Lanthanum-fluoride electrode-based methods to monitor fluoride transport in cells and reconstituted lipid vesicles.

Fluoride (F-) export proteins, including F- channels and F- transporters, are widespread in biology. They contribute to cellular resistance against fluoride ion, which has relevance as an ancient xenobiotic, and in more modern contexts like organofluorine biosynthesis and degradation or dental medicine. This chapter summarizes quantitative methods to measure fluoride transport across membranes using fluoride-specific lanthanum-fluoride electrodes. Electrode-based measurements can be used to measure unitary fluoride transport rates by membrane proteins that have been purified and reconstituted into lipid vesicles, or to monitor fluoride efflux into living microbial cells. Thus, fluoride electrode-based measurements yield quantitative mechanistic insight into one of the major determinants of fluoride resistance in microorganisms, fungi, yeasts, and plants.

Assessment of osteopontin as an early nephrotoxicity indicator in human renal proximal tubule cells and its application in evaluating lanthanum-induced nephrotoxicity.

Nephrotoxicity is a common adverse effect induced by various chemicals, necessitating the development of reliable toxicity screening models for nephrotoxicity assessment. In this study, we assessed a group of nephrotoxicity indicators derived from different toxicity pathways, including conventional endpoints and kidney tubular injury biomarkers such as clusterin (CLU), kidney injury molecule-I (KIM-1), osteopontin (OPN), and neutrophil gelatinase-associated lipocalin (NGAL), using HK-2 and induced pluripotent stem cells (iPSCs)-derived renal proximal tubular epithelial-like cells (PTLs). Among the biomarkers tested, OPN emerged as the most discerning and precise marker. The predictive potential of OPN was tested using a panel of 10 nephrotoxic and 5 non-nephrotoxic compounds. The results demonstrated that combining OPN with the half-maximal inhibitory concentration (IC50) enhanced the diagnostic accuracy in both cellular models. Additionally, PTLs cells showed superior predictive efficacy for nephrotoxicity compared to HK-2 cells in this investigation. The two cellular models were utilized to evaluate the nephrotoxicity of lanthanum. The findings indicated that lanthanum possesses nephrotoxic properties; however, the degree of nephrotoxicity was relatively low, consistent with the outcomes of in vivo experiments.

The Effect of Lanthanum (III) Nitrate on the Osteogenic Differentiation of Mice Bone Marrow Stromal Cells.

To study the species of lanthanum (III) nitrate (La[NO3]3) dispersed in cell media and the effect on the osteoblast differentiation of bone marrow stroma cells (BMSCs). Different La-containing precipitations were obtained by adding various concentrations of La(NO3)3 solutions to Dulbecco's modified Eagle medium (DMEM) or DMEM with fetal bovine serum (FBS). A series of characterisation methods, including dynamic light scattering, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and protein quantification were employed to clarify the species of the different La-containing precipitations. The primary BMSCs were isolated, and the cell viability, alkaline phosphatase activity, and the formation of a mineralised nodule of BMSCs were tested when treated with different La-containing precipitations. The La(NO3)3 solutions in DMEM could form LaPO4, which exits in the particle formation, while the La(NO3)3 solutions in DMEM with FBS could form a La-PO4-protein compound. When treated with La(NO3)3 solutions in DMEM, the cell viability of the BMSCs was inhibited at the concentrations of 1, 10, and 100 µM at 1 day and 3 days. Meanwhile, the supernatant derived from the La(NO3)3 solutions in DMEM did not affect the cell viability of the BMSCs. In addition, the precipitate derived from the La(NO3)3 solutions in DMEM added to the complete medium inhibited the cell viability of the BMSCs at concentrations of 10 µM and 100 µM. When treated with La(NO3)3 solutions in DMEM with FBS, the derived precipitate and supernatant did not affect the cell viability of the BMSCs, except for the concentration of 100 µM La(NO3)3. The La-PO4-protein formed from the La(NO3)3 solutions in DMEM with FBS inhibited the osteoblast differentiation of BMSCs at the concentration of 1 µM La(NO3)3 (P < 0.05) but had no effect on either the osteoblast differentiation at the concentrations of 0.001 and 0.1 µM or on the formation of a mineralised nodule at all tested concentrations of La(NO3)3. Overall, La(NO3)3 solutions in different cell culture media could form different La-containing compounds: La-PO4 particles (in DMEM) and a La-PO4-protein compound (in DMEM with FBS). The different La-containing compounds caused different effects on the cell viability, osteoblast differentiation, and the formation of a mineralised nodule of the BMSCs. The La-containing precipitation inhibited the osteoblast differentiation by inhibiting the expression of osteoblast-related genes and proteins, providing a theoretical basis for clinical doctors to apply phosphorus-lowering drugs such as lanthanum carbon.

