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1.
José G. Dórea Wade Wimer Rejane C. Marques Christopher Shade 《Biological trace element research》2011,140(3):262-271
A simplified thiourea-based chromatography method, originally developed for methyl and inorganic mercury, was adapted to separate
methylmercury (MeHg), ethylmercury (EtHg), and inorganic mercury (HgII) in infants' hair. Samples were weighed and leached with an acidic thiourea solution. Leachates were concentrated on a polymeric
resin prior to analysis by Hg-thiourea liquid chromatography/cold vapor atomic fluorescence spectrometry. All but one sample
showed small amounts of EtHg, and four of the six analyzed samples had proportionally higher HgII as a percent of total Hg. Breastfed infants from riverine Amazonian communities are exposed to mercury in breast milk (from
high levels of maternal sources that include both fish consumption and dental amalgam) and to EtHg in vaccines (from thimerosal).
The method proved sensitive enough to detect and quantify acute EtHg exposure after shots of thimerosal-containing vaccines.
Based on work with MeHg and HgII, estimated detection limits for this method are 0.050, 0.10, and 0.10 ng g−1 for MeHg, HgII, and EtHg, respectively, for a 20-mg sample. Specific limits depend on the amount of sample extracted and the amount of extract
injected. 相似文献
2.
Behavior of mercury in the Patuxent River estuary 总被引:12,自引:0,他引:12
An overview of a comprehensive study of the behavior and fate of mercury in the estuarine Patuxent River is presented. Total Hg (HgT) and methylmercury (MeHg) exhibited weakly non-conservative behavior in the estuary. Total Hg concentrations ranged from 6 ng L-1 in the upper reaches of the sub-urbanized tidal freshwater river to <0.5 ng L-1 in the mesohaline lower estuary. Filterable (0.2 µm) HgT ranged from 0.2 to 1.5 ng L-1. On average, MeHg accounted for <5% of unfiltered HgT and <2% of filterable HgT. Dissolved gaseous section Hg (DGHg) concentrations were highest (up to 150 pg L-1) in the summer in the mesohaline, but were not well correlated with primary production or chlorophyll a, demonstrating the complex nature of Hg0 formation and cycling in an estuarine environment. Organic matter content appeared to control the HgT content of sediments, while MeHg in sediments was positively correlated with HgT and organic matter, and negatively correlated with sulfide. MeHg in sediments was low (0.1 to 0.5% of HgT). Preliminary findings suggest that net MeHg production within sediments exceeds net accumulation. Although HgT in pore waters increased with increasing sulfide, bulk MeHg concentrations decreased. The concentration of MeHg in sediments was not related to the concentration of HgT in pore waters. These observations support the hypothesis that sulfide affects the speciation and therefore bioavailability of dissolved and/or solid-phase Hg for methylation. Comparison with other ecosystems, and the negative correlation between pore water sulfide and sediment MeHg, suggest that sulfide limits production and accumulation of MeHg in this system. 相似文献
3.
Mercury Analysis of Acid- and Alkaline-Reduced Biological Samples: Identification of meta-Cinnabar as the Major Biotransformed Compound in Algae
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The biotransformation of HgII in pH-controlled and aerated algal cultures was investigated. Previous researchers have observed losses in Hg detection in vitro with the addition of cysteine under acid reduction conditions in the presence of SnCl2. They proposed that this was the effect of Hg-thiol complexing. The present study found that cysteine-Hg, protein and nonprotein thiol chelates, and nucleoside chelates of Hg were all fully detectable under acid reduction conditions without previous digestion. Furthermore, organic (R-Hg) mercury compounds could not be detected under either the acid or alkaline reduction conditions, and only β-HgS was detected under alkaline and not under acid SnCl2 reduction conditions. The blue-green alga Limnothrix planctonica biotransformed the bulk of HgII applied as HgCl2 into a form with the analytical properties of β-HgS. Similar results were obtained for the eukaryotic alga Selenastrum minutum. No evidence for the synthesis of organomercurials such as CH3Hg+ was obtained from analysis of either airstream or biomass samples under the aerobic conditions of the study. An analytical procedure that involved both acid and alkaline reduction was developed. It provides the first selective method for the determination of β-HgS in biological samples. Under aerobic conditions, HgII is biotransformed mainly into β-HgS (meta-cinnabar), and this occurs in both prokaryotic and eukaryotic algae. This has important implications with respect to identification of mercury species and cycling in aquatic habitats. 相似文献
4.
