PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Chlorates”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53Linked to original sources
PubMed1999

Association of bacteriochlorophyll a with the CsmA protein in chlorosomes of the photosynthetic green filamentous bacterium Chloroflexus aurantiacus.

The protein assumed to be associated with bacteriochlorophyll (BChl) a in chlorosomes from the photosynthetic green filamentous bacterium Chloroflexus aurantiacus was investigated by alkaline treatment, proteolytic digestion and a new treatment using 1-hexanol, sodium cholate and Triton X-100. Upon alkaline treatment, only the 5.7 kDa CsmA protein was removed from the chlorosomes among six proteins detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis, concomitantly with the disappearance of BChl a absorption at 795 nm. Trypsin treatment removed two proteins with molecular masses of 11 and 18 kDa (CsmN and CmsM), whereas the spectral properties of BChl a and BChl c were not changed. By the new hexanol-detergent (HD) treatment, most BChl c and all of the detected proteins except CsmA were removed from the chlorosomes without changing the BChl a spectral properties. Subsequent proteinase K treatment of these HD-treated chlorosomes caused digestion of CsmA and a simultaneous decrease of the BChl a absorption band. Based on these results, we suggest that CsmA is associated with BChl a in the chlorosomes. This suggestion was supported by the measured stoichiometric ratio of BChl a to CsmA in isolated chlorosomes, which was estimated to be between 1.2 and 2.7 by amino acid analysis of the SDS-PAGE-resolved protein bands.

Amino Acids↗
PubMed2001

Enhancement of gene delivery by an analogue of alpha-MSH in a receptor-independent fashion.

In order to transfect melanoma specifically by receptor-mediated endocytosis we prepared dioctadecyl aminoglycylspermine (lipospermine)--DNA complexes with [Nle(4),D-Phe(7)]-alpha-MSH(4--10), a pseudo-peptide analogue of alpha-melanocyte stimulating hormone (alpha-MSH) linked to a thiol-reactive phospholipid. With these complexes we obtained an up to 70-fold increase of transfection with B16-F1 melanoma cells. However when B16-G4F, an alpha-MSH receptor negative melanoma cell line was transfected, an up to 700-fold increased transfection efficiency was observed. The peptide hormone analogue was equally efficient when it was only mixed with lipospermine--DNA complexes without covalent coupling. In addition to melanoma cells we also obtained up to 30-fold increased transfection with BN cells (embryonic liver cells). Our data show that an alpha-MSH analogue increased transfection independently of the MSH receptor expression but reaches efficiencies approaching those obtained with peptides derived from viral fusion proteins. The absence of targeting of constructs containing [Nle(4),D-Phe(7)]-alpha-MSH(4-10) can probably be attributed due to the relatively modest number of MSH receptors at the surface of melanoma. We suggest, however, that the peptide hormone analogue used in this study has membrane-active properties and could be of interest as helper agent to enhance non-viral gene delivery presumably by endosomal-destabilizing properties.

Affinity Labels↗
PubMed1998

Differences in the electrophysiological response to I- and the inhibitory anions SCN- and ClO-4, studied in FRTL-5 cells.

