Energy Storage Molecules Research Articles

Long-Cycling Ferrocene/MV Aqueous Organic Redox Flow Battery (AORFB)

Redox flow batteries (RFBs) are a viable technology to store renewable energy in the form of electricity that can be supplied to electricity grids. However, widespread implementation of traditional RFBs, such as vanadium and Zn-Br2 RFBs, is limited due to a number of challenges related to materials, including low abundance and high costs of redox-active metals, expensive separators, and corrosive and hazardous electrolytes. To address these challenges, we demonstrate an aqueous organic redox flow battery (AORFB), named FcNCl/MV AORFB,1 featuring a high theoretical energy density, 45.5 Wh/L, the highest value known for AORFBs. The battery is built from earth abundant elements (C, H, N, and Fe), specifically consisting of a newly designed organic catholyte based on a highly water soluble ferrocene compound, (ferrocenylmethyl)trimethylammonium chloride(FcNCl), a methyl viologen anolyte which was studied in our previous work,2 non-flammableand non-corrosive NaCl supporting electrolyte, and low cost anion exchange membrane. This is the first application of a water-soluble ferrocene compound in aqueous RFBs. The batteries exhibit extraordinary electrochemical performances, 700 cycles with 99.99% capacity retention per cylce and 65% energy efficiency at 60 mA/cm2, and delivered power density up to 125 mW/cm2. The presented AORFB technology underlines great promise of soluble redox-active organic molecules for green energy storage. Reference 1. Hu, B.; DeBruler, C.; Rhodes, Z.; Liu, T. L., J. Am. Chem. Soc., 2017, 139, 1207. 2. Liu, T. B.; Wei, X. L.; Nie, Z. M.; Sprenkle, V.; Wang, W., Adv. Energy. Mater., 2016, 6, 1501449.

Transcriptome Analyses Shed New Insights into Primary Metabolism and Regulation of Blumeria graminis f. sp. tritici during Conidiation.

Conidia of the obligate biotrophic fungal pathogen Blumeria graminis f. sp. tritici (Bgt) play a vital role in its survival and rapid dispersal. However, little is known about the genetic basis for its asexual reproduction. To uncover the primary metabolic and regulatory events during conidiation, we sequenced the transcriptome of Bgt epiphytic structures at 3 (vegetative hyphae growth), 4 (foot cells initiation), and 5 (conidiophore erection) days post-inoculation (dpi). RNA-seq analyses identified 556 and 404 (combined 685) differentially expressed genes (DEGs) at 4 and 5 dpi compared with their expression levels at 3 dpi, respectively. We found that several genes involved in the conversion from a variety of sugars to glucose, glycolysis, the tricarboxylic acid cycle (TAC), the electron transport chain (ETC), and unsaturated fatty acid oxidation were activated during conidiation, suggesting that more energy supply is required during this process. Moreover, we found that glucose was converted into glycogen, which was accumulated in developing conidiophores, indicating that it could be the primary energy storage molecule in Bgt conidia. Clustering for the expression profiles of 91 regulatory genes showed that calcium (Ca2+), H2O2, and phosphoinositide (PIP) signaling were involved in Bgt conidiation. Furthermore, a strong accumulation of H2O2 in developing conidiophores was detected. Application of EGTA, a Ca2+ chelator, and trifluoperazine dihydrochloride (TFP), a calmodulin (CaM) antagonist, markedly suppressed the generation of H2O2, affected foot cell and conidiophore development and reduced conidia production significantly. These results suggest that Ca2+ and H2O2 signaling play important roles in conidiogenesis and a crosslink between them is present. In addition to some conidiation-related orthologs known in other fungi, such as the velvet complex components, we identified several other novel B. graminis-specific genes that have not been previously found to be implicated in fungal conidiation, reflecting a unique molecular mechanism underlying asexual development of cereal powdery mildews.