Biodegradation enhancement of high concentrations formaldehyde waste gas and verification of the metabolic mechanism.

The enhanced effects of formaldehyde biodegradation in a biofilm packing tower are investigated in this study. Three experimental groups were established: a blank control group, a biochar addition group, and a lanthanum addition group. The inlet gas flow rate, the inlet gas concentration, and the structural succession characteristics of the microbial community in the tower were investigated by regular sampling. The intracellular metabolites and key enzymes of the dominant functional bacteria, Pseudomonas P1 and Methylobacterium Q1, in the tower were analyzed. The results indicated that with the biochar addition, the formaldehyde purification efficiency increased significantly from 91.67-94.67 % to 94.12 96.85 %, and the bio-elimination capacity increased with an increase in the inlet gas flow rate from 2.314 to 13.988 mg L-1h-1 to 2.697-15.051 mg L-1h-1. With the addition of lanthanum, the purification efficiency increased significantly from 90.80-93.98 % to 94.36-96.78 %, and the bio-elimination capacity increased with an increase in the inlet gas concentration from 1.099-11.284 mg L-1h-1 to 1.266-11.961 mg L-1h-1. The microbial community structure in the tower changed with system operation, and the formaldehyde degrading functional bacteria formed the dominant bacteria. It was verified that P1 and Q1 metabolized high concentrations of formaldehyde by the serine cycle and the ribulose monophosphate (RuMP) cycle.

Determination of the distribution of rare earth elements La and Gd in Daphnia magna via micro and nano-SXRF imaging.

While our awareness of the toxicity of rare earth elements to aquatic organisms increases, our understanding of their direct interaction and accumulation remains limited. This study describes the acute toxicity of lanthanum (La) and gadolinium (Gd) in Daphnia magna neonates and discusses potential modes of action on the basis of the respective patterns of biodistribution. Ecotoxicological bioassays for acute toxicity were conducted and dissolved metal concentrations at the end of the tests were determined. The results showed a significant difference in nominal EC50 (immobility) between La (>30 mg L-1) and Gd (13.93 (10.92 to 17.38) mg L-1). Daphnids that were then exposed to a concentration close to the determined EC50 of Gd (15 mg L-1, nominal concentration) for 48 h and 72 h were studied by synchrotron micro and nano-X-ray fluorescence to evaluate the biodistribution of potentially accumulated metals. X-ray fluorescence analyses showed that La was mainly found in the intestinal track and appeared to accumulate in the hindgut. This accumulation might be explained by the ingestion of solid La precipitates formed in the media. In contrast, Gd could only be detected in a small amount, if at all, in the intestinal tract, but was present at a much higher concentration in the tissues and became more pronounced with longer exposure time. The solubility of Gd is higher in the media used, leading to higher dissolved concentrations and uptake into tissue in ionic form via common metal transporting proteins. By studying La and Gd biodistribution in D. magna after an acute exposure, the present study has demonstrated that different uptake pathways of solid and dissolved metal species may lead to different accumulation patterns and toxicity.

Lanpepsy is a novel lanthanide-binding protein involved in the lanthanide response of the obligate methylotroph Methylobacillus flagellatus.

