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PubMed1999

Measurement of hydroxyl radical-generated methane sulfinic acid by high-performance liquid chromatography and electrochemical detection.

A liquid chromatographic (HPLC) method has been developed for direct quantitative determination of methane sulfinic acid (MSA) produced by hydroxyl radical oxidation of dimethyl sulfoxide. This method measures MSA directly by HPLC separation and electrochemical oxidation following rapid extraction from intact cells. MSA can be measured in tissue extracts at 0.04 nmol (equivalent to 2 microM). Using this technique, MSA production in paraquat-treated bean leaves is demonstrated. When compared with the widely used dye-binding technique, this method simplifies the preparation of the extract by eliminating two steps required in the dye-binding method: removal of interfering lipophilic compounds and the derivitization (color reaction) of the MSA.

Chromatography, High Pressure Liquid↗
PubMed1993

19F NMR study of the interaction of fluoride ion with ribonucleotide reductase and methane monooxygenase.

The relaxation rates of fluoride, determined by 19F NMR spectroscopy, were greatly increased in the presence of protein Mn-A, the manganese form of the hydroxylase component of methane monooxygenase. This demonstrates that F- interacts with the manganese center of protein Mn-A. On the contrary, protein Mn-R2, the manganese form of the small subunit of ribonucleotide reductase, had no effect on the relaxation rate of F-. This reflects differences between the two proteins in terms of the accessibility of the metal ion sites, despite the strong similarities of these sites.

Binding Sites↗
PubMed1998

Preparation, Characterization, and Catalytic Properties of Clay-Based Nickel Catalysts for Methane Reforming.

Naturally occurring clays and pillared clays are used as supports of nickel catalysts for the methane reforming reaction with carbon dioxide to synthesis gas. The structural and textural characteristics of the supports and catalysts are systematically examined by N2 adsorption/desorption and X-ray diffraction (XRD) techniques. It is found that the pore structures and surface properties of supports greatly affect the catalytic activities of the catalysts prepared. The catalysts supported on the mesoporous clays or pillared clays are obviously superior to those on microporous supports because the mesoporous supports are highly thermal stable compared to the microporous ones. It is found that introducing lanthanum to the supports can improve the catalyst basicity and thus enhance the catalytic activities of these catalysts. Deactivation of catalysts prepared and factors influencing their stability are also discussed. Copyright 1998 Academic Press.

Journal Article↗
PubMed1994

Preliminary crystallographic analysis of methane mono-oxygenase hydroxylase from Methylosinus trichosporium OB3b.

The hydroxylase component of the enzyme methane mono-oxygenase from Methylosinus trichosporium OB3b has been crystallized in the orthorhombic space group C222(1) with unit cell dimensions a = 264.5 A, b = 71.2 A, c = 139.4 A. The crystals grow as square, thick plates and diffract to beyond 2 A resolution. There is one half of the hydroxylase dimer in the asymmetric unit.

Crystallization↗
PubMed1996

The Hot Bands of Methane between 5 and 10 μm

Experimental line intensities of 1727 transitions arising from nine hot bands in the pentad-dyad system of methane are fitted to first and second order using the effective dipole moment expansion in the polyad scheme. The observed bands are nu3 - nu2, nu3 - nu4, nu1 - nu2, nu1 - nu4, 2nu4 - nu4, nu2 + nu4 - nu2, nu2 + nu4 - nu4, 2nu2 - nu2, and 2nu2 - nu4, and the intensities are obtained from long-path spectra recorded with the Fourier transform spectrometer located at Kitt Peak National Observatory. For the second order model, some of the 27 intensity parameters are not linearly independent, and so two methods (extrapolation and effective parameters) are proposed to model the intensities of the hot bands. In order to obtain stable values for three of these parameters, 1206 dyad (nu4, nu2) intensities are refitted simultaneously with the hot band lines. The simultaneous fits to first and second order lead to rms values respectively of 21.5% and 5.0% for the 1727 hot band lines and 6.5% and 3.0% for the 1206 dyad lines. The band intensities of all 10 pentad-dyad hot bands are predicted in units of cm-2 atm-1 at 296 K to range from 0.931 (for 2nu4 - nu4) to 7.67 x 10(-5) (for 2nu4 - nu2). The total intensities are also estimated to first order for two other hot band systems (octad-pentad and tetradecad-octad) that give rise to weak transitions between 5 and 10 μm.