Electrochemical reduction of Bicarbonate to Formate with Silver Nanoparticles and Silver Nanoclusters supported on Multiwalled Carbon Nanotubes

In this work, we report heterogeneous catalysis of bicarbonate reduction to formate (FA) using silver nanoparticles (Ag NP) and silver nanoclusters (Ag NC) supported on multi-wall carbon nanotubes (MWCNT). FA detection was performed by substrate generation/tip collection (SG/TC) mode of scanning electrochemical microscopy (SECM) using Pt UME in 100mM HCO3− at pH 8. The Ag NP and Ag NC showed high carbonate reduction current, and similar activity as massive gold electrode targets them as alternative catalysts for FA production. Prior to bicarbonate reduction, the electrochemical activity of Ag NP and Ag NC was evaluated using carbon fiber ultra microelectrodes (UME), these carbon UME were fabricated and characterized for use in SCEM mapping; carbon UME provided an excellent feedback response and are dispensable electrodes with renewable surfaces. Also, a carbon UME enables the fabrication of an enzymatic sensor which was designed for NAD+ (Nicotine amide dinucleotide) dependent formate dehydrogenase immobilization. The enzymatic reaction coupled with the redox mediator 2,2V-Azino- bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) allowed a sensitive FA detection. The production of FA on silver particles and the FA detection methods presented in this work will be the target of further investigation for energy storage molecules.

Label-Free Discrimination of Rhizobial Bacteroids and Mutants by Single-Cell Raman Microspectroscopy.

Symbiotic rhizobia in legumes account for a large portion of nitrogen fixation in the biosphere. Nitrogen fixation is an energy-demanding process requiring tight control of metabolism and redox state. It is of great interest to understand the bacteroid differentiation process and the roles of energy storage molecules, such as glycogen and polyhydroxybutyrate (PHB), in maintaining the Rhizobium-legume symbioses. Traditional biochemical assays for checking phenotypic changes of mutants require a large volume of starting materials, which is difficult for unculturable, terminally differentiated bacteroids. Here we present a label-free technique that allows the identification and characterization of phenotypic changes of bacteria at the single-cell level. This work demonstrates the application of single-cell Raman spectra (SCRS) to differentiate Rhizobium leguminosarum bv. viciae wild-type and mutants under different conditions. We found symbiotically differentiated bacteroids and free-living bacteria differed primarily at a Raman biomarker, cytochrome c, corresponding to a bacteroid-specific terminal oxidase. We demonstrated that, for the first time, SCRS were able to link phenotypic changes and specific genetic mutants, in this case, single and double mutations in synthesis of carbon storage molecules glycogen and polyhydroxybutyrate (PHB). By analyzing SCRS of these mutants, it provides insights into metabolite production and carbon regulatory network of rhizobia.

A self-glycerophospholipid suppresses immunity and inflammation via recruitment of Ly6C+ myeloid cells

Abstract Membrane lipids function as essential components of biological membranes, as signaling molecules, and as energy storage molecules. Phosphatidic acid is a vital membrane lipid that serves as a precursor for the synthesis of all acylglycerol lipids in the cell. Phosphatidic acid participates in a wide range of cellular processes, including cytoskeletal organization, secretion, endocytosis, and cell proliferation. Here, we examined the effect of phosphatidic acid on myeloid cells and its ability to modulate tumor immunity and inflammatory disease. We found that in vivo administration of phosphatidic acid protected against immune mediated liver inflammation induced by concanavalin A, but worsened tumor spread in the B16F10 melanoma lung metastasis model. Phosphatidic acid reduced pro-inflammatory cytokines but increased anti-inflammatory cytokine interleukin-10 in the liver. Phosphatidic acid did so by inducing the mobilization and migration from the bone marrow to peripheral organs of Ly6C+ myeloid cells that upon adoptive transfer protected against autoimmune liver inflammation. Our novel observations indicating immune suppressive functions of phosphatidic acid may have wide implications for a variety of conditions with altered lipid metabolism and inflammation such as atherosclerosis and autoimmune disease and conditions with local or systemic alterations in phosphatidic acid such as osteoarthritis and Alzheimer’s disease.

Inspired by lipids: the Morton Lecture Award Presentation.

