Mother–embryo isotope (δ15N, δ13C) fractionation and mercury (Hg) transfer in aplacental deep‐sea sharks

Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopic values and total mercury (Hg) concentrations were analysed in muscle and liver of mothers and embryos of two aplacental shark species, Squalus megalops and Centrophorus moluccensis. Embryos of the two species had similar or lower isotopic values than their respective mothers, the only exception being for δ¹³C, which was higher in the liver of C. moluccensis embryos than in their mothers. Hg concentrations were systematically lower in embryos compared with their mothers suggesting a low transfer of this element in muscle and liver.     

Controls on water balance of shallow thermokarst lakes and their relations with catchment characteristics: a multi‐year,landscape‐scale assessment based on water isotope tracers and remote sensing in Old Crow Flats,Yukon (Canada)

Many northern lake‐rich regions are undergoing pronounced hydrological change, yet inadequate knowledge of the drivers of these landscape‐scale responses hampers our ability to predict future conditions. We address this challenge in the thermokarst landscape of Old Crow Flats (OCF) using a combination of remote sensing imagery and monitoring of stable isotope compositions of lake waters over three thaw seasons (2007–2009). Quantitative analysis confirmed that the hydrological behavior of lakes is strongly influenced by catchment vegetation and physiography. Catchments of snowmelt‐dominated lakes, typically located in southern peripheral areas of OCF, encompass high proportions of woodland/forest and tall shrub vegetation (mean percent land cover = ca. 60%). These land cover types effectively capture snow and generate abundant snowmelt runoff that offsets lake water evaporation. Rainfall‐dominated lakes that are not strongly influenced by evaporation are typically located in eastern and northern OCF where their catchments have higher proportions of dwarf shrub/herbaceous and sparse vegetation (ca. 45%), as well as surface water (ca. 20%). Evaporation‐dominated lakes, are located in the OCF interior where their catchments are distinguished by substantially higher lake area to catchment area ratios (LA/CA = ca. 29%) compared to low evaporation‐influenced rainfall‐dominated (ca. 10%) and snowmelt‐dominated (ca. 4%) lakes. Lakes whose catchments contain >75% combined dwarf shrub/herbaceous vegetation and surface water are most susceptible to evaporative lake‐level drawdown, especially following periods of low precipitation. Findings indicate that multiple hydrological trajectories are probable in response to climate‐driven changes in precipitation amount and seasonality, vegetation composition, and thermokarst processes. These will likely include a shift to greater snowmelt influence in catchments experiencing expansion of tall shrubs, greater influence from evaporation in catchments having higher proportions of surface water, and an increase in the rate of thermokarst lake expansion and probability of drainage. Local observations suggest that some of these changes are already underway.     

Isotope labelling of Rubisco subunits provides in vivo information on subcellular biosynthesis and exchange of amino acids between compartments

The architecture of plant metabolism includes substantial duplication of metabolite pools and enzyme catalyzed reactions in different subcellular compartments. This poses challenges for understanding the regulation of metabolism particularly in primary metabolism and amino acid biosynthesis. To explore the extent to which amino acids are made in single compartments and to gain insight into the metabolic precursors from which they derive, we used steady state (13) C labelling and analysed labelling in protein amino acids from plastid and cytosol. Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) is a major component of green tissues and its large and small subunits are synthesized from different pools of amino acids in the plastid and cytosol, respectively. Developing Brassica napus embryos were cultured in the presence of [U-(13) C]-sucrose, [U-(13) C]-glucose, [U-(13) C]-glutamine or [U-(13) C]-alanine to generate proteins. The large subunits (LSU) and small subunits (SSU) of Rubisco were isolated and the labelling in their constituent amino acids was analysed by gas chromatography-mass spectrometry. Amino acids including alanine, glycine and serine exhibited different (13) C enrichment in the LSU and SSU, demonstrating that these pools have different metabolic origins and are not isotopically equilibrated between the plastid and cytosol on the time scale of cellular growth. Potential extensions of this novel approach to other macromolecules, organelles and cell types of eukaryotes are discussed.     

Using stable isotopes to trace long-distance dispersal in birds and other taxa

The study of long‐distance dispersal (LDD) in animals may be advanced by recent applications of stable isotope analyses designed to track migratory organisms and to link populations throughout their annual cycle. This approach depends on there being enough isotopic difference in tissues among potential source populations such that individuals can be unequivocally assigned to their source. The isotopic mapping of such populations will be feasible only for species occurring in relatively few disjunct populations. However, the identification of isotopic outliers within known populations will be an extremely useful first step in the forensic application of stable isotopes to identify dispersal in general, and LDD in particular. The use of deuterium isotope analysis (δD) of tissues that can be assigned to its source (e.g. feather moult or its hair growth location) has provided a recent breakthrough in our ability to associate individuals with geographical origins at continental scales. The combination of this stable isotope with others and the ultimate combination of a variety of techniques, including the measurement of trace elements and molecular genetics markers, will undoubtedly improve resolution. The isotopic cataloguing of known history (i.e. philopatric) individuals within populations will be an important step in applying isotope techniques to evaluating LDD in any species. For aquatic insects, the isotopic marking of large numbers of individuals is possible through isotopic enrichment of local food webs using labelled compounds.     

