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PubMed1992

Factors Affecting the Acetylene-Induced Decline during Nitrogenase Assays in Root Nodules of Myrica gale L.

Our goal was to determine why the rate of acetylene reduction by nodules of actinorhizal plants declines after an initial peak value. The decline was eliminated by pretreatment with argon, indicating that the decline is initiated by cessation of ammonia synthesis. When O(2) concentration was decreased during the decline, the rate of acetylene reduction increased. This shows that during the decline there is either O(2) toxicity or competition between respiration and nitrogenase for reductant. The decline was not eliminated when uptake hydrogenase was inactivated by pretreatment with acetylene, showing that cessation of H(2) oxidation is not the primary cause of the decline. The effects of a variety of other treatments on the decline were also studied. Overall, we conclude that the cessation of ammonia formation is the primary cause of the acetylene-induced decline. We hypothesize that the supply of reductant for nitrogenase depends on amino acids that are depleted following cessation of ammonia formation. We also conclude that the initial peak rate of acetylene reduction provides the best measure of nitrogenase activity.

Journal Article↗
PubMed1996

Ultrasound-assisted oxidative cleavage of acetylenic and ethylenic bonds in unsaturated fatty esters with potassium permanganate.

The effect of ultrasound on the oxidation of unsaturated fatty esters was investigated. Unsaturated fatty esters containing acetylenic or olefinic bonds or both were oxidatively cleaved with KMnO4 in aqueous acetic acid (AcOH/H2O, 1:1, vol/vol for olefinic fatty esters and AcOH/H2O, 9:1, vol/vol for acetylenic fatty esters) to yield the corresponding carboxylic acid moieties in quantitative yields, when the reactions were conducted under ultrasound (20 kHz, 53 W/cm2, 8-15 min). The methyl ester derivatives of the carboxylic acid moieties formed were identified by gas-liquid chromatographic analysis. The procedure constitutes a facile method for the determination of the position of the unsaturated center (olefinic or acetylenic) in an unsaturated fatty ester substrate, especially where the unsaturated system consists of an acetylenic bond.

Acetylene↗
PubMed1990

The small-scale production of [U-14C]acetylene from Ba14CO3: application to labeling of ammonia monooxygenase in autotrophic nitrifying bacteria.

A small-scale method has been adapted from an established procedure for the generation of [U-14C]acetylene from inexpensive and commonly available precursors. The method involves the fusing of Ba14CO3 with excess barium metal to produce Ba14C2. The BaC2 is reacted with water to generate acetylene which is then selectively dissolved into dimethyl sulfoxide (DMSO). The results presented demonstrate the effect of Ba:BaCO3 ratio on the concentrations of various gases released during the hydrolysis reaction and quantify the selectivity of the DMSO-trapping process for each gas. [U-14C]Acetylene generated by this method has been used to inactivate ammonia monooxygenase in three species of autotrophic nitrifying bacteria: Nitrosomonas europaea, Nitrosococcus oceanus, and Nitrosolobus multiformis. Our results demonstrate that acetylene inactivation of this enzyme in all three species results in the covalent incorporation of radioactive label into a polypeptide of apparent Mr of 25,000-27,000, as determined by sodium dodecylsulfate-polyacrylamide gel electrophoresis and fluorography.

Acetylene↗
PubMed1989

Effects of acetylene on hydrogenases from the sulfate reducing and methanogenic bacteria.

The effect of acetylene on the activity of the three types of hydrogenase from the anaerobic sulfate reducing bacteria has been investigated. The (Fe) hydrogenase is resistant to inhibition by acetylene while the nickel-containing hydrogenases are inhibited by acetylene with the (NiFe) hydrogenase being 10-50 fold more sensitive than the (NiFeSe) hydrogenase. In addition the Ni(III) EPR signal (g approximately 2.3) of the "as isolated" (NiFe) hydrogenase was significantly decreased in intensity upon exposure to acetylene.