Daniel Cossa Cédric Garnier Roselyne Buscail Francoise Elbaz-Poulichet Nevenka Mikac Nathalie Patel-Sorrentino Erwan Tessier Sylvain Rigaud Véronique Lenoble Charles Gobeil 《Biogeochemistry》2014,119(1-3):35-43
Methylation of mercury (Hg) is the crucial process that controls Hg biomagnification along the aquatic food chains. Aquatic sediments are of particular interest because they constitute an essential reservoir where inorganic divalent Hg (HgII) is methylated. Methylmercury (MeHg) concentrations in sediments mainly result from the balance between methylation and demethylation reactions, two opposite natural processes primarily mediated by aquatic microorganisms. Thus, Hg availability and the activity of methylating microbial communities control the MeHg abundance in sediments. Consistently, some studies have reported a significant positive correlation between MeHg and HgII or total Hg (HgT), taken as a proxy for HgII, in aquatic sediments using enzyme-catalyzed methylation/demethylation mechanisms. By compiling 1,442 published and unpublished HgT–MeHg couples from lacustrine, riverine, estuarine and marine sediments covering various environmental conditions, from deep pristine abyssal to heavily contaminated riverine sediments, we show that a Michaelis–Menten type relationship is an appropriate model to relate the two parameters: MeHg = aHgT/(K m + HgT), with a = 0.277 ± 0.011 and K m = 188 ± 15 (R 2 = 0.70, p < 0.001). From K m variations, which depend on the various encountered environmental conditions, it appears that MeHg formation and accumulation are favoured in marine sediments compared to freshwater ones, and under oxic/suboxic conditions compared to anoxic ones, with redox potential and organic matter lability being the governing factors. 相似文献
5.
Aspects of Bioavailability of Mercury for Methylation in Pure Cultures of Desulfobulbus propionicus (1pr3)
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We have previously hypothesized that sulfide inhibits Hg methylation by decreasing its bioavailability to sulfate-reducing bacteria (SRB), the important methylators of Hg in natural sediments. With a view to designing a bioassay to test this hypothesis, we investigated a number of aspects of Hg methylation by the SRB Desulfobulbus propionicus, including (i) the relationship between cell density and methylmercury (MeHg) production, (ii) the time course of Hg methylation relative to growth stage, (iii) changes in the bioavailability of an added inorganic Hg (HgI) spike over time, and (iv) the dependence of methylation on the concentration of dissolved HgI present in the culture. We then tested the effect of sulfide on MeHg production by this microorganism. These experiments demonstrated that under conditions of equal bioavailability, per-cell MeHg production was constant through log-phase culture growth. However, the methylation rate of a new Hg spike dramatically decreased after the first 5 h. This result was seen whether methylation rate was expressed as a fraction of the total added Hg or the filtered HgI concentration, which suggests that Hg bioavailability decreased through both changes in Hg complexation and formation of solid phases. At low sulfide concentration, MeHg production was linearly related to the concentration of filtered HgI. The methylation of filtered HgI decreased about fourfold as sulfide concentration was increased from 10−6 to 10−3 M. This decline is consistent with a decrease in the bioavailability of HgI, possibly due to a decline in the dissolved neutral complex, HgS0. 相似文献
6.
