose for A-bomb survivors, as well as a causal connection between early exposure to densely ionizing radiation and late development of cancer.

Animals↗
PubMed1999

Ionizing radiation and the activation of caspase-8 in highly apoptosis-sensitive lymphoma cells.

PURPOSE: Ionizing radiation induces apoptosis in human lymphoma cells. However, the participating molecules and their exact order is unknown. Caspases are reported as essential cysteine proteases required for the activation and execution of programmed cell death. The activator caspase-8 is a key component of the CD95/Fas/APO-1 death receptor-triggered apoptosis pathway. Since contributing molecules for radiation-induced apoptosis and their exact order have not been analyzed in greater detail, the involvement of caspase-8 for radiation-induced apoptosis in human lymphoma cell lines was studied. MATERIALS AND METHODS: Apoptosis induction by CD95 stimulation and ionizing radiation was analyzed in eight different cell lines. In parallel, Western blotting tested activation of caspase-8. RESULTS: Activation of caspase-8 by ionizing radiation occurred in five cell lines and was associated with high apoptosis sensitivity. Caspase-8 activation and apoptosis was detectable in cells resistant to CD95 stimulation, so suggesting separate pathways for CD95 and radiation-induced caspase-8 activation. CONCLUSION: The activator caspase-8 is activated during radiation-induced cell death and, in some cases, ionizing radiation induces caspase-8 independently of the CD95 system.

Apoptosis↗
PubMed2000

The mechanism of detection of air pollution by an ionization chamber.

The mechanism of detection of chemical vapors in air by an ionization chamber supplied by DC and AC voltage has been described. The theoretical explanation is based on numerical solutions of the differential equations of the cylindrical ionization chamber. The current of the ionization chamber operating in the AC regime has two components: a conductive component, caused by the ions drifts, and a capacitive component, caused by the distortion of the electric field. The ionization chamber operating in the DC regime has only the first component; hence the AC supplied chamber has larger response than the DC supplied chamber.

Air Pollutants↗
PubMed2002

Ionized serum calcium levels during acute renal failure: intermittent hemodialysis vs. Continuous hemodiafiltration.

BACKGROUND: Achieving "adequacy of dialysis" includes the maintenance of normal serum ionized calcium concentrations and is an important therapeutic goal in the treatment of acute renal failure (ARF). It is unknown whether this goal is best achieved with intermittent or continuous renal replacement therapy. METHODS: We compared the effects of continuous veno-venous hemodiafiltration (CVVHDF) and intermittent hemodialysis (IHD) on serum ionized calcium concentrations using daily morning blood tests in 88 consecutive intensive care patients of which half were treated with IHD and half with CRRT. RESULTS: Mean patient age was 54 +/- 14 years for IHD and 60 +/- 14 years for CVVHDF (NS). However, patients who received CVVHDF were significantly more critically ill (mean APACHE II scores: 24.4 +/- 5.1 for IHD vs. 29.2 +/- 5.7 for CVVHDF, p < 0.003). Before treatment, the mean ionized calcium concentration was 1.177 +/- 0.03 mmol/l for IHD and 1.172 +/- 0.04 mmol/l for CVVHDF (NS), with abnormal values in 51.6% of IHD patients and in 68% of CVVHDF patients (NS). During treatment, hypocalcemia was significantly more common among CVVHDF patients (24.5% vs. 14.9%; p < 0.011) while hypercalcemia was more frequent during IHD (36.1% vs. 25.6%; p < 0.019). CONCLUSIONS: Abnormal serum ionized calcium concentrations are frequent in ARF patients before and during renal replacement. Once dialytic therapy is applied, CVVHDF is more likely to lower serum calcium concentrations, while IHD is more likely to induce hypercalcemia. Appreciation of these different biochemical effects may assist clinicians in adjusting dialytic therapy in selected patients.

Acute Kidney Injury↗
PubMed1990

Ionized carbon in side-illuminated molecular clouds.

We have observed the 2P3/2-2P1/2 fine-structure line of C II at 1900 GHz in five sources with ionization fronts nearly perpendicular to the plane of the sky. The LSR velocity of the C II emission is generally in good agreement with that observed for molecular species such as CO. However, the observed line widths of 3-14 km s-1 are typically wider than those of molecular lines and often show rapid spatial variations in the regions observed. In some sources this may indicate that part of the C II emanates from an ionized gas component, while for others it suggests an association between C II emission and an outflow. The C II brightness temperatures are typically equal to or slighty higher than the dust temperature at all locations observed. In the optically thin approximation, C II excitation temperatures are > or = 100 K and column densities are < or = 10(18) cm-2 for all sources except M17, which has a more intense and complicated line profile with a larger spatial extent than any other source observed. The quoted column density estimates derived in the optically thin limit appear to be somewhat lower than those predicted by models of photodissociation regions for sources with a side-illuminated geometry, but uncertainties in the UV flux and geometry of the ionization front preclude a definitive comparison. The estimated column densities would be higher if the C II emission were somewhat optically thick, in which case the ionized carbon would be more in equilibrium with the dust at temperatures lower than predicted by current models.