Journal Article↗
PubMed1996

The High-Resolution Fourier Transform Spectrum of Dideuterated Methane CH2D2 in the Region between 1900 and 2400 cm-1

The infrared spectrum of doubly deuterated methane CH2D2 has been recorded in the region from 1900 to 2400 cm-1 at almost Doppler-limited resolution by using two high-resolution Fourier transform spectrometers. The vibrational bands observed include 2nu4, nu4 + nu7, 2nu7, nu2, nu8, nu4 + nu9, and nu7 + nu9, which were analyzed by taking into account Coriolis and Fermi interactions among them and also those with nu4 + nu5, nu3 + nu7, and nu5 + nu7. Most of the centrifugal distortion constants were constrained to appropriate values, while the vibrational term value and three rotational constants in each of the seven excited states were adjusted along with Coriolis and Fermi interaction parameters by the least-squares analysis of the observed spectrum. The vibration-rotation interaction constants alphas thus determined for the nu2 and nu8 states were combined with those of other fundamental states already published to calculate the equilibrium C-H distance.

Journal Article↗
PubMed1998

Simultaneous Determination of Force Constants and Dipole Moment Derivatives of Methane.

The expressions of the effective Hamiltonian and dipole moment spectroscopic parameters in the tetrahedral formalism are used simultaneously to fit the force field and dipole moment derivatives of the methane molecule. Data, the so-called "observed parameters," are the values of the spectroscopic parameters determined from the frequencies and line strengths analyses. The ambiguities of most parameters (in the polyad scheme) are treated consistently with the Hamiltonian reduction chosen in the frequency analyses. As an illustration, the method is applied to the tetrahedral XY4 isotopic species only. The quadratic and cubic force field constants have been determined in addition to the linear and six of the seven quadratic dipole moment derivatives. The observed parameters are reproduced with a standard deviation of 4%. The results are compared with previous works and it is moreover shown that the introduction of the dipole moment data removes some correlations between the force constants. Copyright 1998 Academic Press.

Journal Article↗
PubMed2000

The Intensities of Methane in the 3-5 µm Region Revisited.

The analysis of the linestrengths of the infrared spectrum of methane (12 and 13) in the 3-5 µm region has been revisited on the basis of new measurements from Fourier transform spectra recorded at Kitt Peak under various optical densities. A simultaneous fit of these new data with previously reported tunable difference-frequency laser data has been done. An effective transition moment model in tensorial form up to the third order of approximation within the Pentad scheme has been used. The standard deviations achieved are very close to the experimental precision: 3 and 1.5%, respectively, for the two sets of data for the (12)CH(4) molecule, representing a substantial improvement with respect to earlier studies. The integrated bandstrengths obtained in the present work differ from previously reported values by factors ranging from -5 to +6%. The correction for the nu(3) band, the strongest band of the Pentad system, is +2% with respect to the study of Hilico et al. [J. C. Hilico, J. P. Champion, S. Toumi, V. G. Tyuterev, and S. A. Tashkun, J. Mol. Spectrosc. 168, 455-476 (1994)]. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Vibrational Excitations of Methane in the Framework of a Local-Mode Anharmonic Model.

The stretching and bending vibrations of methane are described in a local-mode anharmonic symmetry adapted model. Both Hecht- and Fermi-like interactions are considered. We start by establishing the Hamiltonian of the system in terms of internal coordinates and momenta. The Hamiltonian is then rewritten in terms of local creation (annihilation) operators a(dagger)(i)(a(i)), which are later anharmonized by means of the deformation of the harmonic oscillator algebra to the U(2) algebra. This procedure corresponds to the exact Morse result for the dominant matrix elements involved in the harmonically coupled anharmonic oscillator model (HCAO) introduced by Child and Lawton. We have carried out a fit to 40 experimental levels with an rms deviation of 1.17 cm(-1). In addition, we present a description of the dipole transition intensities. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

The Continuum of Water Vapor Mixed with Methane: Absolute Absorption at 239 GHz and Linewidth Calculations.

In the aim of achieving a better understanding of the molecular mechanisms involved in the absorption continuum of the water-vapor rotational spectrum, various H(2)O-X mixtures are investigated in an atmospheric window in the mmw range. In the present study, the X mixing gas is methane. Absolute absorption rates have been measured at 239 GHz. The dependence on pressure as well as temperature has been obtained. The experimental data are compared with models using conventional line profiles. As these models require the knowledge of the collisional half-widths of H(2)O broadened by CH(4), theoretical calculations using the complex Robert-Bonamy formalism have been carried out. A "continuum effect" is observed when comparing the experimental absorption with the models, as well as for the magnitude of the absorption discrepancy and for the strong temperature dependence of this absorption. The effect is compared for various X mixing gases to the collisional broadening efficiency in the impact approximation. Copyright 2000 Academic Press.