Metabolic flux analysis in Escherichia coli by integrating isotopic dynamic and isotopic stationary 13C labeling data

The novel concept of isotopic dynamic 13C metabolic flux analysis (ID-13C MFA) enables integrated analysis of isotopomer data from isotopic transient and/or isotopic stationary phase of a 13C labeling experiment, short-time experiments, and an extended range of applications of 13C MFA. In the presented work, an experimental and computational framework consisting of short-time 13C labeling, an integrated rapid sampling procedure, a LC-MS analytical method, numerical integration of the system of isotopomer differential equations, and estimation of metabolic fluxes was developed and applied to determine intracellular fluxes in glycolysis, pentose phosphate pathway (PPP), and citric acid cycle (TCA) in Escherichia coli grown in aerobic, glucose-limited chemostat culture at a dilution rate of D = 0.10 h(-1). Intracellular steady state concentrations were quantified for 12 metabolic intermediates. A total of 90 LC-MS mass isotopomers were quantified at sampling times t = 0, 91, 226, 346, 589 s and at isotopic stationary conditions. Isotopic stationarity was reached within 10 min in glycolytic and PPP metabolites. Consistent flux solutions were obtained by ID-13C MFA using isotopic dynamic and isotopic stationary 13C labeling data and by isotopic stationary 13C MFA (IS-13C MFA) using solely isotopic stationary data. It is demonstrated that integration of dynamic 13C labeling data increases the sensitivity of flux estimation, particularly at the glucose-6-phosphate branch point. The identified split ratio between glycolysis and PPP was 55%:44%. These results were confirmed by IS-13C MFA additionally using labeling data in proteinogenic amino acids (GC-MS) obtained after 5 h from sampled biomass.     

N-terminal cysteinyl proteins can be prepared using thrombin cleavage

Expressed protein ligation--which allows native proteins to be selectively linked together by a normal peptide bond in an aqueous environment--has emerged as a powerful technique. The technique requires the formation of a C-terminal alpha-thioester and an N-terminal Cys. An N-terminal Cys can be formed by enzymatic cleavage, commonly using the Factor Xa and TEV proteases. We show that thrombin can be used for the formation of N-terminal Cys, providing another choice of reagents for expressed protein ligation. Proteins with N-terminal Cys can be obtained by the convenient modification of vectors with the putative thrombin cleavage site LVPRG to LVPRC. Two example protein domains (Csk and Abl tyrosine kinase domain) with N-terminal Cys are demonstrated using this method. The use of thrombin protease to generate N-terminal Cys overcomes some of the limitations of existing methods, making it generally useful for expressed protein ligation and other biotechnological applications.     

Applications of stable isotope analyses to avian ecology

In the past 20 years the use of stable isotope analysis has become increasingly common in ecological studies. In fact, in some instances these techniques have yielded remarkable insights into the foraging preferences and migrations of birds. Despite these advances and the potential of the approach, it is possibly still not as widely used as might be expected. In this paper we aim to illustrate the potential of the approach in the hope of encouraging more avian ecologists to think again about how these techniques might provide insights in the systems on which they work. We discuss some of the principles behind the approach, and review some of the more recent ornithological studies that have used stable isotope techniques to trace trophic pathways or infer migratory origins. We follow this by discussing some of the latest ideas on how stable isotopes may be used to generate community metrics and close by detailing the important assumptions and caveats that should be considered before undertaking any studies using this technique.     

同位素示踪技术在光合作用研究中的应用

利用同位素示踪技术可以掌握物质在化学反应中运行和变化情况。试论述同位素示踪技术在研究光合作用中的多种应用：提示光合作用中几种元素的转变方向;判断光合作用的反应场所和反应条件;推断光合作用的反应过程;检验产物的运输方向;研究光合作用与呼吸作用的关系。     

Protonless 13C direct detection NMR: characterization of the 37 kDa trimeric protein CutA1

The major limitation of nuclear magnetic resonance spectroscopy arises from the increase of nuclear transverse relaxation rates with increasing molecular mass. This causes reduction in spectral resolution and coherence transfer efficiency. The use of 2H-labeling to eliminate 1H-mediated relaxation pathways and the constructive use of cross correlation effects (TROSY, CRINEPT) alleviate the phenomenon. An alternative approach is to use direct detection of heteronuclei. Specifically designed 13C direct detection experiments can complement the set of 1H-based NMR experiments commonly used for structure determination providing an additional source of information less affected by the detrimental transverse relaxation effect. We applied this novel methodology to the study of the CutA1 protein (12.3 kDa) from E. coli that forms a homotrimer in solution with a total molecular mass of 37 kDa. In this work we demonstrate that the information available from 13C direct detection experiments makes it possible to completely assign the NMR resonances of the backbone of this 37 kDa trimeric protein without the need of deuteration. The structural and dynamical knowledge obtained for this system may contribute to understand its biological role.     

铵盐和硝酸盐稳定同位素丰度测定方法及其应用案例

综述了过去几十年来铵盐和硝酸盐稳定同位素丰度测定方法的历史发展变化,分析了各种方法的优缺点,并对新方法作了介绍和推荐.目前铵盐稳定同位素丰度的最新测定方法为次溴酸盐氧化结合羟胺还原法,硝酸盐氮氧同位素丰度主流的测定方法为反硝化细菌法和镉粉叠氮酸还原化学法.这些方法的主要共同特点是以N₂O为分析物,分析精度高,对样品的含氮量需求小,一般只需要10～60 nmol N,适用于低浓度样品.新方法的建立对于国内外开展氮素循环研究将起到极大的推动作用.