Lanthanides were recently discovered as metals required in the active site of certain methanol dehydrogenases. Since then, the characterization of the lanthanome, that is, proteins involved in sensing, uptake, and utilization of lanthanides, has become an active field of research. Initial exploration of the response to lanthanides in methylotrophs has revealed that the lanthanome is not conserved and that multiple mechanisms for lanthanide utilization must exist. Here, we investigated the lanthanome in the obligate model methylotroph Methylobacillus flagellatus. We used a proteomic approach to analyze differentially regulated proteins in the presence of lanthanum. While multiple known proteins showed induction upon growth in the presence of lanthanum (Xox proteins, TonB-dependent receptor), we also identified several novel proteins not previously associated with lanthanide utilization. Among these was Mfla_0908, a periplasmic 19 kDa protein without functional annotation. The protein comprises two characteristic PepSY domains, which is why we termed the protein lanpepsy (LanP). Based on bioinformatic analysis, we speculated that LanP could be involved in lanthanide binding. Using dye competition assays, quantification of protein-bound lanthanides by inductively coupled plasma mass spectrometry, as well as isothermal titration calorimetry, we demonstrated the presence of multiple lanthanide binding sites that showed selectivity over the chemically similar calcium ion. LanP thus represents the first member of the PepSY family that binds lanthanides. Although the physiological role of LanP is still unclear, its identification is of interest for applications toward the sustainable purification and separation of rare-earth elements.

Regulatory actions of rare earth elements (La and Gd) on the cell cycle of root tips in rice seedlings (Oryza sativa L.).

The continuous expansion of the application of rare earth elements (REEs) in various fields has attracted attention to their biosafety. At present, the molecular mechanisms underlying the biological effects of REEs are unclear. In this study, the effects of lanthanum (La) and gadolinium (Gd) on cell cycle progression in the root tips of rice seedlings were investigated. Low concentrations of REEs (0.1 mg L-1) induced an increase in the number of cells in the prophase and metaphase, while high concentrations of REEs (10 mg L-1) induced an increase in the number of cells in the late and terminal stages of the cell cycle, and apoptosis or necrosis. Additionally, low concentrations of REEs induced a significant increase in the expression of the cell cycle factors WEE1, CDKA;1, and CYCB1;1, and promoted the G2/M phase and accelerated root tip growth. However, at high REEs concentrations, the DNA damage response sensitized by BRCA1, MRE11, and TP53 could that prevent root tip growth by inhibiting the transcription factor E2F, resulting in obvious G1/S phase transition block and delayed G2/M phase conversion. Furthermore, by comparing the biological effect mechanisms of La and Gd, we found that these two REEs share regulatory actions on the cell cycle of root tips in rice seedlings.

Do climate change related factors modify the response of Mytilus galloprovincialis to lanthanum? The case of temperature rise.

Most of the electric and electronic waste is not recycled and the release of its components into the environment is expected, including the rare-earth element Lanthanum (La), which has already been reported in the aquatic systems. Furthermore, considering climate change factors such as the predicted increase in temperature, the susceptibility of aquatic organisms to these rare elements may be modified. In light of this, the present study aimed to evaluate the relevance of temperature on La-derived effects in the mussel Mytilus galloprovincialis. Several biomarkers and La bioaccumulation were assessed in organisms exposed to 0 (control) and 10 µg/L of La at two distinct temperatures (17 and 22 °C) for 28 days. Results showed that temperature did not influence La bioaccumulation in mussels. However, exposure to La resulted in a decreased metabolic capacity and an enhancement of biotransformation enzymes activity, as a possible defense behavior of mussels to avoid La accumulation and toxicity. Nevertheless, antioxidant defenses were also inhibited leading to increased lipid peroxidation (LPO) levels. Warming alone seemed to cause a metabolic shutdown seen as reduced enzyme activities and protein carbonylation (PC) levels. Simultaneous La exposure and temperature rise caused combined effects on mussels, as they accused metabolic depression, biotransformation defenses activation, antioxidant capacity reduction, and higher cellular damage. Overall, this study highlights the need to perform environmental risk assessment studies, by considering emerging contaminants exposures at relevant concentrations, both at present and forecasted climate change scenarios.

Biochemical alterations caused by lanthanum and gadolinium in Mytilus galloprovincialis after exposure and recovery periods.