The electrophysiological properties of the Na+/I- symporter (NIS) were examined in a cloned rat thyroid cell line (FRTL-5) using the whole-cell patch-clamp technique. When the holding potential was between -40 mV and -80 mV, 1 mM NaI and NaSCN induced an immediate inward current which was greater with SCN- than with I-. The reversal potential for I- and SCN- induced membrane currents was +50 mV. This is close to the value of +55 mV calculated by the Nernst equation for Na+. These results are consistent with I- and SCN- translocation via the NIS that is energized by the electrochemical gradient of Na+ and coupled to the transport of two or more Na+. There was no change in the membrane current recording with ClO-4 indicating that ClO-4 was either not transported into the cell, or the translocation was electroneutral. ClO-4 addition, however, did reverse the inward currents induced by I- or SCN-. These effects of I-, SCN- and ClO-4 on membrane currents reflect endogenous NIS activity since the responses duplicated those seen in CHO cells transfected with NIS. There were additional currents elicited by SCN- in FRTL-5 cells under certain conditions. For example at holding potentials of 0 and +30 mV, 1 mM SCN- produced an increasingly greater outward current. This outward current was transient. In addition, when SCN- was washed off the cells a transient inward current was detected. Unlike SCN-, 1-10 mM I- had no observable effect on the membrane current at holding potentials of 0 and +30 mV. The results indicate FRTL-5 cells may have a specific SCN- translocation system in addition to the SCN- translocation by the I- porter. Differences demonstrated in current response may explain some of the complicated influx and efflux properties of I-, SCN- and ClO-4 in thyroid cells.

Animals↗
PubMed2000

Anion modulation of calcium current voltage dependence and amplitude in salamander rods.

Hofmeister anions were used to investigate the ability of Cl(-) replacement to produce inhibition and a hyperpolarizing activation shift in L-type Ca(2+) currents (I(Ca)) of rod photoreceptors. Inhibition of I(Ca) largely followed the Hofmeister sequence: Cl(-)=Br(-)<NO(-)(3)<I(-)<ClO(-)(4) (ClO(-)(4) caused the greatest suppression). Anion-induced hyperpolarizing activation shifts also followed the Hofmeister sequence: Cl(-)<Br(-)<NO(-)(3)<I(-)<ClO(-)(4) (ClO(-)(4) caused the largest shift). Agreement with the Hofmeister sequence suggests that these effects are due to anion interactions at the membrane surface. Hofmeister anions also caused similar hyperpolarizing shifts in the voltage dependence of inwardly rectifying cation currents (I(h)) and outward K(+) currents (I(K)) consistent with the hypothesis that hyperpolarizing shifts arise from anion effects on membrane surface potential. Sulfate and phosphate inhibited rod I(Ca) and phosphate caused a significant leftward activation shift suggesting these anions are strongly adsorbed to the membrane. Because of the overlap between the physiological voltage range and the lower part of the I(Ca) activation curve, anion effects on amplitude and activation may influence synaptic transmission at the first retinal synapse.

Animals↗
PubMed2003

Macromolecular and solution properties of Cepacian: the exopolysaccharide produced by a strain of Burkholderia cepacia isolated from a cystic fibrosis patient.

Light scattering and viscosity measurements were carried out on the previously chemically characterised exopolysaccharide produced by a strain of Burkholderia cepacia isolated from a cystic fibrosis patient. The same exopolysaccharide was also produced by other clinical strains in different laboratories. Therefore, the name Cepacian is now proposed for this exopolysaccharide. Experiments performed as a function of the ionic strength on the native polymer revealed a change in the overall shape of the polymer at low ionic strength. This behaviour was absent in the de-acetylated sample. Potentiometric titrations and light scattering experiments carried out on the acidic form of the native polymer revealed the formation of macromolecular aggregates with a stoichiometry n and 2n stabilised by interactions involving the uronic acid residues.

Acetates↗
PubMed1999

Tyrosine sulfation of the amino terminus of CCR5 facilitates HIV-1 entry.

Chemokine receptors and related seven-transmembrane-segment (7TMS) receptors serve as coreceptors for entry of human and simian immunodeficiency viruses (HIV-1, HIV-2, and SIV) into target cells. Each of these otherwise diverse coreceptors contains an N-terminal region that is acidic and tyrosine rich. Here, we show that the chemokine receptor CCR5, a principal HIV-1 coreceptor, is posttranslationally modified by O-linked glycosylation and by sulfation of its N-terminal tyrosines. Sulfated tyrosines contribute to the binding of CCR5 to MIP-1 alpha, MIP-1 beta, and HIV-1 gp120/CD4 complexes and to the ability of HIV-1 to enter cells expressing CCR5 and CD4. CXCR4, another important HIV-1 coreceptor, is also sulfated. Tyrosine sulfation may contribute to the natural function of many 7TMS receptors and may be a modification common to primate immunodeficiency virus coreceptors.

