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PubMed1984

Purification and characterization of component A of the methane monooxygenase from Methylococcus capsulatus (Bath).

Methylococcus capsulatus (Bath) possesses a multi-component methane monooxygenase which catalyzes in vivo the conversion of methane to methanol. Component A of this enzyme system, believed to be the oxygenase component, has been purified to near homogeneity (95%). The native protein has a molecular weight of approximately 210,000 and is comprised of three subunits of Mr = 54,000, 42,000, and 17,000, which appear to be present in stoichiometric amounts suggesting an alpha 2, beta 2, gamma 2 arrangement in the native protein. Purified preparations of the protein are virtually colorless and examination of the uv/visible absorption spectrum revealed a peak around 280-290 nm and thereafter a steady decrease in absorbance to longer wavelengths. The ESR spectrum of the oxidized protein gave a signal at g = 4.3, presumably due to rhombic iron, and a radical signal at g = 2.01. Upon reduction with dithionite, a signal at g = 1.934 appeared. Chemical analyses of our purified preparations revealed the presence of iron (2.3 mol/mol) and zinc (0.2-0.5 mol/mol): molybdenum, copper, nickel, heme, and acid-labile sulfur were all virtually absent. On ultra thin layer isoelectric focusing, purified component A was judged to have a pI between 5.0 and 5.1. Extracts prepared from a variety of other methanotrophs failed to show any cross-reaction to antibody raised against M. capsulatus component A.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

[Electron transport chain in a thermophilic methane-oxidizing culture of Methylococcus thermophilus].

The electron transport chain was studied in the obligate methane oxidizing culture of Methylococcus thermophilus during the oxidation of methanol (the source of carbon) which is an oxidized derivative of methane as well as during the oxidation of hydroxylamine which is an intermediate in the oxidation of ammonium (the source of nitrogen) by Mc. thermophilus cells. Cytochromes a, b and c are involved in electron transport. Cytochrome cco and cytochrome c554 have been isolated from the cell-free extract of Mc. thermophilus and purified. A scheme for electron transport operating in the oxidation of methanol and hydroxylamine is suggested on the basis of studying the characteristics of these cytochromes. Cytochrome a was shown to be a component of terminal oxidase. Cytochromes b are connected with membranes and also found in the composition of hydroxylamine oxidase. Cytochrome cco and, possibly, terminal oxidase (cytochromes a) are involved, in the oxidation of CH3OH by methanol dehydrogenase, in electron transport; cytochrome c554 as well as cytochrome b and c in the composition of hydroxylamine oxidase participate in electron transport in the oxidation of NH2OH by hydroxylamine oxidase. The characteristics of the electron transport system in Mc. thermophilus are discussed.

Alcohol Oxidoreductases↗
PubMed1982

[Stability of acetate buffered methanal solutions].

The determination of the concentration in acetate puffered methanol solutions (formaldehyde solutions) with pH = 5.60 during 14 months disproved the opinion of the limited durability of these solutions. Neither a significant decrease of the methanal mass concentration nor a noticeable change of the pH value could be proved during the period of the examination under different influences of light and temperature. Methanal solutions can be applied farther in the practice of the preservation.

Acetates↗
PubMed1993

Bis(5-amidino-2-benzimidazolyl)methane and related amidines are potent, reversible inhibitors of mast cell tryptases.