Astronomical Phenomena↗
PubMed1993

Theoretical infrared spectra of some model polycyclic aromatic hydrocarbons: effect of ionization.

In order to test the hypothesis of ionized polycyclic aromatic hydrocarbons (PAHs) as possible carriers of the UIR bands, we realized a computational exploration on selected PAHs of small dimension in order to identify which changes ionization would induce on their IR spectra. In this study we performed ab initio calculations of the spectra of neutral and positively ionized naphthalene, anthracene, and pyrene. The results are significantly important. The frequencies in the cations are slightly shifted with respect to the neutral species, but no general conclusion can be reached from the three molecules considered. By contrast, the relative intensities of most vibrations are strongly affected by ionization, leading to a much better agreement between the calculated CH/CC vibration intensity ratios and those deduced from observations.

Anthracenes↗
PubMed1995

Experimental determination of the beam quality dependence factors, kQ, for ionization chambers used in photon and electron dosimetry.

Dosimetry in radiotherapy with ionization chambers calibrated in 60Co gamma beams in terms of absorbed dose to water, DW, can be performed if a factor conventionally denoted as kQ is known. The factor kQ depends on the beam quality and the chamber characteristics. Calculated values of the kQ factors for many types of ionization chamber have been recently published. In this work the experimental determination of the kQ factors for various ionization chambers was performed for 6 MV and 15 MV photon beams and for a 14 MeV electron beam. The kQ factors were determined by a procedure based on relative measurements performed with the ionization chamber and ferrous sulphate solution in 60Co gamma radiation and accelerator beams, respectively. The experimental kQ values are compared with the calculated values so far published. Theoretical and experimental kQ values are in fairly good agreement. The uncertainty in the experimental kQ factors determined in this work is less than about 1%, that is, appreciably smaller than the uncertainty of about 1.5% reported for the calculated values.

Cobalt Radioisotopes↗
PubMed1998

On the use of unshielded cables in ionization chamber dosimetry for total-skin electron therapy.

The dosimetry of total-skin electron therapy (TSET) usually requires ionization chamber measurements in a large electron beam (up to 120 cm x 200 cm). Exposing the chamber's electric cable, its connector and part of the extension cable to the large electron beam will introduce unwanted electronic signals that may lead to inaccurate dosimetry results. While the best strategy to minimize the cable-induced electronic signal is to shield the cables and its connector from the primary electrons, as has been recommended by the AAPM Task Group Report 23 on TSET, cables without additional shielding are often used in TSET dosimetry measurements for logistic reasons, for example when an automatic scanning dosimetry is used. This paper systematically investigates the consequences and the acceptability of using an unshielded cable in ionization chamber dosimetry in a large TSET electron beam. In this paper, we separate cable-induced signals into two types. The type-I signal includes all charges induced which do not change sign upon switching the chamber polarity, and type II includes all those that do. The type-I signal is easily cancelled by the polarity averaging method. The type-II cable-induced signal is independent of the depth of the chamber in a phantom and its magnitude relative to the true signal determines the acceptability of a cable for use under unshielded conditions. Three different cables were evaluated in two different TSET beams in this investigation. For dosimetry near the depth of maximum buildup, the cable-induced dosimetry error was found to be less than 0.2% when the two-polarity averaging technique was applied. At greater depths, the relative dosimetry error was found to increase at a rate approximately equal to the inverse of the electron depth dose. Since the application of the two-polarity averaging technique requires a constant-irradiation condition, it was demonstrated than an additional error of up to 4% could be introduced if the unshielded cable's spatial configuration were altered during the two-polarity measurements. This suggests that automatic scanning systems with unshielded cables should not be used in TSET ionization chamber dosimetry. However, the data did show that an unshielded cable may be used in TSET ionization chamber dosimetry if the size of cable-induced error in a given TSET beam is pre-evaluated and the measurement is carefully conducted. When such an evaluation has not been performed, additional shielding should be applied to the cable being used, making measurements at multiple points difficult.

Biophysical Phenomena↗
PubMed2005

A new extended-length parallel-plate ionization chamber.