Plant and soil microbial community responses to solid waste leachates diffusion on grassland 总被引:2,自引:0,他引:2
Litterfall from trees has been identified as an important pathway for deposition of mercury (Hg) and methylmercury (MeHg) in forested catchments, but very little is known about the role of ground vegetation in deposition and cycling of Hg compounds. This study was conducted to identify the origin of Hg compounds in the ground vegetation, and to estimate the role of its litterfall with respect to pools and fluxes of Hg in a coniferous forest in the German Fichtelgebirge mountains. Above and below ground biomass of the dominant ground vegetation (Vaccinium myrtillus, Deschampsia flexuosa and Calamagrostis villosa) were sampled at several plots successively during the growing season. The fluxes to the soil via litterfall of the ground vegetation were calculated using contents of Hg and MeHg in the annual fractions of aboveground biomass. With fluxes of 0.4 – 7.8 mg Hgtotal ha–1 a–1 and 0.01 – 0.04 mg MeHg ha–1 a–1 (depending on the plant species) this pathway contributes only a few percent to the total deposition of both compounds in the catchment. To identify the uptake pathways of Hg compounds, the same plant species were grown in a pot experiment with addition of isotope labelled Hg compounds (202Hg2+, Me198Hg) to a clean sand substrate. Only small proportions of 202Hg and Me198Hg in the substrate were taken up by the plants, but in all cases the proportion translocated into aboveground biomass after uptake was greater in case of Me198Hg. Thus, internal recycling in the plant-soil system is a source especially for MeHg in the ground vegetation. However, as compared to the input of Hg compounds by tree litterfall and storage in the forest floor, Hgtotal and MeHg in ground vegetation are of minor importance. High volatilization of added Hg isotopes raises the question of a re-emission of Hg compounds by the transpiration flux of the ground vegetation. 相似文献
7.
Hiroshi Yamaguchi Jakub ?ebera Jiro Kondo Shuji Oda Tomoyuki Komuro Takuya Kawamura Takenori Dairaku Yoshinori Kondo Itaru Okamoto Akira Ono Jaroslav V. Burda Chojiro Kojima Vladimír Sychrovsky Yoshiyuki Tanaka 《Nucleic acids research》2014,42(6):4094-4099
We have determined the three-dimensional (3D) structure of DNA duplex that includes tandem HgII-mediated T–T base pairs (thymine–HgII–thymine, T–HgII–T) with NMR spectroscopy in solution. This is the first 3D structure of metallo-DNA (covalently metallated DNA) composed exclusively of ‘NATURAL’ bases. The T–HgII–T base pairs whose chemical structure was determined with the 15N NMR spectroscopy were well accommodated in a B-form double helix, mimicking normal Watson–Crick base pairs. The Hg atoms aligned along DNA helical axis were shielded from the bulk water. The complete dehydration of Hg atoms inside DNA explained the positive reaction entropy (ΔS) for the T–HgII–T base pair formation. The positive ΔS value arises owing to the HgII dehydration, which was approved with the 3D structure. The 3D structure explained extraordinary affinity of thymine towards HgII and revealed arrangement of T–HgII–T base pairs in metallo-DNA. 相似文献
8.
