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At least 289 records · Page 16Linked to original sources
PubMed1991

Identification of valine/leucine/isoleucine and threonine/alanine/glycine proton-spin systems of Escherichia coli adenylate kinase by selective deuteration and selective protonation.

Adenylate kinase from two types of Escherichia coli strains, a wild-type and a leucine-auxotrophic strain, was purified. On the one hand, growing the leucine-auxotrophic bacteria on a medium containing deuterated leucine yielded E. coli adenylate kinase with all leucine residues deuterated. On the other hand, by growing the wild-type bacteria on deuterated medium with phenylalanine, threonine and isoleucine present as protonated specimens, 80% randomly deuterated enzyme with protonated phenylalanine, threonine and isoleucine residues could be prepared. Use of these proteins enabled identification of the spin systems of these amino acid residues in the n.m.r. spectra of the protein.

Adenylate Kinase↗
PubMed2003

Effect of different proton pump inhibitors, differences in CYP2C19 genotype and antibiotic resistance on the eradication rate of Helicobacter pylori infection by a 1-week regimen of proton pump inhibitor, amoxicillin and clarithromycin.

AIM: To investigate the effect of different proton pump inhibitors, S-mephenytoin 4'-hydroxylase (CYP2C19) genotype and antibiotic susceptibility on the eradication rate of Helicobacter pylori. METHODS: One hundred and eighty-seven H. pylori-infected peptic ulcer patients were randomly treated with either rabeprazole (10 mg b.d.) or lansoprazole (30 mg b.d.) plus amoxicillin (750 mg b.d.) and clarithromycin (400 mg b.d.) for 1 week. The antibiotic susceptibility and CYP2C19 genotype (extensive or poor metabolizer) were investigated. RESULTS: The eradication rates in the rabeprazole-amoxicillin-clarithromycin (RAC) and lansoprazole-amoxicillin-clarithromycin (LAC) groups were 75% and 69%, respectively, on an intention-to-treat basis, and 80% and 75%, respectively, on a per protocol basis. The eradication rate for clarithromycin-resistant strains was significantly lower than that for clarithromycin-sensitive strains (24% vs. 86%, P < 0.05). For clarithromycin-sensitive strains in the LAC group, there was a tendency for a lower eradication rate in extensive than poor metabolizers. The eradication rate in extensive metabolizers in the RAC group tended to be higher than that in extensive metabolizers in the LAC group (89% vs. 78%, P = 0.079726). CONCLUSIONS: The success of the 1-week proton pump inhibitor-amoxicillin-clarithromycin regimen depends on the susceptibility of H. pylori to clarithromycin. Moreover, differences in CYP2C19 genotype influence the eradication rates of lansoprazole-based therapy, and the rabeprazole-based regimen has an advantage especially in extensive metabolizers.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed1988

13C NMR assignments of the protonated carbons of [d(TAGCGCTA)]2 by two-dimensional proton-detected heteronuclear correlation.

The resonances of the protonated carbons of [d(TAGCGCTA)]2 have been assigned by the two-dimensional proton-detected double-quantum heteronuclear correlation experiment [( 1H-13C]-DQCOSY). 13C-coupled and 13C-decoupled versions of the experiment were used. The assignment method is discussed in detail. The deoxyribose cross peaks segregate into five well-resolved regions, and the base cross peaks have distinct features that are helpful for assignments. The cross peaks from the 1H-13C pairs at the Cyd5, Ado2 and ThdCH3 base positions fall in separate regions of the spectrum from each other; they also are resolved from the closely spaced Ado8, Guo8, Cyd6 and Thd6. Additional parameters for distinction of the base signals are their differing J-coupling values and long-range coupling patterns.

Carbon Isotopes↗
PubMed1983

Proton NMR studies on the covalently linked RNA-DNA hybrid r(GCG)d(TATACGC). Assignment of proton resonances by application of the nuclear Overhauser effect.