Tryptase is the major secretory protease of human mast cells and is proposed to be involved in neuropeptide processing and tissue inflammation. Exploration of the biology of tryptase has been hindered by the lack of potent, selective inhibitors. The current study explores the properties of aromatic diamidines as inhibitors of dog and human tryptase. The strongest inhibitors of tryptase in this series are bis(5-amidino-2-benzimidazolyl)methane (BABIM) and (5-amidino-2-benzimidazolyl)-(5-(N,N'-dimethylamidino)-2- benzimidazolyl)methane, which exhibit K(i) values of 1.8 and 1.4 nM, respectively, in blocking the hydrolysis of tosyl-L-Gly-Pro-Lys-4-nitroanilide by human tryptase. These compounds are approximately 10,000-fold more potent than benzamidine, and are the strongest reversible inhibitors of tryptase described to date. Other aromatic mono- and diamidines, including amiloride and pentamidine, are less potent. Nonetheless, they abolish tryptase activity at high inhibitor concentrations. The rank order of tryptase inhibitor potency parallels that of inhibitors tested against trypsin. BABIM, the only highly active member of this series whose potency against other targets has been examined previously, is a far stronger inhibitor of tryptase than of other trypsin-like serine proteases, including those involved with hemostasis, fibrinolysis and the complement system. Therefore, BABIM appears to have selective affinity for tryptase. In addition to inhibiting tryptase-induced hydrolysis of peptide-based chromogenic substrates, BABIM blocks completely the reversal of vasoactive intestinal peptide-induced relaxation of isolated trachea by dog tryptase. Thus, BABIM and related amidines are potent inhibitors of mast cell tryptases that may be useful in exploring mast cell protease biology.

Amiloride↗
PubMed1995

Geometry of the soluble methane monooxygenase catalytic diiron center in two oxidation states.

BACKGROUND: The hydroxylase component of soluble methane monooxygenase (sMMO) contains a dinuclear iron center responsible for the oxidation of methane to methanol. As isolated, the center is in the oxidized, diiron(III) state. The 2.2 A resolution X-ray structure of the oxidized hydroxylase, Hox, from Methylococcus capsulatus (Bath) was previously determined at 4 degrees C. In this structure the two iron atoms are bridged by a glutamate, a hydroxide ion, and an acetate ion, and additionally coordinated to two His residues, three Glu residues, and a water molecule. RESULTS: The 1.7 A resolution crystal structures of the sMMO hydroxylase from Methylococcus capsulatus (Bath) in both its oxidized diiron(III), Hox, and dithionite-treated, reduced diiron(II), Hred, oxidation states were determined at -160 degrees C. The structure of the diiron center in Hox differs from that previously reported at 2.2 A resolution and 4 degrees C. Although the hydroxide bridge is retained, the bidentate, bridging ligand assigned as acetate is replaced by a weakly coordinating monoatomic water bridge. In the resulting four-membered Fe(OH)Fe(OH2) ring, the Fe ... Fe distance is shortened from 3.4 A to 3.1 A. In protomer A of Hred, the hydroxide bridge is displaced by an oxygen atom of Glu243, which undergoes a carboxylate shift from its terminal monodentate binding mode in Hox to a mode in which the carboxylate is both monoatomic bridging and bidentate chelating. We therefore conclude that the center has been reduced to the diiron(II) oxidation state. Both iron atoms are coordinated to five ligands and weakly to a sixth water molecule in the resulting structure. The diiron center in protomer B of Hred has the same composition as those in Hox. In both the oxidized and reduced structures, the diiron core is connected through hydrogen bonds involving exogenous species to Thr213 in the active site cavity. CONCLUSIONS: The diiron center in Hox can change its exogenous ligand coordination and geometry, a property that could be important in the catalytic cycle of sMMO. In Hred, a carboxylate shift occurs, extruding hydroxide ion and opening coordination sites for reaction with O2 to form the diiron(III) peroxo intermediate, Hperoxo. Residue Thr213 may function in catalysis.

Binding Sites↗
PubMed1995

Geometry of the soluble methane monooxygenase catalytic diiron center in two oxidation states.