Amino Acid Sequence↗
PubMed2000

Alcohol-induced versus anion-induced states of alpha-chymotrypsinogen A at low pH.

Characterization of conformational transition and folding intermediates is central to the study of protein folding. We studied the effect of various alcohols (trifluoroethanol (TFE), butanol, propanol, ethanol and methanol) and salts (K(3)FeCN(6), Na(2)SO(4), KClO(4) and KCl) on the acid-induced state of alpha-chymotrypsinogen A, a predominantly beta-sheet protein, at pH 2.0 by near-UV circular dichroism (CD), far-UV CD and 1-anilinonaphthalene-8-sulfonic acid (ANS) fluorescence measurements. Addition of alcohols led to an increase in ellipticity value at 222 nm indicating the formation of alpha-helical structure. The order of effectiveness of alcohols was shown to be TFE>butanol>propanol>ethanol>methanol. ANS fluorescence data showed a decrease in fluorescence intensity on alcohol addition, suggesting burial of hydrophobic patches. The near-UV CD spectra showed disruption of tertiary structure on alcohol addition. No change in ellipticity was observed on addition of salts at pH 2.0, whereas in the presence of 2 M urea, salts were found to induce a molten globule-like state as evident from the increases in ellipticity at 222 nm and ANS fluorescence indicating exposure of hydrophobic regions of the protein. The effectiveness in inducing the molten globule-like state, i.e. both increase in ellipticity at 222 nm and increase in ANS fluorescence, followed the order K(3)FeCN(6)>Na(2)SO(4)>KClO(4)>KCl. The loss of signal in the near-UV CD spectrum on addition of alcohols indicating disordering of tertiary structure results suggested that the decrease in ANS fluorescence intensity may be attributed to the unfolding of the ANS binding sites. The results imply that the alcohol-induced state had characteristics of an unfolded structure and lies between the molten globule and the unfolded state. Characterization of such partially folded states has important implications for protein folding.

1-Propanol↗
PubMed2002

The effect of anions on azide binding to myoglobin: an unusual functional modulation.

The effect of increasing concentrations of several anions on the azide (N(-)(3)) binding properties of sperm whale and horse ferric myoglobin has been studied. Surprisingly, a number of anions may act as heterotropic effectors, decreasing the affinity of myoglobins for N(-)(3), in the following order: ClO(-)(4)=I(-)>Br(-)>Cl(-) and SO(2-)(4), which mirrors the increase in their charge density. The largest effects were measured using ClO(-)(4) and I(-), which produce a 4-fold and 8-fold reduction of the N(-)(3) binding affinity in horse and sperm whale myoglobins, respectively. A dissociation equilibrium constant (K(d)) ranging from 150 to 250 mM was estimated for ClO(-)(4) and I(-) binding to myoglobins. In order to analyse the molecular mechanism producing the reduction of the N(-)(3) binding affinity to ferric myoglobin, the potential anionic binding sites within ferric myoglobin were investigated by a molecular modelling study using the program Grid. Analysis of the theoretical results suggests two particularly favourable binding sites: the first, next to the distal side of the haem, whose occupancy might alter the electrostatic potential surrounding the bound N(-)(3); the second, involving residues of helices B and G which are far from the haem iron atom, thus implying a long range effect on the bound N(-)(3). Based on the evidence that no significant conformational changes are found in the three-dimensional structures of N(-)(3)-free and N(-)(3)-bound myoglobin and on previous results on N(-)(3) binding to ferric myoglobin mutants in CD3 positions, we favour the first hypothesis, suggesting that the functional heterotropic modulation of monomeric myoglobin is mainly depending on a decrease of the positive charge density induced by the binding of anions to the haem distal side.