Proton NMR spectra of a covalently linked self-complementary RNA X DNA hybrid, r(GCG)-d(TATACGC), are recorded in H2O and D2O. Imino proton resonances as well as the non-exchangeable base and H-1' resonances are unambiguously assigned by means of nuclear. Overhauser effect measurements. Additional information was obtained by 31P NMR and circular dichroism spectra. The RNA parts in the duplex attain full conformational purity and adopt the usual A-RNA conformation. The DNA residues opposite the RNA tract do not adopt an A-type structure completely. Their respective sugar rings still appear to possess a certain conformational freedom. The same holds true for the central d(-TATA-) sequence which forms a DNA X DNA duplex. There appears to be a structural break in this part: the first two residues, T(4) and A(5), are clearly influenced by the adjacent RNA structure, whereas residues T(6) and A(7) behave quite similar to what usually is found in DNA duplexes in aqueous solution.

Base Sequence↗
PubMed1984

Proton-coupled 15N NMR spectra of neutral and protonated ethenoadenosine and ethenocytidine.

The 15N chemical shifts and 15N, 1H spin coupling constants were determined in the title compounds using the INEPT pulse sequence and assigned with the aid of selective proton decoupling. The delta/15N/ and J/N, H/ values are discussed in terms of involvement of the imidazole ring created by ethenobridging in the electronic structure of the whole molecule. Both spectral parameters indicate that the diligant nitrogen in this ring is the primary site of protonation in these modified nucleosides. It is concluded that 15N NMR of nucleoside bases can be largely a complementary method to 1H and 13C NMR studies and, in addition, can serve as a direct probe for studies of nitrogen environment in oligomeric fragments of nucleic acids even at moderately strong magnetic fields due to the higher spectral dispersion compared with 1H and 13C NMR spectra.

Adenosine↗
PubMed1987

Selective catalysis of A.T base pair proton exchange in DNA complexes: imino proton NMR analysis.

Polyaromatic molecules with amino chain substituents, upon binding with DNA, selectively catalyze exchange of the A.T base pair protons with bulk water protons. The amine-catalyzed exchange is mediated by compounds which are A.T and G.C base sequence specific, intercalators, and outside binders. A mechanism for the selective exchange, involving transient opening and closing of individual A.T base pairs in the duplex, is discussed.

Adenine↗
PubMed2000

Caenorhabditis elegans senses protons through amphid chemosensory neurons: proton signals elicit avoidance behavior.

Acidic pH is known to cause pain sensation through nociceptive neurons as well as taste transduction in mammals. Caenorhabditis elegans avoids an acidic environment (pH lower than approximately 4.0) formed by organic or inorganic acids. This avoidance behavior was dependent on multiple amphid chemosensory neurons, and inhibited by a mutation of capsaicin receptor homologue, and by the addition of amiloride and ruthenium red (inhibitors of proton-gated Na+ channels and capsaicin receptors, respectively). These results indicate that C. elegans recognizes protons as a nociceptive stimulus, through multiple neurons, which elicits avoidance behavior. It is of special interest that a system similar to that of mammalian signal transduction is responsible for this nematode's acid avoidance.

Amiloride↗
PubMed2000

Parity violation in elastic electron-proton scattering and the Proton's strange magnetic form factor

We report a new measurement of the parity-violating asymmetry in elastic electron scattering from the proton at backward scattering angles. This asymmetry is sensitive to the strange magnetic form factor of the proton as well as electroweak axial radiative corrections. The new measurement of A = -4.92+/-0.61+/-0.73 ppm provides a significant constraint on these quantities. The implications for the strange magnetic form factor are discussed in the context of theoretical estimates for the axial corrections.

Journal Article↗
PubMed2002

Measurement of analyzing power for proton-carbon elastic scattering in the coulomb-nuclear interference region with a 22-GeV/c polarized proton beam.

The analyzing power for proton-carbon elastic scattering in the Coulomb-nuclear interference region of momentum transfer, 9.0x10(-3)<-t<4.1x10(-2) (GeV/c)(2), was measured with a 21.7 GeV/c polarized proton beam at the Alternating Gradient Synchrotron of Brookhaven National Laboratory. The ratio of hadronic spin-flip to nonflip amplitude, r(5), was obtained from the analyzing power to be Rer(5)=0.088+/-0.058 and Imr(5)=-0.161+/-0.226.

Journal Article↗
PubMed2004

Evidence for an exotic S= -2, Q= -2 baryon resonance in proton-proton collisions at the CERN SPS.

