Need for revisiting the terminology about speciation

International audienceᅟThe term speciation is used for over 30 years, with different meanings. In the early 2000s, a reference definition was proposed. The elemental distribution is discussed only with respect to molecular structures. Polytatomic entities such as amorphous or crystalline structures, dispersed in a liquid or gas, or in the solid phase, are not taken into account. The distribution of the element, both at the interfaces and in the solids, is not yet considered. This editorial discusses the limitations of this definition and its consequences. The different terminologies proposed from the reference definition are also discussed. Given all these considerations, it is proposed that speciation is considered as a description of the physical and chemical characteristics of an element. This description should be given from the atomic scale of this element to the scale of the surrounding medium, in the continuum of size, from the dissolved or gaseous phase to the solid phases. © 2016, Springer-Verlag Berlin Heidelberg

CZE ICP MS separation of metallothioneins in human brain cytosols comparability of electropherograms obtained from different sample matrices

Capillary zone electrophoresis, with its high resolution capability in the separation of different compounds, is well suited for the investigation of metal containing proteins, especially when elemental detection is conducted using hyphenated inductively coupled plasma mass spectrometry. A major problem in the separation of proteins in body fluids is caused by the effects of different sample matrix composition. The migration time of proteins varies significantly, depending on the nature of the matrix. Electropherograms are consequently difficult to compare and the peak identification is uncertain. Pre analytical steps for the reduction of matrix compounds enhance the quality of the data, but the results are still unsatisfactory. This paper describes a technique for obtaining electropherograms that can be used for comparison purposes by correction of the data with the aid of time markers. A mixture of five substances caesium chloride, arsenocholine, arsenobetaine, dimethylarsinic acid and monomethylarsonic acid was added in a separate injection step. Ionic caesium eluted at the start of the separation and the other four markers appeared throughout and at the end of the electropherogram. All electropherograms were normalized to a reference run by recalculation of the time axis using the time markers. The method was applied to the analysis of human brain cytosols. Samples were separated after different pre treatment steps and were compared, with special emphasis on the detection of the isoform metallothionein

High spatial resolution imaging of subcellular macro and trace element distribution during phagocytosis

The bioavailability of trace elements in the course of evolution had an essential influence on the emergence of life itself. This is reflected in the co-evolution between eukaryotes and prokaryotes. In this study, the influence and cellular distribution of bioelements during phagocytosis at the host-pathogen interface were investigated using high-resolution nanoscale secondary ion mass spectrometry (NanoSIMS) and quantitative inductively coupled plasma mass spectrometry. In the eukaryotic murine macrophages (RAW 264.7 cell line), the cellular Fe/Zn ratio was found to be balanced, whereas the dominance of iron in the prokaryotic cells of the pathogen Salmonella enterica Serovar Enteritidis was ∼90% compared to zinc. This confirms the evolutionary increased zinc requirement of the eukaryotic animal cell. Using NanoSIMS, the Cs+ primary ion source allowed high spatial resolution mapping of cell morphology down to the subcellular level. At a comparable resolution, several low-abundant trace elements could be mapped during phagocytosis with a RF plasma O- primary ion source. An enrichment of copper and nickel could be detected in the prokaryotic cells. Surprisingly, an accumulation of cobalt in the area of the nuclear envelope was observed, indicating an interesting but still unknown distribution of this trace element in murine macrophages. © The Author(s) 2022. Published by Oxford University Press

On-line isotope dilution in laser ablation inductively coupled plasma mass spectrometry using a microflow nebulizer inserted in the laser ablation chamber

Laser ablation ICP-MS (inductively coupled plasma mass spectrometry) is becoming one of the most important analytical techniques for fast determination of trace impurities in solid samples. Quantification of analytical results requires matrix-matched standards, which are in some cases (e.g., high-purity metals, proteins separated by 2D gel electrophoresis) difficult to obtain or prepare. In order to overcome the quantification problem a special arrangement for on-line solution-based calibration has been proposed in laser ablation ICP-MS by the insertion of a microflow nebulizer in the laser ablation chamber. This arrangement allows an easy, accurate and precise quantification by on-line isotope dilution using a defined standard solution with an isotope enriched tracer nebulized to the laser-ablated sample material. An ideal matrix matching in LA-ICP-MS is therefore obtained during the measurement. The figures of merit of this arrangement with a microflow nebulizer inserted in the laser ablation chamber and applications of on-line isotope dilution in LA-ICP-MS on two different types of sample material (NIST glass SRM 612 and NIST apple leaves SRM 1515) will be described. (c) 2005 Elsevier B.V. All rights reserved