The increasing use of rare earth elements (REEs) in electric and electronic equipment has been associated with the presence of these elements in aquatic systems. The present study aimed to evaluate the toxicity of two REEs, Lanthanum (La) and Gadolinium (Gd), towards the mussel species Mytilus galloprovincialis. For this, the toxicity was assessed after a short-term exposure (14 days) to an environmentally relevant concentration of each element (10 µg/L), followed by a recovery period (14 days) in the absence of any contaminant. The measured biomarkers included energy-related parameters, activity of antioxidant and biotransformation enzymes, indicators of oxidative damage, levels of oxidized glutathione and neurotoxicity. After exposure mussels accumulated more La (0.54 µg/g) than Gd (0.15 µg/g). After recovery higher concentration decrease was observed for Gd (≈40% loss) compared to La exposed mussels (≈30% loss) which may be associated with lower detoxification capacity of mussels previously exposed to La. Mussels increased their metabolism (i.e., higher electron transport system activity) only after the exposure to Gd. Exposure to La and Gd resulted into lower energy expenditure, while when both elements were removed glycogen and protein concentrations decreased to values observed in non-contaminated mussels. Antioxidant and biotransformation capacity was mainly increased in the presence of Gd. This defense response avoided the occurrence of cellular damage but still loss of redox balance was found regardless the contaminant, which was re-established after the recovery period. Neurotoxicity was only observed in the presence of Gd with no effects after the recovery period. Results showed that a short-term exposure to La and especially to Gd can exert deleterious effects that may compromise specific biochemical pathways in aquatic species, such as M. galloprovincialis, but under low concentrations organisms can be able to re-establish their biochemical status to control levels after a recovery period.

Lanthanum Impairs Learning and Memory by Activating Microglia in the Hippocampus of Mice.

Lanthanum can induce neurotoxicity and impair cognitive function; therefore, research on the mechanism by which the ability to learning and memory is decreased by lanthanum is vitally important for protecting health. Microglia are a type of neuroglia located throughout the brain and spinal cord that play an important role in the central nervous system. When overactive, these cells can cause the excessive production of inflammatory cytokines that can damage neighboring neurons. The purpose of this study was to explore the effect of lanthanum in the form of lanthanum chloride (LaCl3) on learning and the memory of mice and determine whether there is a relationship between hippocampal neurons or learning and memory damage and excessive production of inflammatory cytokines. Four groups of pregnant Chinese Kun Ming mice were exposed to 0, 18, 36, or 72 mM LaCl3 in their drinking water during lactation. The offspring were then exposed to LaCl3 in the breast milk at birth until weaning and then exposed to these concentrations in their drinking water for 2 months after weaning. The results showed that LaCl3 impaired learning and memory in mice and injured their neurons, activated the microglia, and significantly overregulated the mRNA and protein expression of tumor necrosis factor alpha, interleukin (IL)-1ß, IL-6, monocyte chemoattractant protein-1, and nitric oxide in the hippocampus. The results of this study suggest that lanthanum can impair learning and memory in mice, possibly by over-activating the microglia.

Biological applications of green synthesized lanthanum oxide nanoparticles via Couroupita guianensis abul leaves extract.

In this work, extract from leaves of Couroupita guianensis (C.guianensis) abul was used as a potential reducing agent for the synthesis of lanthanum oxide (La2O3) nanoparticles (NPs). In addition, the morphology and several physicochemical properties of the La2O3 NPs were improved by introducing the ionic liquid of 1-butyl 3-methyl imidazolium tetra fluoroborate (BMIM BF4) as a stabilizing agent. The structure of the La2O3 (without ionic liquid) and IL-La2O3 (with ionic liquid) NPs were analyzed by X-ray diffraction (XRD). The chemical composition of the synthesized NPs was analyzed using the energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) studies. Optical and morphological studies were also performed. The antibacterial, antioxidant, anti-inflammatory, anti-diabetic and anticancer properties of the La2O3 and IL-La2O3 NPs were evaluated.

Effect of rare earth element lanthanum on lipid deposition and Wnt10b signaling in the liver of male zebrafish.

This paper investigates the effect of lanthanum (La) on lipid deposition and Wnt10b signaling in the liver of male zebrafish with exposure of 0, 10, 20, and 30 µmol/L La. It suggests that La can be accumulated in liver, and its treatments decrease the activities and gene expression of enzymes related to fatty acid synthesis. The levels of total cholesterol (TC), triglyceride (TG), and nonesterified fatty acids (NEFA) as well as the size of lipid droplets are decreased by La treatments. Moreover, La treatments affect the composition of fatty acids and the content of nutrient elements. Meanwhile, they also induce the gene expression of wnt10b, ß-catenin, pparα, and pparγ, but inhibit gsk-3ß gene expression in liver. Further study on the result of wnt10b gene interference shows that Wnt10b/ß-catenin signaling plays a crucial role in the regulatory process of hepatic lipid deposition. Taken together, our observations suggest that La accumulation affects lipid deposition in the liver of male zebrafish, and Wnt10b signaling pathway may be involved in this process.