Results of resonance searches in the Xi(-)pi(-), Xi(-)pi(+), Xi;(+)pi(-), and Xi;(+)pi(+) invariant mass spectra in proton-proton collisions at sqrt[s]=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi(-)pi(-) baryon resonance with mass of 1.862+/-0.002 GeV/c(2) and width below the detector resolution of about 0.018 GeV/c(2). The significance is estimated to be above 4.2sigma. This state is a candidate for the hypothetical exotic Xi(--)(3/2) baryon with S=-2, I=3 / 2, and a quark content of (dsdsū). At the same mass, a peak is observed in the Xi(-)pi(+) spectrum which is a candidate for the Xi(0)(3/2) member of this isospin quartet with a quark content of (dsus[-]d). The corresponding antibaryon spectra also show enhancements at the same invariant mass.

Journal Article↗
PubMed2004

J/psi production from proton-proton collisions at square root of s=200 GeV.

J/psi production has been measured in proton-proton collisions at square root of s=200 GeV over a wide rapidity and transverse momentum range by the PHENIX experiment at the Relativistic Heavy Ion Collider. Distributions of the rapidity and transverse momentum, along with measurements of the mean transverse momentum and total production cross section are presented and compared to available theoretical calculations. The total J/psi cross section is 4.0+/-0.6(stat)+/-0.6(syst)+/-0.4(abs) mu b. The mean transverse momentum is 1.80+/-0.23(stat)+/-0.16(syst) GeV/c.

Journal Article↗
PubMed2004

Novel mechanism of H0 dibaryon production in proton-proton interactions from parton-based Gribov-Regge theory.

A novel mechanism of H0 and strangelet production in hadronic interactions within the Gribov-Regge approach is presented. In this approach the H0 is produced by the same mechanism as usual hadrons, namely, by disintegration of the remnant formed by the exchange of pomerons between the two protons. Rapidity and transverse momentum spectra of the observed hadrons are well described in this approach. In contrast to traditional distillation approaches, here the production of multiple (strange) quark bags does not require large baryon densities or a quark gluon plasma. We calculate the rapidity and transverse momentum distributions as well as the 4pi multiplicity of the H0 for sqrt[s]=17 GeV (Super Proton Synchrotron) and 200 GeV (Relativistic Heavy Ion Collider). In both cases the H0, if it exists, should be observable by the present experiments.

Journal Article↗
PubMed2005

Calculation of proton-deuteron breakup reactions including the Coulomb interaction between the two protons.

The Coulomb interaction between the two protons is fully included in the calculation of proton-deuteron breakup with realistic interactions for the first time. The hadron dynamics is based on the purely nucleonic charge-dependent (CD) Bonn potential and its realistic extension CD Bonn +Delta to a coupled-channel two-baryon potential, allowing for single virtual Delta-isobar excitation. Calculations are done using integral equations in momentum space. The screening and renormalization approach is employed for including the Coulomb interaction. The Coulomb effect on breakup observables is seen at all energies in particular kinematic regimes.

Journal Article↗
PubMed1986

Inhibitors of proton pumping: effect on passive proton transport.

Reported inhibitors of the Characean plasmalemma proton pump were tested for their ability to inhibit the passive H(+) conductance which develops in Chara corallina Klein ex Willd. at high pH. Diethylstilbestrol inhibits the proton pump and the passive H(+) conductance with about the same time course, at concentrations that have no effect on cytoplasmic streaming. N-Ethylmaleimide, a sulfhydryl reagent which is small and relatively nonpolar, also inhibits both pumping and passive conductance of H(+). However, it also inhibits cytoplasmic streaming with about the same time course, and therefore could not be considered a specific ATPase inhibitor. p-Chloromercuribenzene sulfonate (PCMBS), a sulfhydryl reagent which is large and charged and hence less able to penetrate the membrane, does not inhibit pumping or conductance at low concentration. At high concentration, PCMBS sometimes inhibits pumping without affecting H(+) conductance, but since streaming is also inhibited, the effect on the pump cannot be said to be specific. 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide, a water soluble carbodiimide, weakly inhibits both pump and conductance, apparently specifically.

Journal Article↗
PubMed1977

The effective proton conductance of the inner membrane of mitochondria from brown adipose tissue. Dependency on proton electrochemical potential gradient.