Journal Article↗
PubMed1993

Effect of novel compound, 1-methyl-1-piperidino methane sulfonate (MPMS), on the osmoprotectant activity of glycine betaine, choline and L-proline in Escherichia coli.

A novel compound, 1-methyl-1-piperidino methane sulfonate (MPMS), was found to block the osmoprotectant activity of choline and L-proline, but not glycine betaine in Escherichia coli. MPMS was more active against salt-sensitive than salt-resistant strains, but had no effect on the salt tolerance of a mutant which was unable to transport choline, glycine betaine and proline. Growth of E. coli in NaCl was inhibited by MPMS and restored by glycine betaine, but not by choline or L-proline. Uptake of radiolabeled glycine betaine, choline or L-proline by cells grown at high osmolarity was not inhibited when MPMS and the radioactive substrates were added simultaneously. Preincubation for 5 min with MPMS reduced the uptake of choline and L-proline, but not glycine betaine. Similar incubation with MPMS had no effect on the uptake of radiolabeled glucose or succinate. The toxicity of MPMS was much lower than that of the L-proline analogues L-azetidine-2-carboxylic acid and 3,4-dehydro-DL-proline. The exact mechanism by which MPMS exerts its effect is not entirely clear. MPMS or a metabolite may interfere with the activity of several independent permeases involved in the uptake of osmoprotective compounds, or the conversion of choline to glycine betaine, or effect the expression of some of the osmoregulatory genes.

Azetidinecarboxylic Acid↗
PubMed1983

Repair of methyl methane sulfonate-damaged phage by Haemophilus influenzae.

Seven mutants of Haemophilus influenzae strain Rd (mmsA-) have been isolated that are more sensitive to methyl methane sulfonate (mms) than recombination-deficient (recA-) mutants. The mutations cotransformed about 25% with the strA locus while the five studied clustered tightly; they are all probably allelic. The mutants are not sensitive to ultraviolet radiation, X-rays, or nitrous acid. Mms-damaged phage HP1 plated very inefficiently on these mutants, indicating that they lack the first step in the excision repair of the lesion N3-methyladenine (m3A). Incubation of damaged phage at 30 degrees C in the absence of mms resulted in a steady decline of viability when the phage were plated on the wild mmsA+ host but an initial steep rise was seen when it was plated on an mmsA- mutant. The rise is explained by the assumption that m3A lesions hydrolyzed off the DNA giving rise to repairable apurinic sites by both the mmsA+ and mmsA- hosts. No decline in viability was observed when hydroxylamine was present in the medium. This compound is known to prevent or slow down beta-elimination. The delayed decline in viability is therefore explained by assuming that apurinic sites give rise to beta-elimination-induced single strand breaks in the phage DNA that cannot be repaired by either host. Marker rescue experiments indicated that these breaks did not interrupt injection of phage DNA.

Bacteriophages↗
PubMed1978

DNA repair processes in germ cells demonstrated in ejaculated sperms of rabbits treated with methyl methane sulfonate.

Male rabbits were treated with a single i.v. injection of 22.5 mg/kg methyl methane sulfonate (MMS). 0--24 h later [3H]-thymidine was injected in both testicles. Incorporation of the isotope in germ cell DNA was demonstrated in ejaculated sperms. In controls labeled sperms were demonstrated first on day 40--43. These cells were in the preleptotene spermatocyte phase at the time of [3H]-thmidine injection. In rabbits treated with MMS significant radioactivity occurred in sperms collected from day 19 onwards. These cells were in late spermatocyte and early spermatid phase of maturation when [3H]-thymidine was injected. Incorporation of thymidine in these cell populations is interpreted as an expression of unscheduled DNA synthesis, a repair process initiated after chemical damage of germ cell DNA by MMS. The usefulness of the rabbit test system within the framework of conventional mutagenicity screening tests is discussed.

Animals↗
PubMed1981

Methyl methane-sulphonate (MMS) induced SCEs are reduced by the BrdU used to visualise them.