Low-dose lanthanum activates endocytosis, aggravating accumulation of lanthanum or/and lead and disrupting homeostasis of essential elements in the leaf cells of four edible plants.

Rare earth elements (REEs) are emerging as a serious threat to ecological safety due to their increasing accumulation in environments. The accumulation of REEs in environments has significantly increased its accumulation in the leaves of edible plants. However, the accumulation pathway of REEs in the leaves of edible plants are still unknown. In this study, lanthanum [La(III), a widely used and accumulated REE] and four edible plants (soybean, lettuce, pakchoi, and celery) with short growth cycles were selected as research objects. By using interdisciplinary research techniques, we found that low-dose La(III) activated endocytosis (mainly the clathrin-mediated endocytosis) in the leaf cells of four edible plants, which provided an accumulation pathway for low-dose La in the leaf cells of these edible plants. The accumulation of La in the leaf cells was positively correlated with the intensity of endocytosis, while the intensity of endocytosis was negatively correlated with the density of leaf trichomes. In addition to the accumulation of La, low-dose La(III) also brought other risks. For example, the harmful element (Pb) can also be accumulated in the leaf cells via La(III)-activated endocytosis; the homeostasis of the essential elements (K, Ca, Fe, Mg) was disrupted, although the chlorophyll synthesis and the growth of these leaf cells were accelerated; and the expression of stress response genes (GmNAC20, GmNAC11) in soybean leaves was increased. These results provided an insight to further analyze the toxicity and mechanism of REEs in plants, and sounded the alarm for the application of REEs in agriculture.

Effect of nanomolar concentrations of lanthanum on Desmodesmus quadricauda cultivated under environmentally relevant conditions.

Toxicity of lanthanides is generally regarded as low, and they even have been suggested to be beneficial at low concentrations. This research was conducted to investigate effects of Lanthanum (La) on Desmodesmus quadricauda, a freshwater green microalga. The algal cultures were treated with nanomolar La concentrations under controlled environmentally relevant conditions. Intracellular localization of La was analyzed with µXRF tomography in frozen-hydrated samples. At sublethal concentration (128 nM) La was in hotspots inside the cells, while at lethal 1387 nM that led to release of other ions (K, Zn) from the cells, La filled most of the cells. La had no clear positive effects on growth or photosynthetic parameters, but increasing concentrations led to a dramatic decrease in cell counts. Chlorophyll fluorescence kinetic measurements showed that La led to the inhibition of photosynthesis. Maximal photochemical quantum yield of the PSII reaction center in dark-adapted state (Fv/Fm) decreased at > 4.3 nM La during the 2nd week of treatment. Minimum dark-adapted fluorescence quantum yield (F0) increased at > 13.5 nM La during the 2nd week of treatment except for control (0.2 nM La, baseline from chemicals) and 0.3 nM La. NPQ at the beginning of the actinic light phase showed significant increase for all the treatments. Metalloproteomics by HPLC-ICPMS showed that La binds to a >500 kDa soluble protein complex already in the sub-nM range of La treatments, in the low nM range to a small-sized (3 kDa) soluble peptide, and at >100 nM La additionally binds to a 1.5 kDa ligand.

Extracellular and Intracellular Lanthanide Accumulation in the Methylotrophic Beijerinckiaceae Bacterium RH AL1.