BACKGROUND: The hydroxylase component of soluble methane monooxygenase (sMMO) contains a dinuclear iron center responsible for the oxidation of methane to methanol. As isolated, the center is in the oxidized, diiron(III) state. The 2.2 A resolution X-ray structure of the oxidized hydroxylase, Hox, from Methylococcus capsulatus (Bath) was previously determined at 4 degrees C. In this structure the two iron atoms are bridged by a glutamate, a hydroxide ion, and an acetate ion, and additionally coordinated to two His residues, three Glu residues, and a water molecule. RESULTS: The 1.7 A resolution crystal structures of the sMMO hydroxylase from Methylococcus capsulatus (Bath) in both its oxidized diiron(III), Hox, and dithionite-treated, reduced diiron(II), Hred, oxidation states were determined at -160 degrees C. The structure of the diiron center in Hox differs from that previously reported at 2.2 A resolution and 4 degrees C. Although the hydroxide bridge is retained, the bidentate, bridging ligand assigned as acetate is replaced by a weakly coordinating monoatomic water bridge. In the resulting four-membered Fe(OH)Fe(OH2) ring, the Fe ... Fe distance is shortened from 3.4 A to 3.1 A. In protomer A of Hred, the hydroxide bridge is displaced by an oxygen atom of Glu243, which undergoes a carboxylate shift from its terminal monodentate binding mode in Hox to a mode in which the carboxylate is both monoatomic bridging and bidentate chelating. We therefore conclude that the center has been reduced to the diiron(II) oxidation state. Both iron atoms are coordinated to five ligands and weakly to a sixth water molecule in the resulting structure. The diiron center in protomer B of Hred has the same composition as those in Hox. In both the oxidized and reduced structures, the diiron core is connected through hydrogen bonds involving exogenous species to Thr213 in the active site cavity. CONCLUSIONS: The diiron center in Hox can change its exogenous ligand coordination and geometry, a property that could be important in the catalytic cycle of sMMO. In Hred, a carboxylate shift occurs, extruding hydroxide ion and opening coordination sites for reaction with O2 to form the diiron(III) peroxo intermediate, Hperoxo. Residue Thr213 may function in catalysis.

Binding Sites↗
PubMed2025

MmoD and MmoG Are Crucial for the Synthesis of Soluble Methane Monooxygenase in Methanotrophs.

Soluble methane monooxygenase (sMMO) from methanotrophs has been extensively investigated for decades. However, major knowledge gaps persist regarding the synthesis mechanism of sMMO, particularly concerning the ambiguous roles of mmoD and mmoG in the sMMO gene cluster. Here, the functions of mmoD and mmoG were investigated in a model methanotrophic strain, Methylotuvimicrobium buryatense 5GB1C. Both genes were found to be essential for the functional expression of sMMO. Genetic and biochemical data supported the hypothesis that MmoG acts as a folding chaperone for both MmoX and MmoR, while MmoD serves as an assembly chaperone for the hydroxylase component. The functional expression of sMMO in Escherichia coli was achieved in an mmoD- and mmoG-dependent manner. In addition, deletion of mmoD dramatically reduced the transcription of the sMMO cluster in M. buryatense 5GB1C, implying that MmoD may regulate the sMMO cluster via an unknown mechanism. Knockout of neither mmoD nor mmoG abolished the essential feature of "copper switch", indicating that they do not serve as the initial regulators of "copper switch". These results demonstrate the crucial roles of mmoD and mmoG in sMMO synthesis and offer new insights into heterologous expression of sMMO.

Oxygenases↗
PubMed1997

Development of genetic approaches for the methane-producing archaebacterium Methanococcus maripaludis.

Methanococcus maripaludis is a strict anaerobe that utilizes H2 or formate as an electron donor for CO2 reduction to methane. Recent progress in development of genetic systems in this archaebacterium makes it an excellent model system for molecular and biochemical studies. This progress includes development of methods for growth on solid medium, enriching auxotrophic mutants, efficient transformation, and random insertional inactivation of genes. Genetic markers for both puromycin and neomycin resistance are available. Lastly, a shuttle vector has been constructed from a cryptic methanococcal plasmid. These technical advances made it possible to utilize genetic approaches for the study of autotrophic CO2 assimilation in methanococci.

Acetic Acid↗
PubMed2007

A logistic model for the prediction of the influence of water on the solid waste methanization in landfills.

This article deals with the impact of water content of solid waste on biogas production kinetics in landfills. This impact has been proved in the laboratory thanks to anaerobic biodegradation experiments on paper/cardboard waste samples. A strong dependence with the moisture level was observed for both kinetic rates and maximum methane production. In this article, a logistic model is proposed to simulate the biogas production rate. It is chosen as simple as possible in order to allow for a correct identification of the model parameters given the experimental data available. The moisture dependency is introduced through a linear weighing of the biomass specific growth rate and of the amount of accessible organic substrate. It is directly linked to physical properties of the waste: the holding capacity and the minimal moisture level allowing the presence of free water.