Lipids are key molecules for membranes, energy storage and signalling. I have been privileged to have worked in such a diverse field and in organisms from microbes to humans. Here I will describe some of those contrasting areas which range from environmental impacts to food production and on to human health. It has been a fascinating journey which still continues to excite me.

Caloric Restriction and Rapamycin Differentially Alter Energy Metabolism in Yeast.

Rapamycin (RM), a drug that inhibits the mechanistic target of rapamycin (mTOR) pathway and responds to nutrient availability, seemingly mimics the effects of caloric restriction (CR) on healthy life span. However, the extent of the mechanistic overlap between RM and CR remains incompletely understood. Here, we compared the impact of CR and RM on cellular metabolic status. Both regimens maintained intracellular ATP through the chronological aging process and showed enhanced mitochondrial capacity. Comparative transcriptome analysis showed that CR had a stronger impact on global gene expression than RM. We observed a like impact on the metabolome and identified distinct metabolites affected by CR and RM. CR severely reduced the level of energy storage molecules including glycogen and lipid droplets, whereas RM did not. RM boosted the production of enzymes responsible for the breakdown of glycogen and lipid droplets. Collectively, these results provide insights into the distinct energy metabolism mechanisms induced by CR and RM, suggesting that these two anti-aging regimens might extend life span through distinctive pathways.

A DFT Study of Multimode Switching in a Combined DHA/VHF-DTE/DHB System for Use in Solar Heat Batteries

Development of photochromic molecules for solar energy storage has two major challenges: (i) to store a sufficient amount of energy in the metastable isomer and (ii) to control the energy-releasing step, i.e., setting it on hold until the energy is needed. Combining the dihydroazulene/vinylheptafulvene (DHA/VHF) photo-/thermoswitch with the dithienylethene/dihydrothienobenzothiophene (DTE/DHB) photoswitch could potentially meet these challenges. The combined multimode switch is studied by density functional theory in order to predict its energy storage properties and spectral behavior in various solvents before discussing its suitability for use in solar heat batteries. An energy storage capacity of 0.17 MJ/kg is calculated which corresponds to a specific energy of 46 Wh/kg—slightly larger than that of a common lead–acid car battery (∼40 Wh/kg) but still only one-fourth of lithium-ion batteries (100–250 Wh/kg). The usual trend for 1,8a-dihydroazulene-1,1-dicarbonitrile and its derivatives is for their ene...

Stoichiometric Responses to an Agricultural Pesticide Are Modified by Predator Cues.

Current ecological risk assessment of pesticides fails to protect aquatic ecosystem health. To get better insight in how pesticides may affect aquatic ecosystems, we tested how sublethal pesticide concentrations modify body stoichiometry. Moreover, as interactions with natural stressors may cause underestimates of the impact of pesticides, we also tested whether this pathway depended on the presence of predator cues. Therefore, we exposed damselfly larvae to chlorpyrifos and cues from predatory dragonflies and focused on body stoichiometry and associated explanatory variables (growth rate, RNA:DNA, and energy storage molecules). The way the predator cues modulated the pesticide effects strongly differed between endpoints. Exposure to chlorpyrifos affected the key body stoichiometric ratios: chlorpyrifos consistently increased N:P, while its effects on C:N (decrease with predator cues) and C:P (increase without predator cues) strongly depended upon the presence of the natural stressor. These stoichiometric responses could be explained by associated changes in growth, RNA:DNA, and in C-rich fat and sugars and N-rich proteins. The observed changes in body stoichiometry may affect the damselflies' food quality and have the potential to cascade through the food web and shape nutrient cycling.