Acetylene↗
PubMed1988

Elimination kinetics of acetylene and Freon 22 in resting and active lungless salamanders.

To quantify diffusion limitation in cutaneous gas exchange, the elimination of two inert gases of different diffusivity, Freon 22 (CHC1F2) and acetylene (C2H2), was measured simultaneously in exclusively skin-breathing lungless salamanders, Desmognathus quadramaculatus. In resting salamanders, elimination of both gases could be described as the sum of three exponential terms. For both the medium and the slow exponential component, the ratio of the respective rate constants (k) for acetylene and Freon averaged 1.77. This value is between the values expected for perfusion limitation (1.00) and diffusion limitation (1.94), indicating combined diffusion and perfusion limitation. In salamanders stimulated to run on a treadmill, the elimination rates and the rate constants increased more for Freon than for acetylene. During spontaneous activity, the increase in elimination of Freon was larger than that of acetylene. These findings suggest an increase in the diffusing capacity of the skin during exercise. Thus the diffusing capacity of salamander skin for gases appears to be variable and to be adjusted to meet the increased O2 requirement during exercise.

Acetylene↗
PubMed1992

Effects of sulfide and low redox potential on the inhibition of nitrous oxide reduction by acetylene in Pseudomonas nautica.

Membrane introduction mass spectrometry was used to investigate the inhibitory effect of acetylene on the nitrous oxide reductase activity of intact cells of Pseudomonas nautica. We studied the effects of the concentrations of nitrate and sulfide, and the redox potential, which have all been implicated in causing a decrease in the inhibitory effects of acetylene during measurements of denitrification in natural environments. There was no evidence that the concentration of nitrate influenced the effect of acetylene. Lowering the redox potential with the reductant Ti(III)-nitrilotriacetate caused a slight alleviation of acetylene inhibition. Much greater effects at the same redox potential were obtained with concentrations of sulfide in the range 1-10 microM.

Acetylene↗
PubMed1997

Antimalarial activity of extracts and fractions from Bidens pilosa and other Bidens species (Asteraceae) correlated with the presence of acetylene and flavonoid compounds.

After interviewing natives and migrants from the Amazon region of Brazil about plants traditionally used for treatment of malaria fever and/or liver disorders, we selected and identified 41 different species, including the native Bidens (Asteraceae). We have undertaken an antimalarial study of Bidens pilosa and other species of Bidens from abroad. The crude ethanol extracts (whole plant, leaves and roots) and the chloroform and butanol fractions from B. pilosa at concentrations of 50 microg/ml caused up to 90% inhibition of Plasmodium falciparum growth in vitro. In vivo the fractions caused partial reduction of Plasmodium berghei parasitemia in mice. The ethanol extracts from nine different Bidens species collected outside Brazil were tested, and seven inhibited parasite growth in vitro by 65-91%. As B. pilosa appears to be a promising antimalarial agent, we further characterized the substances responsible for such activity. HPLC analysis using a photo diode-array detector showed phenyl acetylene and flavonoids in the ethanol extract from the leaves and roots. The chloroform fractions from the roots, which caused 86% inhibition of parasite growth in vitro, contained a major component identified as 1-phenyl-1,3-diyn-5-en-7-ol-acetate. The association of antimalarial activity and the presence of acetylene compounds is discussed. In summary, all species of Bidens which had aliphatic acetylenes (6-14 each) were also very active, whereas extracts of B. parriflora and of B. bitternata with none or the three acetylenes, respectively as reported in literature, were inactive or had a borderline activity in vitro.

Acetylene↗
PubMed2006

Catalytic carbonyl Z-dienylation via multicomponent reductive coupling of acetylene to aldehydes and alpha-ketoesters mediated by hydrogen: Carbonyl insertion into cationic rhodacyclopentadienes.