Recent work with Methylorubrum extorquens AM1 identified intracellular, cytoplasmic lanthanide storage in an organism that harnesses these metals for its metabolism. Here, we describe the extracellular and intracellular accumulation of lanthanides in the Beijerinckiaceae bacterium RH AL1, a newly isolated and recently characterized methylotroph. Using ultrathin-section transmission electron microscopy (TEM), freeze fracture TEM (FFTEM), and energy-dispersive X-ray spectroscopy, we demonstrated that strain RH AL1 accumulates lanthanides extracellularly at outer membrane vesicles (OMVs) and stores them in the periplasm. High-resolution elemental analyses of biomass samples revealed that strain RH AL1 can accumulate ions of different lanthanide species, with a preference for heavier lanthanides. Its methanol oxidation machinery is supposedly adapted to light lanthanides, and their selective uptake is mediated by dedicated uptake mechanisms. Based on transcriptome sequencing (RNA-seq) analysis, these presumably include the previously characterized TonB-ABC transport system encoded by the lut cluster but potentially also a type VI secretion system. A high level of constitutive expression of genes coding for lanthanide-dependent enzymes suggested that strain RH AL1 maintains a stable transcript pool to flexibly respond to changing lanthanide availability. Genes coding for lanthanide-dependent enzymes are broadly distributed taxonomically. Our results support the hypothesis that central aspects of lanthanide-dependent metabolism partially differ between the various taxa. IMPORTANCE Although multiple pieces of evidence have been added to the puzzle of lanthanide-dependent metabolism, we are still far from understanding the physiological role of lanthanides. Given how widespread lanthanide-dependent enzymes are, only limited information is available with respect to how lanthanides are taken up and stored in an organism. Our research complements work with commonly studied model organisms and showed the localized storage of lanthanides in the periplasm. This storage occurred at comparably low concentrations. Strain RH AL1 is able to accumulate lanthanide ions extracellularly and to selectively utilize lighter lanthanides. The Beijerinckiaceae bacterium RH AL1 might be an attractive target for developing biorecovery strategies to obtain these economically highly demanded metals in environmentally friendly ways.

Rare earth element lanthanum protects against atherosclerosis induced by high-fat diet via down-regulating MAPK and NF-κB pathways.

Rare earth elements, which are extensively used in environmental protection, medicine, food, aerospace and other fields, have attracted widespread attention in recent years. However, the effect on atherosclerosis and its biological mechanism remains unclear. To elucidate these problems, here we performed a study that Apolipoprotein E-deficient mice were fed with high-fat diet to promote the development of atherosclerosis, meanwhile, mice were received 0.1, 0.2, 1.0, 2.0 mg/kg lanthanum nitrate (La(NO3)3) for 12 weeks. The results showed that La(NO3)3 prominently inhibited aorta morphological alternations by histopathological examination. Meanwhile, La(NO3)3 regulated serum lipids, including reducing total cholesterol and increasing high-density lipoprotein. Moreover, the oxidative stress was alleviated by La(NO3)3 intervention through enhancing superoxide dismutase and glutathione, and decreasing malondialdehyde levels. In addition, enzyme-linked immunosorbent assay analysis showed La(NO3)3 could ameliorate the dysfunction of vascular endothelium with declined endothelin-1 and increased prostacyclin. Furthermore, Western blot analysis indicated that La(NO3)3 significantly down-regulated inflammation-mediated proteins including phosphorylated p38 mitogen-activated protein kinases (p-p38 MAPK), monocyte chemo-attractant protein, intercellular adhesion molecule-1, nuclear factor-kappa B p65 (NF-κB p65), tumor necrosis factor-α, interleukin-6 and interleukin-1ß, whereas up-regulated the inhibitor of NF-κB protein. In conclusion, La(NO3)3 ameliorates atherosclerosis by regulating lipid metabolism, oxidative stress, endothelial dysfunction and inflammatory response in mice. The potential mechanism associates with the inhibition of MAPK and NF-κB signaling pathways.

Effective binding of Tb3+ and La3+ cations on the donor side of Mn-depleted photosystem II.