Methane emissions from rice paddies natural wetlands,lakes in China: synthesis new estimate 总被引:2,自引:0,他引:2
Huai Chen Qiu'an Zhu Changhui Peng Ning Wu Yanfen Wang Xiuqin Fang Hong Jiang Wenhua Xiang Jie Chang Xiangwen Deng Guirui Yu 《Global Change Biology》2013,19(1):19-32
Sources of methane (CH4) become highly variable for countries undergoing a heightened period of development due to both human activity and climate change. An urgent need therefore exists to budget key sources of CH4, such as wetlands (rice paddies and natural wetlands) and lakes (including reservoirs and ponds), which are sensitive to these changes. For this study, references in relation to CH4 emissions from rice paddies, natural wetlands, and lakes in China were first reviewed and then reestimated based on the review itself. Total emissions from the three CH4 sources were 11.25 Tg CH4 yr?1 (ranging from 7.98 to 15.16 Tg CH4 yr?1). Among the emissions, 8.11 Tg CH4 yr?1 (ranging from 5.20 to 11.36 Tg CH4 yr?1) derived from rice paddies, 2.69 Tg CH4 yr?1 (ranging from 2.46 to 3.20 Tg CH4 yr?1) from natural wetlands, and 0.46 Tg CH4 yr?1 (ranging from 0.33 to 0.59 Tg CH4 yr?1) from lakes (including reservoirs and ponds). Plentiful water and warm conditions, as well as its large rice paddy area make rice paddies in southeastern China the greatest overall source of CH4, accounting for approximately 55% of total paddy emissions. Natural wetland estimates were slightly higher than the other estimates owing to the higher CH4 emissions recorded within Qinghai‐Tibetan Plateau peatlands. Total CH4 emissions from lakes were estimated for the first time by this study, with three quarters from the littoral zone and one quarter from lake surfaces. Rice paddies, natural wetlands, and lakes are not constant sources of CH4, but decreasing ones influenced by anthropogenic activity and climate change. A new progress‐based model used in conjunction with more observations through model‐data fusion approach could help obtain better estimates and insights with regard to CH4 emissions deriving from wetlands and lakes in China. 相似文献
9.
Bacterially mediated ionic mercury reduction to volatile Hg0 was shown to play an important role in the geochemical cycling of mercury in a contaminated freshwater pond. This process, and the degradation of methylmercury, could be stimulated to reduce the concentration of methylmercury that is available for accumulation by biota. A study testing the utility of this approach is described.Abbreviations HgR
inorganic mercury resistance
- Org-Hg
organomercury
- Org-HgR
organomercury resistance
- SRB
sulfate reducing bacteria
- Methyl-B12
methylcobalamine 相似文献
10.
Mercury inputs and outputs at a small lake in northern Minnesota 总被引:1,自引:0,他引:1
Storages and cycling of total mercury (HgT), methylmercury (MeHg), and Hg0 are described for Spring Lake, a small bog lake in the Marcell Experimental Forest in north-central Minnesota. We quantified
photoredox transformations, MeHg photolysis, burial to the sediments, and internal and external loadings of HgT and MeHg. Atmospheric deposition was the main input of HgT; MeHg was supplied by a combination of atmospheric, near-shore wetland, and biotic (methylation) sources. HgT outputs were dominated by burial (67%), and Hg0 evasion accounted for 26% of HgT outputs. The watershed of Spring Lake is small (3.7× lake surface area), and accordingly, bog and upland runoff were minor
contributors to both HgT and MeHg inputs. Wet deposition was ∼9% of total MeHg input, and other external inputs (runoff, sediment porewater) provided
only an additional 7%, indicating that internal production of MeHg was occurring in the lake. Photolysis of MeHg, measured
in the field and laboratory, removed ∼3× the lake mass of MeHg (20 mg) annually, and was the dominant sink for MeHg. Residence
times of MeHg and HgT in the lake were 48 and 61 days, respectively, during the open-water season, compared with only 8 days for the residence
time of MeHg on settling particles (seston). Photoreduction of Hg2+ to Hg0 was greater than the reverse reaction (Hg0 photooxidation), and the residence time of Hg0 in the photic zone was short (hours). Data from this study show active cycling of all the measured species of mercury (HgT, MeHg, and Hg0) and the importance of MeHg photolysis and photo-redox processes. 相似文献
11.