Towards an Understanding of the Function of the Phytochelatin Synthase of Schistosoma mansoni

International audiencePhytochelatin synthase (PCS) is a protease-like enzyme that catalyzes the production of metal chelating peptides, the phytochelatins, from glutathione (GSH). In plants, algae, and fungi phytochelatin production is important for metal tolerance and detoxification. PCS proteins also function in xenobiotic metabolism by processing GSH S-conjugates. The aim of the present study is to elucidate the role of PCS in the parasitic worm Schistosoma mansoni. Recombinant S. mansoni PCS proteins expressed in bacteria could both synthesize phytochelatins and hydrolyze various GSH S-conjugates. We found that both the N-truncated protein and the N- and C-terminal truncated form of the enzyme (corresponding to only the catalytic domain) work through a thiol-dependant and, notably, metal-independent mechanism for both transpeptidase (phytochelatin synthesis) and peptidase (hydrolysis of GSH S-conjugates) activities. PCS transcript abundance was increased by metals and xenobiotics in cultured adult worms. In addition, these treatments were found to increase transcript abundance of other enzymes involved in GSH metabolism. Highest levels of PCS transcripts were identified in the esophageal gland of adult worms. Taken together, these results suggest that S. mansoni PCS participates in both metal homoeostasis and xenobiotic metabolism rather than metal detoxification as previously suggested and that the enzyme may be part of a global stress response in the worm. Because humans do not have PCS, this enzyme is of particular interest as a drug target for schistosomiasis. © 2013 Rigouin et al

Peptide labeling with lanthanide-NHS-ester-DOTA investigated by nano-HPLC

International audienceLabeling of peptides and proteins using chelators binding metal ions has become a novel approach for quantitative proteomics in recent years. The aim of this work was the optimization of a new method for peptide derivatization with lanthanide labels (holmium, lutetium, and thulium) followed by nano high performance liquid chromatography (nano-HPLC) separation with UV detection. Matrix-assisted laser desorption ionization-mass spectrometry (MALDI MS) was used to confirm the derivatization and to identify the derivatized peptides. Peptides were labeled with the three different lanthanide metals using a bifunctional DOTA-based (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) reagent. The results demonstrate that the derivatization reaction using the chelating reagent DOTA-NHS-ester was effective for single peptides and peptide mixtures. Furthermore, an efficient pre-cleaning method was applied by nano-HPLC using a C-18 trap column for elimination of the excess of labeling reagent. The application of the optimized method to label peptides in a Cytochrome C digest delivered comparable results to those obtained with model peptides. © 2014 Elsevier B.V

Chemical bioimaging for the subcellular localization of trace elements by high contrast TEM, TEM/X-EDS, and NanoSIMS

International audienceChemical bioimaging offers an important contribution to the investigation of biochemical functions, biosorption and bioaccumulation processes of trace elements via their localization at the cellular and even at the subcellular level. This paper describes the combined use of high contrast transmission electron microscopy (HC-TEM), energy dispersive X-ray spectroscopy (X-EDS), and nano secondary ion mass spectrometry (NanoSIMS) applied to a model organism, the unicellular green algae Chlamydomonas reinhardtii. HC-TEM providing a lateral resolution of 1 nm was used for imaging the ultrastructure of algae cells which have diameters of 5–10 μm. TEM coupled to X-EDS (TEM/X-EDS) combined textural (morphology and size) analysis with detection of Ca, P, K, Mg, Fe, and Zn in selected subcellular granules using an X-EDS probe size of approx. 1 μm. However, instrumental sensitivity was at the limit for trace element detection. NanoSIMS allowed chemical imaging of macro and trace elements with subcellular resolution (element mapping). Ca, Mg, and P as well as the trace elements Fe, Cu, and Zn present at basal levels were detected in pyrenoids, contractile vacuoles, and granules. Some metals were even localized in small vesicles of about 200 nm size. Sensitive subcellular localization of trace metals was possible by the application of a recently developed RF plasma oxygen primary ion source on NanoSIMS which has shown good improvements in terms of lateral resolution (below 50 nm), sensitivity, and stability. Furthermore correlative single cell imaging was developed combining the advantages of TEM and NanoSIMS. An advanced sample preparation protocol provided adjacent ultramicrotome sections for parallel TEM and NanoSIMS analyses of the same cell. Thus, the C. reinhardtii cellular ultrastructure could be directly related to the spatial distribution of metals in different cell organelles such as vacuoles and chloroplast. © 2016 Elsevier Gmb