Allosteric Regulation↗
PubMed1999

Cell-surface heparan sulfate facilitates human immunodeficiency virus Type 1 entry into some cell lines but not primary lymphocytes.

Many viruses have evolved to exploit cell-surface glycosaminoglycans (GAG), particularly heparan sulfate, to facilitate their attachment and infection of host cells. Here, the case for the involvement of heparan sulfate GAG in cellular infection by human immunodeficiency virus Type 1 (HIV-1) compared with herpes simplex virus Type 1 (HSV-1) is re-examined. It is shown that HIV-1 infection is facilitated by heparan sulfate GAG in only one of three highly permissive cell lines tested, whereas HSV-1 infection is facilitated to varying extents in all three. To evaluate the physiological relevance of these findings, primary peripheral blood lymphocytes (PBL), the physiological host for HIV-1, were examined. It was found that treatment of PBL with heparitinase, to remove any traces of heparan sulfate GAG, did not alter their sensitivity to infection by either lymphocyte-tropic, X4-type strain HIV-1IIIB, nor the monocyte-tropic, R5-type strain, HIV-1Ba-L. It is concluded that heparan sulfate GAG has little physiological role in the infection of lymphocytes by HIV-1 and that evidence derived from studies on immortalized cell lines suggesting a significant role must be interpreted with caution.

Cell Line↗
PubMed1976

Increased nitrate reductase A activity as a sign of membrane alteration in early blocked asporogenous mutants of Bacillus subtilis.

Nitrate reductase (Nar) activity, and its regulation, have been studied in B. subtilis and Spo0 mutants derived from it. The mutants are blocked at the stage zero of sporulation. The only Nar detected was the membrane-bound Nar A, which has been solubilized and purified. The enzyme itself, and its regulation, seem to be the same in Spo+ and Spo0 strains. Under all conditions tested, however, the mutants were hyperproducers of Nar A. Whether produced by a Spo+ or a Spo0 strain, the purified enzyme has the same Km on nitrate, and the same heat inactivation kinetics. In situ in membrane vesicles of a Spo+ strain, it displays the same Km and its thermoinactivation is exponential. In mutant vesicles, however, two Km's are observed, one normal and one five times higher, and thermoinactivation follows an initial period of activation. The higher Km disappears after heat activation. The Spo0 mutation studied seems to result in a modification of the membrane, such that insertion of Nar A in the modified membrane confers to the enzyme new allotopic properties. Additional and abnormal enzyme-binding sites may be created as a result of the mutation and these may be normalized during heat activation.

Bacillus subtilis↗
PubMed1997

Double quantum coherence of quadrupolar I = 1 nuclei: 14N in NH4ClO4.

We have calculated optimal conditions for observing the double quantum coherence of quadrupolar nuclei I = 1 in single crystals and powders after the two and three pulse sequences (theta1)x-tau1-(theta2)alpha-tau2 [-(theta3)beta-tau3] Here alpha and beta are the phase-cycling angles, which were incremented properly to select the desired coherence transfer pathways. Experiments for double quantum excitation and detection were performed on the single crystal and powder samples of NH4ClO4. Because of a fast decay of the signal from the powder after the two-pulse sequence, we employed the third pulse to produce an echo related to the double quantum coherence.

Chlorates↗
PubMed2003

Beta-cyclodextrin-based ferrocene-imprinted gold electrodes.