Exposure of aldehydes or alpha-ketoesters to equal volumes of acetylene and hydrogen gas at ambient temperature and pressure in the presence of cationic rhodium catalysts provides products of carbonyl Z-butadienylation, which arise via multicomponent coupling of four molecules: two molecules of acetylene, a molecule of vicinal dicarbonyl compound, and a molecule of elemental hydrogen. The collective data suggest a catalytic mechanism involving carbonyl insertion into a cationic rhodacyclopentadiene intermediate derived via oxidative dimerization of acetylene. Hydrogenolytic cleavage of the resulting oxarhodacycloheptadiene via formal sigma-bond metathesis provides the product of carbonyl addition and cationic rhodium(I) to close the catalytic cycle. Studies involving the hydrogenation of 1,6-diyne 14a in the presence of alpha-ketoester 6a corroborate the proposed catalytic mechanism. These multicomponent couplings represent the first use of acetylene gas, a basic chemical feedstock, in metal-catalyzed reductive C-C bond formation.

Acetylene↗
PubMed2004

Decarboxylative elimination of enol triflates as a general synthesis of acetylenes.

The enol trifluoromethanesulfonates 4, 8, 12, 17 and 20 of tert-butyl beta-ketodiesters and beta-ketoesters can be hydrolysed to the corresponding carboxylic acids by dissolution in trifluoroacetic acid. The dicarboxylic acids undergo mild decarboxylative elimination to give the acetylenic acids 4 and 9 in aqueous sodium bicarbonate solution at room temperature. Similarly, the monocarboxylic acids give the terminal and mid-chain acetylenes 13, 18, 21, and 24 by refluxing in acetone with potassium carbonate. One of the substituents on the acetylenes can be methyl, primary alkyl, secondary alkyl or ethynyl, and the other can be a carboxylic acid, hydrogen or primary alkyl, but the enol trifluoromethanesulfonates could not be prepared when one of the substituents was tert-butyl, nor when both substituents on the precursor to the acetylene were secondary alkyl.

Acetylation↗
PubMed1998

Reproducibility of the acetylene rebreathe technique for determining cardiac output.

PURPOSE: The acetylene rebreathe technique is a well established method for the determination of cardiac output (Q) at rest and during exercise. We sought to demonstrate that the acetylene rebreathe technique allows for highly reproducible determinations of Q. METHODS: Nine elite male endurance cyclists (VO2max = 68.9 +/- 0.6 mL.kg-1.min-1) performed a modified acetylene rebreathe maneuver during incremental exercise on four repeat test days. A key modification to the method originally described by Grollman was the maintenance of a positive filling pressure during the inhalation portion of the procedure. RESULTS: There were no significant differences in determinations of Q at the same submaximal heart rates on four separate test days. The coefficient of variation for repeat determinations of maximal Q during the same work rate, expressed as the standard deviation of the difference between duplicate measurements, is 4.8%. The coefficient of variation for determinations of maximal Q at the same heart rate on different days, expressed as the standard deviation of the difference between four test days, is 2.6%. CONCLUSION: These findings illustrate that the acetylene rebreathe technique can be used with confidence to assess Q across repeated experimental days.

Acetylene↗
PubMed1981

Selective acetylenic 'suicide' and reversible inhibitors of monoamine oxidase types A and B.

1 A number of aromatic-N-propargyl (acetylenic) compounds and indoleamines were tested for their inhibitory action on monoamine oxidase (MAO) type A and type B using the substrates 5-hydroxytryptamine (5-HT), beta-phenylethylamine (PEA) and dopamine. 2 Structure activity studies with aromatic-N-propragyl (acetylenic) derivatives have shown that MAO inhibitory potency is least dependent on the aromatic portion of the compounds. N-methylated propargyl derivatives are the most active and replacement of the methyl group with a higher alkyl or aromatic group results in significant reduction of activity. The triple bond in the N-propargyl portion is absolutely essential for activity and must be beta-to the nitrogen. It is the acetylenic group that gives these compounds their irreversible MAO inhibitory property. 3 The present study has indicated that since the acetylenic compounds resemble the enzyme substrates the distance between the aromatic ring and the N-propargyl terminal is crucial in designating the type A or type B MAO inhibitory property. For MAO type A inhibition, a distance equivalent to at least three carbon units is required, while for the inhibition of the B type enzyme this distance can be 1 or 2 carbon units. 4 The compounds AGN-1133 and AGN-1135 show most promise in Parkinson's disease or as anti-depressants because of their irreversible selective type B MAO inhibition in vitro and in vivo. 5 A number of indoleamine derivatives were found to be reversible selective type A inhibitors.