The interaction of Tb3+ and La3+ cations with different photosystem II (PSII) membranes (intact PSII, Ca-depleted PSII (PSII[-Ca]) and Mn-depleted PSII (PSII[-Mn]) membranes) was studied. Although both lanthanide cations (Ln3+) interact only with Ca2+-binding site of oxygen-evolving complex (OEC) in PSII and PSII(-Ca) membranes, we found that in PSII(-Mn) membranes both Ln3+ ions tightly bind to another site localized on the oxidizing side of PSII. Binding of Ln3+ cations to this site is not protected by Ca2+ and is accompanied by very effective inhibition of Mn2+ oxidation at the high-affinity (HA) Mn-binding site ([Mn2+ + H2O2] couple was used as a donor of electrons). The values of the constant for inhibition of electron transport Ki are equal to 2.10 ± 0.03 µM for Tb3+ and 8.3 ± 0.4 µM for La3+, whereas OEC inhibition constant in the native PSII membranes is 323 ± 7 µM for Tb3+. The value of Ki for Tb3+ corresponds to Ki for Mn2+ cations in the reaction of diphenylcarbazide oxidation via HA site (1.5 µM) presented in the literature. Our results suggest that Ln3+ cations bind to the HA Mn-binding site in PSII(-Mn) membranes like Mn2+ or Fe2+ cations. Taking into account the fact that Mn2+ and Fe2+ cations bind to the HA site as trivalent cations after light-induced oxidation and the fact that Mn cation bound to the HA site (Mn4) is also in trivalent state, we can suggest that valency may be important for the interaction of Ln3+ with the HA site.

Enhancing Protein Electrospray Charge States by Multivalent Metal Ions: Mechanistic Insights from MD Simulations and Mass Spectrometry Experiments.

The structure and reactivity of electrosprayed protein ions is governed by their net charge. Native proteins in non-denaturing aqueous solutions produce low charge states. More highly charged ions are formed when electrospraying proteins that are unfolded and/or exposed to organic supercharging agents. Numerous studies have explored the electrospray process under these various conditions. One phenomenon that has received surprisingly little attention is the charge enhancement caused by multivalent metal ions such as La3+ when electrospraying proteins out of non-denaturing solutions. Here, we conducted mass spectrometry and ion mobility spectrometry experiments, in combination with molecular dynamics (MD) simulations, to uncover the mechanistic basis of this charge enhancement. MD simulations of aqueous ESI droplets reproduced the experimental observation that La3+ boosts protein charge states relative to monovalent metals (e.g., Na+). The simulations showed that gaseous proteins were released by solvent evaporation to dryness, consistent with the charged residue model. Metal ion ejection kept the shrinking droplets close to the Rayleigh limit until ∼99% of the solvent had left. For droplets charged with Na+, metal adduction during the final stage of solvent evaporation produced low protein charge states. Droplets containing La3+ showed a very different behavior. The trivalent nature of La3+ favored adduction to the protein at a very early stage, when most of the solvent had not evaporated yet. This irreversible binding via multidentate contacts suppressed La3+ ejection from the vanishing droplets, such that the resulting gaseous proteins carried significantly more charge. Our results illustrate that MD simulations are suitable for uncovering intricate aspects of electrospray mechanisms, paving the way toward an atomistic understanding of mass spectrometry based analytical workflows.

La, Ce and Nd in the soil-plant system in a vegetation experiment with barley (Hordeum vulgare L.).

Rare earth elements (REEs) have received enormous attention in recent years. However, there are many gaps in the understanding of their behavior in the soil-plant system. The aim of this study is to investigate the behavior of three most common REEs (La, Ce, Nd) in the soil-plant system directly on soil samples using barley (Hordeum vulgare L.) in a vegetation experiment. We attribute the absence of significant changes in plant biomass and photosynthetic pigment content to the reduced availability of REEs in soil samples. The concentration of water-soluble forms of La, Ce and Nd didn't exceed 1 mg/kg, while the concentration of exchangeable forms varied and decreased in a row La > Ce > Nd. The transfer factor (TF) from soil to above-ground biomass was low for all three elements (<1). The stem-to-leaf TF increased with the increase in REEs concentration in soil. The concentration in plant material increased in the row Ce < Nd < La. REEs concentrations in barley leaves didn't exceed 1-3% of the corresponding element concentration in soil samples. REEs concentration in plant tissues is in close direct correlation with the REEs total concentration in soil, water-soluble and exchange forms. REEs concentration in barley leaves is 3-4 times higher than in the stems and for the group with extraneous concentration of 200 mg/kg for La, Ce and Nd was 6.20 ± 1.48, 2.10 ± 0.51, 6.90 ± 3.00 mg/kg, respectively. We show that there were no major changes in barley plants, but further study is needed of the relationship between the absorption of lanthanides by plants and the content of various forms of lanthanides in the soil.