A new stepwise self-assembly procedure is described for the preparation of functional cyclodextrin-modified electrodes. The approach is based on the formation of alkanethiol/lipoylamide-beta-cyclodextrin monolayers with the thiol component responsible for blocking of the electrode surface and lipoylamide-beta-cyclodextrin molecules-for controlled opening of the access of the electroactive probe to the electrode. Functionalization of the electrode is achieved by means of a new cyclodextrin derivative-mono(6-deoxy-6-lipoylamide)-per-2,3,6-O-acetyl-beta-cyclodextrin-prepared in the peracetyl form and deacetylated directly on the electrode surface following the cyclodextrin self-assembly. The progress of deacetylation was monitored by the MALDI MS technique. Deacetylation caused opening of the active sites toward solution probes. The response toward ferrocene was found to be highly improved when ferrocene was added to the solution following self-assembly of cyclodextrin but prior to the thiol self-assembly step (imprinting method). The proposed synthesis and sequential monolayer formation scheme lead to well-organized and stable modified electrode surfaces with improved sensitivity toward solution species compared to other procedures of electrode modification with the cyclodextrin derivatives.

Algorithms↗
PubMed2003

Unique holoenzyme dimers of the tetrameric enzyme Escherichia coli methylenetetrahydrofolate reductase: characterization of structural features associated with modulation of the enzyme's function.

Impaired functioning of methylenetetrahydrofolate reductase (MTHFR) can cause high levels of homocysteine in plasma or hyperhomocysteinemia, which is an independent risk factor for cardiovascular diseases and neural tube defects. We have studied in detail the effect of modulation of hydrophobic and electrostatic interactions of Escherichia coli MTHFR on its structure and function. Alterations in hydrophobic interactions of MTHFR, using urea, lead to dissociation of the native tetramer, resulting in stabilization of enzymatically active holoenzyme dimers followed by unfolding of the holoenzyme dimer to the denatured monomer along with dissociation of FAD from the enzyme. This is the first report of an enzymatically active dimer of E. coli MTHFR and suggests that the dimer rather than tetramer is the smallest functionally active unit of the enzyme. Furthermore, these results also demonstrate that dissociation of the FAD cofactor from the enzyme occurs only on unfolding of the dimer to denatured monomers. Modulation of electrostatic interactions, using NaCl, leads to dissociation of the native enzyme, resulting in stabilization of an enzymatically inactive partially unfolded holoenzyme dimer. Comparative analysis of loss of enzymatic activity and changes in structural features of MTHFR demonstrate a very good correlation between enhanced flexibility of the enzyme-bound FAD and loss of enzymatic activity, suggesting the importance of rigidity of the FAD cofactor in maintenance of the enzymatic activity of MTHFR.

Bacterial Proteins↗
PubMed2002

Photocatalytic reduction and recovery of copper by polyoxometalates.

A series of polyoxometalates PW12O40(3-), SiW12O40(4-), and P2Mo18O62(6-) have been used as photocatalysts for recovery of copper and production of fine metal particles. The process involves absorption of light by polyoxometalates, oxidation of an organic substrate, for instance, propan-2-ol as sacrificial reducing reagent, and reoxidation of the reduced polyoxometalates by Cu2+ ions, closing the photocatalytic cycle. Copper(II) ions are reduced to copper(I) and finally to zero-state particles in a 2-electron process, as also suggested by the half-order dependence. Increase of catalyst or propan-2-ol concentration, or both, accelerates the photodeposition of copper until a saturation value is reached. The method is operational at a wide range of copper concentrations varying from 3 to 1300 ppm, leading to very low final concentrations (<0.2 ppm). The presence of dioxygen suppresses the initiation of copper recovery, though the process is equally effective after dioxygen is consumed. The process is independent of pH within the range 0.3-5.0. Addition of ClO4-, NO3-, or CH3COO- has no effect on the removal of copper ions. Chloride ions retard the enhancement of copper precipitation through stabilization of copper(I). This homogeneous, polyoxometalate-based process exhibits some benefits in comparison with the semiconductor-based (heterogeneous) recovery of metals: The final zero-state metal particles are obtained in pure form. No separation from the catalyst is needed, and moreover, the process is catalytic as the photodeposited metal particulates do not hinder the photocatalytic action of polyoxometalate anions.

Acetates↗