Acetylene↗
PubMed1981

Effect of oxygen on acetylene reduction by photosynthetic bacteria.

The effect of dissolved oxygen concentration on nitrogenase activity was studied in three species of photosynthetic bacteria. The O2 concentration in the cell suspension was measured with an O2 electrode inserted into the reaction vessel. Acetylene reduction by whole cells of Rhodopseudomonas capsulata, Rhodospirillum rubrum, and Chromatium vinosum strain D was inhibited 50% by 0.73, 0.32, and 0.26 microM O2, respectively. The inhibition of the activity by O2 in R. capsulata usually was reversed completely by reestablishing anaerobic conditions. In R. rubrum and C. vinosum the inhibition was only partially reversible. The respiration rate of R. capsulata was the highest of the three, that of R. rubrum was intermediate, and that of C. vinosum was lowest. R. capsulata and R. rubrum cells were broken after their acetylene reduction activity in vivo had been completely inhibited by O2, and nitrogenase was found to be active in vitro. A concentration of cyanide that did not affect acetylene reduction activity, but which inhibited 75 to 90% of the O2 uptake by whole cells of R. capsulata, shifted the O2 concentration causing 50% inhibition of nitrogenase activity from 0.73 microM to 2.03 microM. These results are in accordance with the assumption that within a limited range of O2 concentrations, the respiratory activity of the cells is enough to scavenge the O2 and to keep the interior of the cells essentially anaerobic. It is suggested that O2 inhibits nitrogenase activity by competing for a limited supply of electrons. When cyanide is present, respiration is slower but is adequate to keep the nitrogenase environment in the cell anaerobic. The lower respiration rate may allow a greater proportion of the electrons to be used for acetylene reduction.

Acetylene↗
PubMed1977

ATP and acetylene-reducing activity of a sulfate-reducing bacterium.

A sulfate-reducing bacterium, a strain of Desulfovibrio vulgaris, when lactate or pyruvate was supplied as an electron and energy source, reduced acetylene only in the presence of sulfate. Acetylene reduction started after a lag of 1 h. H2 which acts as an electron and energy source for sulfate reduction was unable to reduce acetylene even in the presence of sulfate. It was suggested, from the measurements of the amounts of adenine nucleotides of the bacterium incubated under various conditions, that the bacterium is able to reduce acetylene at a high ATP level or a high ATP/ADP ratio.

Acetylene↗
PubMed1981

Factors affecting vesicle formation and acetylene reduction (nitrogenase activity) in Frankia sp. CpI1.

Vesicle formation and acetylene reduction (nitrogenase activity) were observed when washed hyphae from cultures of Frankia sp. CpI1 were transferred to a nitrogen-free medium containing ethylenediaminetetraacetic acid and succinate. Succinate could be replaced by malate or fumarate, but not other carbon sources. Maximum acetylene reduction and vesicle numbers were observed at a pH of 6.0-6.5, at 25-30 degrees Centigrade, and at atmos pheric Po2 or somewhat less (5-20 kPa). Addition of 1 mM NH4Cl almost completely inhibited vesicle formation and acetylene-reducing activity, but did not immediately inhibit such reducing activity by cultures with preexisting vesicles. Acetylene-reducing activity was never observed in the absence of vesicle formation.