Morphological and genetic responses of lactobacillus plantarum FQR to nitrite and its practical applications

AbstractIn this article, the growth, morphological, and genetic responses of Lactobacillus plantarum FQR to nitrite were investigated. The growth and degrading ability of the strain to nitrite was delayed; slight changes were also observed on the cell surface. FQR exposed to 0.120% nitrite exhibited rough surfaces with folds, as shown by scanning electron microscopy. Transmission electron microscopy presented numerous white granules in the FQR incubated without nitrite, compared with FQR exposed to 0.045% and 0.120% nitrite. These granules are common energy storage molecules, which decrease with increasing nitrite concentration. In addition, nitrite reductase (nir) gene and membrane‐related genes were activated in varying degrees. A similar trend in relative gene expression indicated that the expression levels of membrane‐related genes (with the exception of lp_1403) in FQR increased significantly (p < .05) in the presence of 0.120% nitrite compared with 0.045% nitrite. However, a marked difference was shown for the nir gene in FQR; the nir gene exhibited a relatively low level of expression when exposed to 0.120% nitrite concentration. In summary, the cell morphology and genetic level of L. plantarum FQR were changed in varying degrees after treatment with different nitrite concentrations.Practical ApplicationsNitrite is an important food additive and nitrite pollution issues of fermented food have become an increasing concern given its potential hazards. L. plantarum has the function of degrading nitrite. However, the detailed mechanisms and pathways involved in the regulation of nitrite in L. plantarum were still unclear. In this article, the growth, morphological, and genetic responses of L. plantarum to nitrite were investigated. It serves as an important reference for future studies of the mechanism of signal transduction in L. plantarum and the mechanism of stress response, and to determine the possible regulating targets. In practice, it can serve as a reference for genetic engineering improvement of L. plantarum used in the fermented food industry reducing nitrite residue.

Direct Characterization of the Maize Starch Synthase IIa Product Shows Maltodextrin Elongation Occurs at the Non-reducing End

A comprehensive description of starch biosynthesis and granule assembly remains undefined despite the central nature of starch as an energy storage molecule in plants and as a fundamental calorie source for many animals. Multiple theories regarding the starch synthase (SS)-catalyzed assembly of (α1-4)-linked d-glucose molecules into maltodextrins generally agree that elongation occurs at the non-reducing terminus based on the degradation of radiolabeled maltodextrins, although recent reports challenge this hypothesis. Surprisingly, a direct analysis of the SS catalytic product has not been reported, to our knowledge. We expressed and characterized recombinant Zea mays SSIIa and prepared pure ADP-[13CU]glucose in a one-pot enzymatic synthesis to address the polarity of maltodextrin chain elongation. We synthesized maltoheptaose (degree of polymerization 7) using ADP-[13CU]glucose, maltohexaose (degree of polymerization 6), and SSIIa. Product analysis by ESI-MS revealed that the [13CU]glucose unit was added to the non-reducing end of the growing chain, and SSIIa demonstrated a >7,850-fold preference for addition to the non-reducing end versus the reducing end. Independent analysis of [13CU]glucose added to maltohexaose by SSIIa using solution NMR spectroscopy confirmed the polarity of maltodextrin chain elongation.

Photosynthesis.

Photosynthesis sustains virtually all life on planet Earth providing the oxygen we breathe and the food we eat; it forms the basis of global food chains and meets the majority of humankind's current energy needs through fossilized photosynthetic fuels. The process of photosynthesis in plants is based on two reactions that are carried out by separate parts of the chloroplast. The light reactions occur in the chloroplast thylakoid membrane and involve the splitting of water into oxygen, protons and electrons. The protons and electrons are then transferred through the thylakoid membrane to create the energy storage molecules adenosine triphosphate (ATP) and nicotinomide–adenine dinucleotide phosphate (NADPH). The ATP and NADPH are then utilized by the enzymes of the Calvin–Benson cycle (the dark reactions), which converts CO2 into carbohydrate in the chloroplast stroma. The basic principles of solar energy capture, energy, electron and proton transfer and the biochemical basis of carbon fixation are explained and their significance is discussed.

