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PubMed2004

Automated measurement and calibration of reactive volatile halogenated organic compounds in the atmosphere.

The automated calibration and analysis of very low mixing ratios of the reactive volatile organic halocarbons CH(3)I, CHCl(3), C(2)H(5)I, 2-C(3)H(7)I, CH(2)Br(2), CH(2)ClI, CHBr(2)Cl, 1-C(3)H(7)I, CH(2)BrI, CHBr(3) and CH(2)I(2) for long term atmospheric field measurements are described. Analytes were pre-concentrated from 3 l of air onto an adsorbent trap cooled to -10 [degree]C using Peltier plates, and rapidly transferred to a gas chromatograph (GC) by resistive heating. A two stage Carboxen 1016/Carbotrap C adsorbent trap allowed good analyte recovery and rapid desorption without the need for post-desorption cryofocussing. Halocarbons were detected using a mass spectrometer (MS) in selective ion mode. Detection limits were between 0.02 and 0.12 pptv (parts per trillion by volume) for approximately hourly samples of CHCl(3), CH(3)I, C(2)H(5)I, 1-C(3)H(7)I, 2-C(3)H(7)I, CH(2)ClI, CH(2)Br(2), CHBr(2)Cl, CH(2)BrI, CHBr(3) and CH(2)I(2) with a precision of 3-8%. A novel calibration system was constructed which utilised fixed volume (50 [micro sign]l) injections of the output of thermostatted permeation tubes into a stream of nitrogen gas in order to dilute parts per million by volume (ppmv) mixing ratios into pptv. The calibration was completely automated, allowing multi-point calibrations during routine operation. The overall accuracy of the measurements is estimated to be +/-15%. The instrument was used continuously for automated atmospheric measurements during a 4-month research cruise from Germany to Antarctica, and a 6 week field campaign at Mace Head, Ireland. The results for CHCl(3) during the latter campaign were within 13% of measurements made by a GC-MS operating continuously at the site within the long term Advanced Global Atmospherics Gases Experiment.

Air Pollutants↗
PubMed1980

Chemical structure and biodegradability of halogenated aromatic compounds. Conversion of chlorinated muconic acids into maleoylacetic acid.

1. An enzyme for the cycloisomerization of 2- and 3-chloro-cis,cis-muconic acid was isolated from 3-chlorobenzoate-grown cells of Pseudomonas sp. B13. It was named muconate cycloisomerase II, because it could it clearly be differentiated by its Km and Vmax. values from an ordinary muconate cycloisomerase, which functioned in benzoate catabolism and exhibited low activity with the chlorinated substrates. 2-Chloro-cis,cis-muconic acid was converted into trans- and 3-chloro-cis,cis--muconic acid into cis-4-carboxymethylenebut-2-en-4-olide together with dehalogenation. 2. An enzyme was isolated from chlorobenzoate-grown cells, which converted the 4-carboxymethylenebut-2-en-4-olides into maleoylacetic acid.

Biodegradation, Environmental↗
PubMed1982

Inhibition of murine leukaemia virus reverse transcriptase by 2-halogenated polyadenylic acids.

Several new analogues of polyadenylic acid [(A)n], i.e. poly(2-fluoroadenylic acid) [(fl2A)n], poly(2-chloroadenylic acid [(cl2A)n], poly(2-bromoadenylic acid) [(br2A)n] and poly(2-iodoadenylic acid) [(io2A)n] have been synthesized and evaluated for their effects on the RNA-directed DNA polymerase (reverse transcriptase) activity of Moloney murine leukaemia virus. All (A)n analogues were found to be potent inhibitors of reverse transcriptase, the order of (decreasing) potency being (fl2A)n greater than (io2A)n greater than (br2A)n greater than (cl2A)n. For all four (A)n analogues the inhibition of reverse transcriptase was competitive with respect to the template-primer. (A)n . oligo(dT). The K1 values were 0.02 microgram/ml for (fl2A)n, 0.1 microgram/ml for (io2A)n, 0.5 microgram/ml for (br2A)n and 8 microgram/ml for (cl2A)n. With a Ki of 0.02 microgram/ml (approx. 0.04 microM), (fl2A)n can be considered as one of the most, if not the most, potent polynucleotide inhibitor of reverse transcriptase that has been described so far.

Halogens↗
PubMed2006

Laboratory-evolved vanadium chloroperoxidase exhibits 100-fold higher halogenating activity at alkaline pH: catalytic effects from first and second coordination sphere mutations.

Directed evolution was performed on vanadium chloroperoxidase from the fungus Curvularia inaequalis to increase its brominating activity at a mildly alkaline pH for industrial and synthetic applications and to further understand its mechanism. After successful expression of the enzyme in Escherichia coli, two rounds of screening and selection, saturation mutagenesis of a "hot spot," and rational recombination, a triple mutant (P395D/L241V/T343A) was obtained that showed a 100-fold increase in activity at pH 8 (k(cat) = 100 s(-1)). The increased K(m) values for Br(-) (3.1 mm) and H(2)O(2) (16 microm) are smaller than those found for vanadium bromoperoxidases that are reasonably active at this pH. In addition the brominating activity at pH 5 was increased by a factor of 6 (k(cat) = 575 s(-1)), and the chlorinating activity at pH 5 was increased by a factor of 2 (k(cat) = 36 s(-1)), yielding the "best" vanadium haloperoxidase known thus far. The mutations are in the first and second coordination sphere of the vanadate cofactor, and the catalytic effects suggest that fine tuning of residues Lys-353 and Phe-397, along with addition of negative charge or removal of positive charge near one of the vanadate oxygens, is very important. Lys-353 and Phe-397 were previously assigned to be essential in peroxide activation and halide binding. Analysis of the catalytic parameters of the mutant vanadium bromoperoxidase from the seaweed Ascophyllum nodosum also adds fuel to the discussion regarding factors governing the halide specificity of vanadium haloperoxidases. This study presents the first example of directed evolution of a vanadium enzyme.

Ascomycota↗