Acetylene↗
PubMed1999

Determination of cardiac output by the Fick method, thermodilution, and acetylene rebreathing in pulmonary hypertension.

Assessment of cardiac output is an important part of the management of patients with pulmonary hypertension. The accuracy of the thermodilution technique in patients with low cardiac output or severe tricuspid regurgitation has been questioned. To address this issue, we simultaneously compared 105 cardiac output measurements by the Fick method and thermodilution in 35 patients with pulmonary hypertension. Moreover, we evaluated the acetylene rebreathing technique, a noninvasive method of determining cardiac output. The mean difference +/- 95% limit of agreement between thermodilution and the Fick method was +0.01 +/- 1.1 L/min. The mean difference +/- 95% limit of agreement between acetylene rebreathing and the Fick method was -0.23 +/- 1.14 L/min. Neither the mean agreement nor the 95% limits of agreement of both thermodilution and acetylene rebreathing with the Fick method were affected by the presence of low cardiac output or severe tricuspid regurgitation. We conclude that thermodilution and acetylene rebreathing are useful tools for assessing cardiac output in patients with pulmonary hypertension, even in the presence of low cardiac output or severe tricuspid regurgitation.

Acetylene↗
PubMed1997

Noninvasive measurement of cardiac output by an acetylene uptake technique and simultaneous comparison with thermodilution in ICU patients.

A simple, accurate, and noninvasive method of cardiac output measurement can be an extremely useful tool for the clinician and researcher. This study used the acetylene gas uptake technique to measure the absorption of acetylene into the pulmonary circulation during a constant exhalation, which is proportional to the pulmonary capillary blood flow and to the cardiac output, assuming no anatomic shunts. We compared cardiac output measured simultaneously by this and by the standard thermodilution (TD) technique in 21 patients in the ICU with a variety of medical and surgical conditions and a wide range of cardiac outputs. We also compared the two techniques in 19 ambulatory patients with a 2-h interval between the invasive and noninvasive test to assess variability over time. The two tests had an excellent correlation when done simultaneously with a correlation coefficient of 0.89 (p < 0.001). With a 2-h interval between the two tests, the correlation coefficient was 0.66 (p = 0.0018). Nine patients in the simultaneous group had cardiomyopathy. When they were excluded, the correlation coefficient increased to 0.96. Most of these patients had documented tricuspid regurgitation (TR), which may underlie the greater difference between acetylene uptake and TD values, with consistently higher TD values in these patients. This study confirms the correlation between the acetylene uptake and the standard invasive TD techniques in sick patients with various medical and surgical conditions and a wide range of cardiac outputs. Furthermore, we believe this would be a more accurate method for measuring cardiac output in patients with cardiomyopathy and TR because it is based only on pulmonary capillary blood flow.

Absorption↗
PubMedDate not supplied

[The gas chromatographic detection of acetylene in cadaveric material].

Acetylene traces were detected by gas chromatography in the cadaveric right crural muscle of a 30-year-old man dead from an explosion of an acetylene reservoir at a plant. Acetylene was identified using the absolute calibration method on 3 standard gas chromatographic columns, reaction gas chromatography, and acetylene "deduction" by silver sulfate on silicagel.

Acetylene↗
PubMedDate not supplied

[Mechanism of the "acetylene effect" during interaction of organophosphorus compounds with cholinesterases].

Here we present data on the anticholinesterase activity of 58 synthesized ethers of phosphorus thioacids with an acetylene bond in the thioether group. Anticholinesterase activity of the compounds, with acetylene group in beta and especially alpha position, in the thioether radical is many times that of their saturated analogs. Reaction between the enzymes and acetylene organophosphorous inhibitors, as well as their saturated analogs, results in phosphorylated enzyme. The triple bond plays a significant role in the acceleration of cholinesterases phosphorylation. Antienzyme activity of acetylene organophosphorous inhibitors is discussed.

Acetylcholinesterase↗