Sina Berger Inyoung Jang Juyoung Seo Hojeong Kang Gerhard Gebauer 《Biogeochemistry》2013,115(1-3):317-332
Rice is staple food of half of mankind and paddy soils account for the largest anthropogenic wetlands on earth. Ample of research is being done to find cultivation methods under which the integrative greenhouse effect caused by emitted CH4 and N2O would be mitigated. Whereas most of the research focuses on quantifying such emissions, there is a lack of studies on the biogeochemistry of paddy soils. In order to deepen our mechanistic understanding of N2O and CH4 fluxes in rice paddies, we also determined NO3 ? and N2O concentrations as well as N2O isotope abundances and presence of O2 along soil profiles of paddies which underwent three different water managements during the rice growing season(s) in (2010 and) 2011 in Korea. Largest amounts of N2O (2 mmol m?2) and CH4 (14.5 mol m?2) degassed from the continuously flooded paddy, while paddies with less flooding showed 30–60 % less CH4 emissions and very low to negative N2O balances. In accordance, the global warming potential (GWP) was lowest for the Intermittent Irrigation paddy and highest for the Traditional Irrigation paddy. The N2O emissions could the best be explained (*P < 0.05) with the δ15N values and N2O concentrations in 40–50 cm soil depth, implying that major N2O production/consumption occurs there. No significant effect of NO3 ? on N2O production has been found. Our study gives insight into the soil of a rice paddy and reveals areas along the soil profile where N2O is being produced. Thereby it contributes to our understanding of subsoil processes of paddy soils. 相似文献
12.
Susan Winch Danielle Fortin David R. S. Lean Michael Parsons 《Geomicrobiology journal》2013,30(2):112-129
Large quantities of Hg remain in tailings dumps from historical Nova Scotian gold mines. Depth profiles of total Hg (HgT) and methylmercury (MeHg) were compared with geochemical and microbiological variables, to identify factors influencing MeHg levels in tailings. HgT and MeHg were highly variable in tailings (0.2–73.5 μ mol kg? 1 and < dl-56.4 nmol kg? 1, respectively), and were influenced by a complex set of in situ factors. Elevated MeHg was linked with > 5 μ mol kg?1 HgT, organic matter, hydrology, abundance and activity of sulfate reducing bacteria, and demethylation processes. Methylmercury levels in tailings from a wet, bog-like site appeared to undergo seasonal fluctuations, with higher concentrations measured in September and October, and lower concentrations in May. Evaluations of amalgamation tailings should examine MeHg and HgT transport out of low-lying, saturated tailings dumps after snowmelt and major rainfall events, and should take into account the possibility of seasonal variation in MeHg levels in northern regions. 相似文献
13.
Background and aims
Rice grains contaminated by mercury (Hg) and methylmercury (MeHg) pose risks to human health. This study evaluated the relative importance of genotype, environment and genotype-environment interactions on the accumulation of total Hg (THg) and MeHg in brown rice.Methods
A pot trial with four rice genotypes and 10 Hg-contaminated paddy soils was conducted under greenhouse conditions. The effects of genotype, environment and genotype-environment interactions on brown rice THg and MeHg accumulation were assessed by an Additive Main Effects and Multiplicative Interaction (AMMI) model.Results
THg and MeHg concentrations in brown rice ranged from 20.5 to 75.5 μg kg?1 and 2.24 to 54.7 μg kg?1, respectively. The AMMI model indicated that genotype explained 41.1 and 19.6%, environment described 40.6 and 55.8%, and the genotype-environment interaction explained 11.9 and 20.0% of the variation in brown rice THg and MeHg levels, respectively. Brown rice THg positively correlated with water-soluble Hg and total potassium, but negatively correlated with total sulphur, iron, total organic carbon and nickel in soils. Brown rice MeHg negatively correlated with soil pH and selenium.Conclusion
THg accumulation in brown rice was mainly affected by both genotype and environment, whereas MeHg accumulation was largely determined by environment.14.