SCE induction in synchronised CHO cells treated with methyl methane sulphonate (MMS) in G1 was studied over successive pairs of cell cycles by introducing bromodeoxyuridine (BrdU) at consecutive G1 stages. When individual cell cycle SCE values were calculated from the data, anomalous results were obtained with ratios of 1.0 : 1.8 : 2.1 for the first three cycles but a negative value for the fourth cycle. Further studies using different BrdU concentrations showed that MMS induced SCEs were reduced by values exceeding 50% in DNA containing high levels of incorporated BrdU. This reduction was dose dependent and accounted for the anomalous results obtained over successive cycles. Lesions leading to chromatid exchanges were also reduced by the same mechanism. SCEs induced by UV irradiation were also decreased but those induced by the cross-linking agent nitrogen mustard (HN2) remained unaffected. The results indicate that not only are SCE lesions induced by MMS, UV or HN2 expressed independently of the "spontaneous" SCEs induced by BrdU but that SCE lesions are multiple in nature. Mechanisms by which SCE lesions could be repaired in BrdU containing DNA are discussed. SCE lesions in MMS treated cells arrested in G1 with arginine deprived medium (ADM) are repaired without the presence of BrdU in the DNA. An opposite effect is seen however in the control cells, where SCEs are increased with time spent in ADM arrest. These interactions between the effects of MMS, BrdU and ADM arrest are discussed.

Animals↗
PubMed1989

Ethyl methane sulfonate- and bleomycin-generated deletion mutations at HPRT locus in xeroderma pigmentosum complementation group D fibroblasts.

Immortalized fibroblasts from a male patient with xeroderma pigmentosum from complementation group D (XP-D) were treated with either ethyl methane sulfonate (EMS) or bleomycin (BLM) to obtain mutations in hypoxanthine phosphoribosyltransferase (HPRT) activity. The aneuploid parental cell line, MH3-XPD, was found to have a single copy of the HPRT gene, indicating that this cell line remained physically hemizygous for this locus during the transformation process. Subcloning of 6-thioguanine-resistant (6TG') isolates resulted in clones without detectable HPRT activity. Continued maintenance in elevated concentrations of 6TG (30-60 muM) produced cell populations with negligible growth in counterselection medium. No HPRT-deficient clones arose from unmutagenized cell cultures. Molecular analysis of the HPRT mutations in five clones with undetectable HPRT activity showed that four had large deletions. Two bleomycin-generated isolates were both found to have an approximately 28-kb intragenic deletion beginning with the first intron near exon 1 and ending within the fourth intron near exon 4. Messenger RNA from these clones was truncated by approximately 370 nucleotides. Our findings indicate that these two clones originated from the same mutational event within a founder cell. The three EMS-induced mutants fell into two classes: a putative point mutation or small deletion and two complete gene deletions.

Bleomycin↗
PubMed1984

Timing of mutation-fixation events in ethyl methane sulfonate-treated Chinese hamster cells.

Exposure of single Chinese hamster ovary (CHO) cells to the mutagen, ethyl methane sulfonate, produces two types of mutant colonies lacking glucose-6-phosphate dehydrogenase activity: colonies uniformly deficient in enzyme activity, and mosaic colonies containing both mutant and nonmutant cell phenotypes in various relative proportions and sectored patterns (1/8, 1/4, 1/2). We find that the relative size of the mutant sector in these mosaic colonies primarily reflects the cell division at which the mutation was genetically fixed. Thus, the mutation-fixation event occurs before the first cell division in 1/2 sector and pure mutant colonies, between the first and second divisions for 1/4 sectors, and between the second and third divisions for 1/8 sectors. Delay in the formation of mutations could also explain the phenomenon of "mutation expression time" which is observed when drug resistance is used to select for mutants. Colony sectoring offers for the first time in mammalian cells the opportunity to observe an agent's effect on the timing of the mutational process.

Animals↗
PubMed1990

Pathomorphological changes in rat brain choroid plexus due to administration of the amine-curing agent, bis(4-amino-3-methylcyclohexyl)methane.

Repeated oral administration of an amine-curing agent for epoxy resin, bis(4-amino-3-methylcyclohexyl)methane, gave rise to severe damage in the choroid plexus of rat brain. The damaged epithelium presented varying degrees of swelling and hydropic vacuolation on light microscopy, and varying numbers of vacuoles and inclusion bodies, frequently with lamellar structure, on transmission electron microscopy. Scanning electron microscopy of the choroid plexus disclosed some irregularity in the size of epithelial cells and occasional loss of microvilli. These changes in the choroid plexus were closely correlated with the dosage of the agent administered and the period of administration. In spite of the severe changes in the choroid plexus, no neurological abnormalities were observed in the animals during the experimental period.

Animals↗