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31.
Sub-Parts-Per-Billion Nitrate Method: Use of an N2O-Producing Denitrifier to Convert NO3− or 15NO3− to N2O 下载免费PDF全文
A more sensitive analytical method for NO3− was developed based on the conversion of NO3− to N2O by a denitrifier that could not reduce N2O further. The improved detectability resulted from the high sensitivity of the 63Ni electron capture gas chromatographic detector for N2O and the purification of the nitrogen afforded by the transformation of the N to a gaseous product with a low atmospheric background. The selected denitrifier quantitatively converted NO3− to N2O within 10 min. The optimum measurement range was from 0.5 to 50 ppb (50 μg/liter) of NO3− N, and the detection limit was 0.2 ppb of N. The values measured by the denitrifier method compared well with those measured by the high-pressure liquid chromatographic UV method above 2 ppb of N, which is the detection limit of the latter method. It should be possible to analyze all types of samples for nitrate, except those with inhibiting substances, by this method. To illustrate the use of the denitrifier method, NO3− concentrations of <2 ppb of NO3− N were measured in distilled and deionized purified water samples and in anaerobic lake water samples, but were not detected at the surface of the sediment. The denitrifier method was also used to measure the atom% of 15N in NO3−. This method avoids the incomplete reduction and contamination of the NO3− -N by the NH4+ and N2 pools which can occur by the conventional method of 15NO3− analysis. N2O-producing denitrifier strains were also used to measure the apparent Km values for NO3− use by these organisms. Analysis of N2O production by use of a progress curve yielded Km values of 1.7 and 1.8 μM NO3− for the two denitrifier strains studied. 相似文献
32.
Niels Peter Revsbech Lars Peter Nielsen Peter Bondo Christensen Jan Srensen 《Applied microbiology》1988,54(9):2245-2249
The construction of a microsensor which can be used to measure O2 and N2O simultaneously is described. The microsensor exhibited a linear response to both O2 and N2O, and the response to N2O was independent of the O2 concentration and vice versa. The N2O detection limit of a microsensor with a tip diameter of 20 μm was around 1 μmol liter−1. The signals for O2 and N2O were affected by hydrogen sulfide, but other interfering agents were not observed in the biofilms and sediments analyzed. Microprofiles of O2 and N2O were measured in a biofilm which was exposed to acetylene to block the N2O reductase activity of denitrifying bacteria. O2 penetrated about 0.5 mm into the biofilm and was not affected by acetylene, but the N2O concentration at 1.4 mm depth increased from 32 to 411 μmol liter−1 after the addition of the inhibitor. The shape of the N2O profile after the addition of acetylene showed that denitrification (denitrifying activity) was detectable in all anoxic layers of the biofilm. 相似文献
33.
L M Baddour D L Smalley M M Hill G D Christensen 《Canadian journal of microbiology》1988,34(7):901-905
Proposed virulence factors, including multiple antibiotic resistance and slime-mediated adherence, among coagulase-negative staphylococci colonizing healthy individuals from two different study populations were examined. Resistance to methicillin was more commonly seen than initially anticipated. In addition, adherence characteristics, as quantitated by a microtiter plate method, were very similar to those of strains of coagulase-negative staphylococci causing nosocomial infections. 相似文献
34.
Shawn Doonan Filippo Martini Sebastiana Angelaccio Stefano Pascarella Donatella Barra Francesco Bossa 《Journal of molecular evolution》1986,23(4):328-335
Summary We report here the complete amino acid sequences of the cytosolic and mitochondrial aspartate aminotransferases from horse heart. The two sequences can be aligned so that 48.1% of the amino acid residues are identical. The sequences have been compared with those of the cytosolic isoenzymes from pig and chicken, the mitochondrial isoenzymes from pig, chicken, rat, and human, and the enzyme fromEscherichia coli. The results suggest that the mammalian cytosolic and mitochondrial isoenzymes have evolved at equal and constant rates whereas the isoenzymes from chicken may have evolved somewhat more slowly. Based on the rate of evolution of the mammalian isoenzymes, the geneduplication event that gave rise to cytosolic and mitochondrial aspartate aminotransferases is estimated to have occurred at least 109 years ago. The cytosolic and mitochondrial isoenzymes are equally related to the enzyme fromE. coli; the prokaryotic and eukaryotic enzymes diverged from one another at least 1.3×109 years ago. 相似文献
35.
P Cornelissen M Cornelissen G Van der Perre A B Christensen F Ammitzb?ll C Dyrbye 《Journal of biomechanics》1986,19(7):551-561
The influence of soft tissues and joints on the vibration of the human tibia was examined by modal analysis on amputated lower limbs, where the soft tissues and the fibula were dissected gradually. Measurements were made in two different set ups, IFR and BRA, which were both designed to monitor fracture healing. In IFR, vibrations are generated by hammer impact on a relaxed hanging lower leg, with the knee flexed. Resonant frequencies are determined by a computer Fourier transform procedure. In BRA, a steady state vibration is induced in a lower leg, supported near the ankle and the tibial tuberosity, using an electromagnetic shaker. Resonant frequencies are determined from the maxima in vibration amplitudes. In both set ups the soft tissues have a similar influence on the vibration of the tibia: the skin hardly influences the determined modal parameter. The mass of the muscles influences both the resonant frequency and the damping. The fibula has a stiffening effect on the tibia. The influence of the joints is small in the IFR-set up: the tibia vibrates in conditions close to those for the free-free vibration. In the BRA-set up, the supports determine the boundary conditions. 相似文献
36.