稻田秸秆还田:土壤固碳与甲烷增排 总被引:38,自引:0,他引:38
基于我国农田土壤有机质长期定位试验和稻田甲烷排放试验成果,将全国稻田划分为单季区和双季区.根据土壤有机质试验数据,分析了秸秆还田在我国两个稻田区的单季稻田、水旱轮作稻田和双季稻田的固碳潜力.同时根据我国稻田甲烷排放试验数据,采用取平均排放系数的方法,估算了我国稻田在无秸秆还田情况下的甲烷排放总量;结合IPCC推荐的方法和参数,估算了我国稻田秸秆还田后甲烷排放总量及增排甲烷的全球增温潜势.结果表明:在中国稻田推广秸秆还田的固碳潜力为10.48TgC.a-1,对减缓全球变暖的贡献为38.43TgCO2-eqv.a-1;但秸秆还田后稻田甲烷排放将从无秸秆还田的5.796Tg.a-1增加到9.114Tg.a-1;秸秆还田引起甲烷增排3.318Tg.a-1,其全球增温潜势达82.95TgCO2-eqv.a-1,为土壤固碳减排潜力的2.158倍.可见,推广秸秆还田后,中国稻田增排甲烷的温室效应会大幅抵消土壤固碳的减排效益,是一项重要的温室气体泄漏. 相似文献
15.
Eukaryotic algae were studied to determine their ability to biotransform HgII under aerated and pH controlled conditions. All algae converted HgII into β-HgS and Hg0 to varying degrees. When HgII was administered as HgCl2 to the algae, biotransformation by species of Chlorophyceae (Selenastrum
minutum and Chlorella fusca var. fusca) was initiated with β-HgS synthesis (K
1/2 of hours) and concomitant Hg° evolution occurred in the first hour. Hg° synthesis was impeded by the formation of β-HgS and
this inhibition was released in C. fusca var. fusca when cellular thiols were oxidized by the addition of dimethylfumarate (DMF). The diatom, Navicula pelliculosa (Bacillariophyceae), converted a substantially greater proportion of the applied HgII into Hg0, whereas the thermophilic alga, Galdieria sulphuraria (Cyanidiophyceae), rapidly biotransformed as much as 90% of applied HgII into β-HgS (K
1/2 ≈ 20 min). This thermophile was also able to generate Hg0 even after all exogenously applied HgCl2 had been biotransformed. The results suggest that β-HgS may be the major dietary mercurial for grazers of contaminated eukaryotic
algae. 相似文献
16.
17.
Chenchao Xu Naifang Zhang Kaihang Zhang Shuyao Li Qing Xia Jing Xiao Maojun Liang Weilei Lei Junpan He Gaiping Chen Chengjun Ge Xunhua Zheng Jianguo Zhu Shuijin Hu Roger T. Koide Mary K. Firestone Lei Cheng 《Global Change Biology》2023,29(16):4670-4685
Continued current emissions of carbon dioxide (CO2) and methane (CH4) by human activities will increase global atmospheric CO2 and CH4 concentrations and surface temperature significantly. Fields of paddy rice, the most important form of anthropogenic wetlands, account for about 9% of anthropogenic sources of CH4. Elevated atmospheric CO2 may enhance CH4 production in rice paddies, potentially reinforcing the increase in atmospheric CH4. However, what is not known is whether and how elevated CO2 influences CH4 consumption under anoxic soil conditions in rice paddies, as the net emission of CH4 is a balance of methanogenesis and methanotrophy. In this study, we used a long-term free-air CO2 enrichment experiment to examine the impact of elevated CO2 on the transformation of CH4 in a paddy rice agroecosystem. We demonstrate that elevated CO2 substantially increased anaerobic oxidation of methane (AOM) coupled to manganese and/or iron oxides reduction in the calcareous paddy soil. We further show that elevated CO2 may stimulate the growth and metabolism of Candidatus Methanoperedens nitroreducens, which is actively involved in catalyzing AOM when coupled to metal reduction, mainly through enhancing the availability of soil CH4. These findings suggest that a thorough evaluation of climate-carbon cycle feedbacks may need to consider the coupling of methane and metal cycles in natural and agricultural wetlands under future climate change scenarios. 相似文献
18.