The nucleotide-sensitive H+ (OH-) conducting pathway of mitochondria from the brown-adipose tissue of cold-adapted guinea-pigs passes an effective proton current which is directly proportional to the proton electrochemical gradient. At 23 degrees C and pH 7.0 this conductance is 16 nmol H+ - min-1 - mg-1 - mV-1. Addition of 0.2 mM GDP results in a conductance which is linear and low (0.7 nmol H+ - min-1 - mg-1 - mV-1) until deltamicronH+ exceeds 220 mV. At higher values of deltamicronH+, which can be attained by glycerol 3-phosphate oxidation but not palmitoyl-L-carnitine plus malate oxidation, the membrane conductance greatly increases, effectively limiting the maximal deltamicronH+ to 240 mV. High glycerol 3-phosphate concentrations which have the thermodynamic potential to exceed this value of deltamicronH+ instead create a greatly increased rate of controlled respiration. The generality and significance of this device to limit deltamicronH+, and its relation to the nucleotide-sensitive conductance, are discussed.

Acclimatization↗
PubMed1989

Transport of amino acids in Lactobacillus casei by proton-motive-force-dependent and non-proton-motive-force-dependent mechanisms.

Lactobacillus casei 393 cells which were energized with glucose (pH 6.0) took up glutamine, asparagine, glutamate, aspartate, leucine, and phenylalanine. Little or no uptake of several essential amino acids (valine, isoleucine, arginine, cysteine, tyrosine, and tryptophan) was observed. Inhibition studies indicated that there were at least five amino acid carriers, for glutamine, asparagine, glutamate/aspartate, phenylalanine, or branched-chain amino acids. Transport activities had pH optima between 5.5 and 6.0, but all amino acid carriers showed significant activity even at pH 4.0. Leucine and phenylalanine transport decreased markedly when the pH was increased to 7.5. Inhibitors which decreased proton motive force (delta p) nearly eliminated leucine and phenylalanine uptake, and studies with de-energized cells and membrane vesicles showed that an artificial electrical potential (delta psi) of at least -100 mV was needed for rapid uptake. An artificial delta p was unable to drive glutamine, asparagine, or glutamate uptake, and transport of these amino acids was sensitive to a decline in intracellular pH. When intracellular pH was greater than 7.7, glutamine, asparagine, or glutamate was transported rapidly even though the proton motive force had been abolished by inhibitors.

Amino Acids↗
PubMed1991

An analysis of lactose permease "sugar specificity" mutations which also affect the coupling between proton and lactose transport. II. Second site revertants of the thiodigalactoside-dependent proton leak by the Val177/Asn319 permease.

The double mutant of the lactose permease containing Val177/Asn319 exhibits proton leakiness by two pathways (see Brooker, R. J. (1991) J. Biol Chem. 266, 4131-4138). One type of H+ leakiness involves the uncoupled influx of H+ (leak A pathway) while a second type involves the coupled influx of H+ and galactosides in conjunction with uncoupled galactoside efflux (leak B pathway). In the current study, 14 independent lactose permease mutants were isolated from the Val177/Asn319 parent which were resistant to thiodigalactoside growth inhibition but retained the ability to transport maltose. All of these mutants contained a third mutation (besides Val177/Asn319) at one of two sites. Eight of the mutants had Ile303 changed to Phe, while six of the mutants had Tyr236 changed to Asn or His. Each type of triple mutant was characterized with regard to sugar transport, H+ leakiness, and sugar specificity. Like the parental strain, all three types of triple mutant showed moderate rates of downhill lactose transport and were defective in the uphill accumulation of sugars. However, with regard to proton leakiness, the triple mutants fell into two distinct categories. The mutant containing Phe303 was generally less H+ leaky than the parent either via the leak A or leak B pathway. In contrast, the triple mutants containing position 236 substitutions (Asn or His) were actually more H+ leaky via the leak A pathway and exhibited similar H+ leakiness via the leak B pathway at high thiodigalactoside concentrations. The ability of the position 236 mutants to grow better than the parent in the presence of low concentrations of thiodigalactoside appears to be due to a decrease in affinity for this particular sugar rather than a generalized defect in H+ leakiness. Finally, the triple mutants showed a sugar specificity profile which was different from either the Val177/Asn319 parent, the single Val177 mutant, or the wild-type strain. These results are discussed with regard to the effects of mutations on both the sugar and H+ transport pathways.

Base Sequence↗