Sedimentation studies of DNA from chromosomes extracted from human mitotic cells showed that highmolecular-weight DNA can be obtained if cell hypotonic treatments and prolonged metaphase blocks are avoided. Two types of large double-stranded DNA were observed. One of these (M
r
= 2.5×108) appeared as a size class with characteristics reminiscent of the chromosomal DNA subunit hypothesis. However, this DNA is the decay product of larger molecules, whose minimum molecular weight is 6×108. 相似文献
37.
The discovery of a trans-stimulation property associated with lysine exodus from lysosomes of human fibroblasts has enabled us to characterize a system mediating the transport of cationic amino acids across the lysosomal membrane of human fibroblasts. The cationic amino acids arginine, lysine, ornithine, diaminobutyrate, histidine, 2-aminoethylcysteine, and the mixed disulfide of cysteine and cysteamine all caused trans-stimulation of the exodus of radiolabeled lysine from the lysosomal fraction of human fibroblasts at pH 6.5. In contrast, neutral and acidic amino acids did not affect the rate of lysine exodus. trans-Stimulation of lysine exodus was observed over the pH range from 5.5 to 7.6, was specific for the L-isomer of the cationic amino acid, and was intolerant to methylation of the alpha-amino group of the amino acid. The lysosomotropic amine, chloroquine, greatly retarded lysine exodus, whereas the presence of sodium ion was without effect. The specificity and lack of Na+ dependence of this lysosomal transport system is similar to that of System y+ present on the plasma membrane of human fibroblasts. In addition, we find cystine exodus from the lysosomal fraction of cystinotic human fibroblasts to be greatly retarded as compared to that of normal human fibroblasts with half-times of exodus similar to those reported for the lysosomes of cystinotic and normal human leukocytes (Gahl, W. A., Tietze, F., Bashan, N., Steinherz, R., and Schulman, J. D. (1982) J. Biol. Chem. 257, 9570-9575). In contrast, normal and cystinotic human fibroblasts did not show any differences with regard to lysine efflux or its trans-stimulation by cationic amino acids. An important mechanism by which cysteamine treatment of cystinosis allows cystine escape from lysosomes may be the ability of the mixed disulfide of cysteine and cysteamine formed by sulfhydryl-disulfide exchange to migrate by this newly discovered system mediating cationic amino acid transport. 相似文献
38.
The melanization response of Aedes trivittatus and the black-eyed Liverpool (LVP) and Rocke-feller (RKF) strains of Aedes aegypti against intrathoracically inoculated Brugia pahangi microfilariae (mff) that previously had penetrated LVP, RKF, or A. trivittatus midguts in vitro was assessed at 1, 3, and 5 days postinoculation (PI). LVP and RKF midgut-derived mff almost totally avoided the melanization response and developed normally in LVP strain A. aegypti, and although over 90% of these mff died by 5 days PI in RKF mosquitoes, the majority of these were not melanized. A. aegypti midgut-derived mff also were able to avoid the response of A. trivittatus in 33–43% of the cases. Penetration through A. trivittatus midguts, however, did not significantly affect the ability of mff to avoid the melanization response in any of the mosquitoes examined. Allogeneic and xenogeneic tissue inplants were accepted by all three mosquito species examined. Data presented support the hypothesis that mff avoid immune recognition in compatible mosquitoes by coating themselves with midgut material(s) during penetration of the midgut in their migration to the hemocoel. 相似文献
39.
Roshan B. Christensen J. R. Christensen Ian Koenig Christopher W. Lawrence 《Molecular & general genetics : MGG》1985,201(1):30-34
Summary Using a nonselective method, we have estimated the proportion of untargeted mutations in the lacI gene of E. coli by transferring either irradiated or unirradiated F pro lac plasmids from an excision deficient donor to an excision deficient pro lac deleted recipient that had been irradiated and allowed to induce recA dependent functions for 30 min. We find that about 10 percent of the mutations induced by either 3.5 Jm-2 or 7 Jm-2 UV are untargeted. 相似文献
40.
Christopher W. Lawrence Beth R. Krauss Roshan B. Christensen 《Mutation research》1985,150(1-2):211-216
Previously isolated mutations in baker's yeast, Saccharomyces cerevisiae, that impair induced mutagenesis were all identified with the aid of tests that either exclusively or predominantly detect base-pair substitutions. To avoid this bias, we have screened 11 366 potentially mutant clones for UV-induced reversion of the frameshift allele, his4–38, and have identified 10 mutants that give much reduced yields of revertants. Complementation and recombination tests show that 6 of these carry mutations at the previously known REV1, REV1 and REV3 loci, while the remaining 4 define 3 new genes, REV4 (2 mutations), REV5 and REV6. The rev4 mutations are readily suppressed in many genetic backgrounds and, like the rev5 mutation, impart only a limited deficiency for induced mutagenesis: it is likely, therefore that the REV4+ and REV5+ gene functions are only remotely concerned with this process. The rev6 mutants have a more general deficiency, however, as well as marked sensitivity to UV and an increased spontaneous mutation rate, properties that suggest the REV6 gene is directly involved in mutation induction. The REV5 gene is located about 1 cM proximal to CYC1 on chromosome X. 相似文献