Bacteria, Anaerobic↗
PubMed1978

Simultaneous determination of hydromorphone, hydrocodone and their 6alpha- and 6beta-hydroxy metabolites in urine using selected ion recording with methane chemical ionization.

A selected ion recording using chemical ionization (methane) is described for the simultaneous measurement of hydrocodone, hydromorphone and their respective 6alpha- and 6beta-hydroxymetabolites in human urine. The samples were acid-hydrolyzed, extracted and derivatized by silylation. Only partial resolution of the components on 3% OV-17 was achieved but was sufficient for their determination. The [M+1]+ ions of the drugs and metabolites as well as the [M+29]+ ion of the internal standard were recorded. The assay was sensitive down to c. 0.01 microgram ml-1. The relative standard deviation of standards processed along with the samples ranged from 4.5-8.2%. Hydrocodone was found to be metabolized in man primarily by O-demethylation and 6-keto reduction. Hydromorphone was excreted mainly in the unchanged form (after acid-hydrolysis) with only minor amounts of the 6-hydroxymetabolites being detected. A lack of stereoselectivity in the metabolic reduction ofhydrocodone was observed.

Codeine↗
PubMed1979

Methane-oxygen enhanced negative ion mass spectra of polychlorinated diphenyl ethers.

Methane-oxygen enhanced negative ion mass spectra of 15 chlorinated diphenyl ethers contained some combination of [M-]-., [M-1]-, [M-19]-, [M-36]-, [M-55]-, and [M+35]- anions. The relative abundances of these ions are related to the chlorine substitution pattern. Similar ions appear in the negative ion spectra of polychlorinated anisoles. The study of known isomers of polychlorinated model compounds extends the utility of the negative ion method in the analysis of polychlorinated aromatics such as polychlorinated biphenyls, dioxins and furans. The spectra were shown to be very dependent on the temperature of the ion source; a temperature change of 25 degrees C was shown to have pronounced effects. Spectral variation with temperature has implications for computer library searches, ultimate sensitivity limits and analysis in the presence of interfering isobaric ions.

Chlorobenzenes↗
PubMed1984

Positive and electron capture negative ion methane chemical ionization mass spectrometry of pyrrolizidine alkaloids.

Pulsed positive and negative ion methane chemical ionization mass spectrometry of pyrrolizidine alkaloids is reported. Positive ion spectra are characterized by a high relative abundance of [MH]+ ions while the negative ion spectra exhibit ion peaks due to dissociative electron capture. Fragmentation in both positive and negative ion spectra primarily occurs at the ester groups with the positive charge residing with the pyrrolizidine ring system while the negative charge in contrast tends to reside with the necic acid moiety. Esterification at C-9 v. C-7 can be distinguished for non-cyclic esters of retronecine in the positive ion spectra.

Chemical Phenomena↗
PubMed2006

Transition-metal-catalyzed sequential cross-coupling of bis(iodozincio)methane and -ethane with two different organic halides.

Bis(iodozincio)methane, prepared from diiodomethane and zinc, reacts with an organic halide in the presence of a transition-metal catalyst to give an iodozinciomethylenated compound; this then reacts with another organic halide to form a C--C bond. The overall process connects two electrophiles with one carbon atom. Bis(iodozincio)ethane can also undergo this transformation, yielding a new stereogenic center. The asymmetric induction of this stereogenic center was investigated by using a chiral palladium catalyst.

Catalysis↗
PubMed1988

Ultrathin coating of plasma polymer of methane applied on the surface of silicone contact lenses.