JIANWEN ZOU YAO HUANG† YANMEI QIN SHUWEI LIU QIRONG SHEN GENXING PAN YANYU LU‡ QIAOHUI LIU§ 《Global Change Biology》2009,15(1):229-242
Nitrogen fertilizer‐induced direct nitrous oxide (N2O) emissions depend on water regimes in paddy fields, such as seasonal continuous flooding (F), flooding–midseason drainage–reflooding (F‐D‐F), and flooding–midseason drainage–reflooding–moist intermittent irrigation but without water logging (F‐D‐F‐M). In order to estimate the changes in direct N2O emission from paddy fields during the rice‐growing season in Mainland of China between the 1950s and the 1990s, the country‐specific emission factors of N2O‐N under different water regimes combined with rice production data were adopted in the present study. Census statistics on rice production showed that water management and nitrogen input regimes have changed in rice paddies since the 1950s. During the 1950s–1970s, about 20–25% of the rice paddy was continuously waterlogged, and 75–80% under the water regime of F‐D‐F. Since the 1980s, about 12–16%, 77%, and 7–12% of paddy fields were under the water regimes of F, F‐D‐F, and F‐D‐F‐M, respectively. Total nitrogen input during the rice‐growing season has increased from 87.5 kg N ha−1 in the 1950s to 224.6 kg N ha−1 in the 1990s. The emission factors of N2O‐N were estimated to be 0.02%, 0.42%, and 0.73% for rice paddies under the F, F‐D‐F, and F‐D‐F‐M water regimes, respectively. Seasonal N2O emissions have increased from 9.6 Gg N2O‐N each year in the 1950s to 32.3 Gg N2O‐N in the 1990s, which is accompanied by the increase in rice yield over the period 1950s–1990s. The uncertainties in N2O estimate were estimated to be 59.8% in the 1950s and 37.5% in the 1990s. In the 1990s, N2O emissions during the rice‐growing season accounted for 8–11% of the reported annual total of N2O emissions from croplands in China, suggesting that paddy rice development could have contributed to mitigating agricultural N2O emissions in the past decades. However, seasonal N2O emissions would be increased, given that saving‐water irrigation and nitrogen inputs are increasingly adopted in rice paddies in China. 相似文献
19.
Senthilkumar V Busby SJ Gunasekaran P Senthikumar V Bushby SJ 《Biotechnology letters》2003,25(19):1653-1656
Levansucrase is responsible for levan formation during sucrose fermentation of Zymomonas mobilis, and this decreases the efficiency of ethanol production. As thiol modifying agents decrease levan formation, a role for cysteine residues in levansucrase activity has been examined using derivatives of Z. mobilis levansucrase that carry serine substitutions of cysteine at positions 121, 151 or 244. These substitutions abolished the levan forming activity of levansucrase whilst only halving its activity in sucrose hydrolysis. Thus, polymerase and hydrolase activities of Z. mobilis levansucrase are separate and have different requirements for the enzyme's cysteine residues. 相似文献
20.
《Inorganica chimica acta》2006,359(7):2309-2313
Deprotonated 3-(2-fluorophenyl)-1-(4-acetylphenyl)triazene reacts with Hg(CH3COO)2 in tetrahydrofuran to give light yellow crystals of [HgII(RPhNNNPhR′)2]n (R = acetyl, R′ = F). The new polymeric triazenide complex of Hg(II) belongs to the monoclinic space group C2/c. The lattice of [HgII(RPhNNNPhR′)2]n can be viewed as a bidimensional assembly of planar tectons [HgII(RPhNNNPhR′)2], occurring through metallocene alike Hg(II)-η2,η2-arene π-interactions along the crystallographic axis b and non classical C-H?O bonding along the axis a. 相似文献