A special parallel-plate ionization chamber was developed. The motivation for the construction of this new chamber was mainly to fulfil the need of a reference system for computed tomography standard beams in the Calibration Laboratory of IPEN. However, the chamber was tested also in standard radiation beams of mammography and conventional diagnostic radiology. The chamber was manufactured at the institute workshop, as simply and cheaply as possible. Its design differs from the common ionization chambers used in dosimetric procedures of computed tomography equipment, because it is a parallel-plate chamber instead of a cylindrical chamber. However, its dimensions and sensitive volume are very similar to those of a commercial pencil ionization chamber. The new ionization chamber was submitted to several characterization and quality control tests, showing its very good performance.

Biophysics↗
PubMed1990

DOCA-salt treatment decreases serum total calcium but not ionized calcium concentrations in rats.

We examined whether or not DOCA-salt treatment to rats would decrease serum ionized calcium concentrations in relation to the enhanced hypotensive response to the calcium antagonist nifedipine. DOCA-salt treatment increased blood pressure and enhanced the hypotensive effects of nifedipine. Serum total calcium and albumin levels were clearly reduced, but the ionized fraction of calcium was not altered by treatment with DOCA-salt for 4 weeks. The total serum calcium concentration, but not the ionized calcium, significantly correlated with serum albumin in DOCA-salt rats. A reduction in serum ionized calcium may therefore not be induced by DOCA-salt treatment and may not be related to the enhanced depressor response to nifedipine.

Animals↗
PubMed1993

Ionized magnesium and calcium levels in umbilical cord serum of pregnant women with transient hypertension during labor.

Using a new ion selective electrode (ISE) to measure ionized magnesium (IMg2+), we compared levels of IMg2+ with total magnesium (TMg) and serum ionized calcium levels (ICa2+) in umbilical arterial and venous serum of 13 parturients who developed transient hypertension in labor with levels in 38 who remained normotensive. Ionized, but not total magnesium levels were significantly lower in the umbilical veins of the hypertensive compared to the normotensive subjects (0.46 +/- 0.01 v 0.51 +/- 0.01 mmol/L), and these were at least 15% lower than maternal levels found in nonpregnant women (0.60 +/- 0.005 mmol/L, P < .001). If umbilical vein samples reflect maternal levels as well, then these results suggest that lower IMg2+ levels may play a role in the development of transient hypertension in labor, and the potential utility of an ion selective electrode for ionized magnesium in the diagnosis of subtle magnesium deficient states.

Calcium↗
PubMed1997

Dietary skim milk powder increases ionized calcium in the small intestine of piglets compared to dietary defatted soybean flour.

Calcium distribution was studied in the small intestine of piglets fed skim milk powder (SMP) or defatted soybean flour (DSF ) to investigate the relationship between calcium availability and its forms. Ionized calcium in duodenal and ileal digesta was measured with a selective calcium electrode that was not affected by changes in pH or sodium, potassium and magnesium concentrations, which simulated the liquid phases of digesta. Eight piglets were fed DSF-based diet or SMP-based diet for 30 d, and duodenal and ileal digesta were collected. Soluble calcium concentrations in the ileum were higher in the SMP-fed group than in the DSF-fed group. The proportion of soluble calcium in higher-molecular-weight fraction (MW > 3000) was significantly greater in the ileum than in the duodenum of the SMP group, but did not differ between these intestinal segments within the DSF group. This proportion was significantly higher in the ileum of the SMP-fed group than in that of the DSF-fed group. In the ileum, ionized calcium concentration was significantly greater in the SMP-fed group than in the DSF-fed group. These results suggest that the increase of calcium in the higher-molecular-weight fraction raises soluble calcium concentration and changes the distribution of calcium in the ileum of the SMP-fed group. The complexes of calcium with higher-molecular-weight ligands may be easily exchangeable with ionized calcium, and the increase in these calcium complexes may consequently enhance the recruitment of ionized calcium, which then can be absorbed.

Animals↗
PubMed1991

Numerical method to analyze pH-profile from initial velocity data and semi-empirical procedure to identify catalytic residues of enzymes using pK and heat of ionization.

A numerical computing method to estimate pK and heat of ionization directly from initial velocity data was developed for systematic analysis of rate parameters. Values of rate and thermodynamic parameters were determined together with standard deviations, without using Arrhenius and van't Hoff plots. Distributions of pK and heat of ionization of small-molecular derivatives of aliphatic carboxylates, imidazoles, thiols, and aliphatic amines as possible models for catalytic residues of enzymes were analyzed from a thermodynamic point of view. Each group was classified in a parallelogram without overlapping, except for a part of the imidazole and thiol groups. It was shown that values of pK and heat of ionization of carboxylates and histidine residues involved in the catalytic activity of enzymes determined from pH-profile experiments can be classified into similar, though somewhat extended, areas to those of the corresponding small-molecular derivatives. Identification of catalytic residues using values of pK and heat of ionization is proved to be a reliable method when the procedure is properly used.

Computer Simulation↗