Silicone rubber has great advantages as a contact lens material because of its very high oxygen permeability, softness, and excellent mechanical strength and durability. Practical application is hampered by inherent characteristics of elastomers, i.e., high tackiness and highly hydrophobic surface properties. By applying a thin layer, e.g., 5 nm, of plasma polymer of methane, it was found that all these disadvantages can be eliminated without sacrificing high oxygen permeation rate, e.g., less than 15% reduction. Optimization of operational parameters to achieve this task has been investigated. It was also found that under optimum conditions the coating withstood severe and repeated flexing of the contact lens.

Contact Lenses↗
PubMed2006

High-precision, automated stable isotope analysis of atmospheric methane and carbon dioxide using continuous-flow isotope-ratio mass spectrometry.

Small-scale developments have been made to an off-the-shelf continuous-flow gas chromatography/isotope-ratio mass spectrometry (CF-GC/IRMS) system to allow high-precision isotopic analysis of methane (CH(4)) and carbon dioxide (CO(2)) at ambient concentrations. The repeatability (1sigma) obtainable with this system is 0.05 per thousand for delta(13)C of CH(4), 0.03 per thousand for delta(13)C of CO(2), and 0.05 per thousand for delta(18)O of CO(2) for ten consecutive analyses of a standard tank. An automated inlet system, which allows diurnal studies of CO(2) and CH(4) isotopes, is also described. The improved precision for CH(4) analysis was achieved with the use of a palladium powder on quartz wool catalyst in the combustion furnace, which increased the efficiency of oxidation of CH(4) to CO(2). The automated inlet further improved the precision for both CH(4) and CO(2) analysis by keeping the routine constant. The method described provides a fast turn-around in samples, with accurate, reproducible results, and would allow a long-term continuous record of CH(4) or CO(2) isotopes at a site to be made, providing information about changing sources of the gases both seasonally and interannually.

Air Pollution↗
PubMed2006

Development of two-dimensional gas chromatography/isotope ratio mass spectrometry for the stable carbon isotopic analysis of C(2)-C(5) non-methane hydrocarbons emitted from biomass burning.

A two-dimensional gas chromatography/combustion/isotope ratio mass spectrometry (2D-GC/C/IRMS) system was developed for stable carbon isotopic measurements of C(2)-C(5) non-methane hydrocarbons (NMHCs) in biomass burning smoke. The 2D-GC/C/IRMS system successfully improved the accuracy and precision for the measurements of C(4) and C(5) saturated compounds in a smoke sample by selective injection of target compounds into a combustion furnace and consequently allowed us to provide complete baseline separation for all individual NMHCs. The analytical precision of the delta(13)C of each compound was better than 0.5 per thousand for more than 500 pmolC injections and 2.1 per thousand for 30 pmolC injections, which was estimated from replicate analysis of standard gases. This system was applied to the analysis of NMHCs in smoke samples collected from laboratory biomass burning experiments. From the combustion of three fuel materials (rice straw, pine wood, and maize), we found that the isotopic fractionation between fuel material and individual NMHCs is almost independent of the fuel material and thus the delta(13)C values of the fuel materials are reflected in delta(13)C values of most of NMHCs. However, only i-butane emitted from maize combustion showed anomalous (13)C-depletion of -11.6 per thousand relative to the delta(13)C value of maize. Such a large (13)C depletion suggests the specific isotopic fractionation process which is attributed to the maize combustion itself or the chemical properties of i-butane during production from a radical recombination reaction.

Biomass↗
PubMed2000

Influence of heavy metals on methane oxidation in tropical rice soils.

In a laboratory incubation study, the effect of select heavy metals on methane (CH4) oxidation in two rice soils was investigated under two moisture regimes. Heavy metals differed in their effect on CH4 oxidation in both soils under the two water regimes. Cr significantly inhibited CH4 oxidation in the alluvial soil at 60% moisture holding capacity, while Cu stimulated the process. On the contrary, Zn inhibited CH4 oxidation in both alluvial and laterite soils only under flooded conditions. Application of rice straw alleviated the inhibitory effect of heavy metals on CH4 oxidation and CO2 production. Inhibition of CH4 oxidation in the alluvial soil was related to the methanotrophic bacterial population in Cr- and Zn-amended alluvial soil.

Metals, Heavy↗