Cobalt Phosphide Based Nanostructures as Bifunctional Electrocatalysts for Low Temperature Alkaline Water Splitting

Hydrogen is regarded as a valuable high energy density, zero-emission fuel for the future, with the potential to reduce or eliminate fossil fuels. H2 also has potential as an energy carrier or storage molecule: i.e. being generated, stored, and consumed to bridge the gap of high and low production cycles of renewable energy sources, such as solar cells and wind turbines. Because molecular hydrogen is not naturally available, the complications of generation, storage and transportation must be addressed. On Earth, hydrogen (H) mainly occurs in combination with oxygen, i.e. in water. One possible technology option for clean H2 generation is low temperature water electrolysis, with the two half-reactions being the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). These reactions, particularly the OER, are mechanistically complex and dependent on the surface energy of multiple intermediate species, leading to high overpotentials and low efficiency. Precious metal-based catalyst materials are ultimately not viable, due to rarity and cost, and typically provide high catalytic activity for the OER or HER, but not both. More effective catalysts with the ability to catalyze both the OER and HER (i.e. OER/HER bi-functional behavior) could improve current electrolyzers and enable future technologies. Thus, there is a desire to design electrocatalysts based on earth- abundant, low-cost materials for overall water splitting. In this talk we will present on the synthesis and electrochemical characterization cobalt phosphide-based materials. CoP-based electrocatalysts in both thin film and nanoparticle form have been prepared from their respective Co3O4 spinel precursors using phosphine gas, generated in situ from the thermal decomposition of sodium hypophosphite. These electrocatalysts were found to have performance comparable to that of the commercial precious metal benchmarks when examined in alkaline electrolyte. For example, ΔE(OER–HER) values were calculated by adding the overpotentials at which j geo = 10 mA cm-2 and j geo = -10 mA cm-2were attained for the OER and HER, respectively, to the thermodynamic OER–HER potential difference of 1.23 V. Values of ΔE(OER–HER) = 1.77 V for cobalt phosphide catalysts are within 70 mV of the idealized water electrolysis with 20% Ir/C (anode):20% Pt/C (cathode) where ΔE(OER–HER) = 1.70 V. Various aspects of this work will be presented. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Trehalase plays a role in macrophage colonization and virulence of Burkholderia pseudomallei in insect and mammalian hosts

ABSTRACTTrehalose is a disaccharide formed from two glucose molecules. This sugar molecule can be isolated from a range of organisms including bacteria, fungi, plants and invertebrates. Trehalose has a variety of functions including a role as an energy storage molecule, a structural component of glycolipids and plays a role in the virulence of some microorganisms. There are many metabolic pathways that control the biosynthesis and degradation of trehalose in different organisms. The enzyme trehalase forms part of a pathway that converts trehalose into glucose. In this study we set out to investigate whether trehalase plays a role in both stress adaptation and virulence of Burkholderia pseudomallei. We show that a trehalase deletion mutant (treA) had increased tolerance to thermal stress and produced less biofilm than the wild type B. pseudomallei K96243 strain. We also show that the ΔtreA mutant has reduced ability to survive in macrophages and that it is attenuated in both Galleria mellonella (wax moth larvae) and a mouse infection model. This is the first report that trehalase is important for bacterial virulence.

Energy storage and fecundity explain deviations from ecological stoichiometry predictions under global warming and size-selective predation.

A key challenge for ecologists is to predict how single and joint effects of global warming and predation risk translate from the individual level up to ecosystem functions. Recently, stoichiometric theory linked these levels through changes in body stoichiometry, predicting that both higher temperatures and predation risk induce shifts in energy storage (increases in C-rich carbohydrates and reductions in N-rich proteins) and body stoichiometry (increases in C:N and C:P). This promising theory, however, is rarely tested and assumes that prey will divert energy away from reproduction under predation risk, while under size-selective predation, prey instead increase fecundity. We exposed the water flea Daphnia magna to 4°C warming and fish predation risk to test whether C-rich carbohydrates increase and N-rich proteins decrease, and as a result, C:N and C:P increase under warming and predation risk. Unexpectedly, warming decreased body C:N, which was driven by reductions in C-rich fat and sugar contents while the protein content did not change. This reflected a trade-off where the accelerated intrinsic growth rate under warming occurred at the cost of a reduced energy storage. Warming reduced C:N less and only increased C:P and N:P in the fish-period Daphnia. These evolved stoichiometric responses to warming were largely driven by stronger warming-induced reductions in P than in C and N and could be explained by the better ability to deal with warming in the fish-period Daphnia. In contrast to theory predictions, body C:N decreased under predation risk due to a strong increase in the N-rich protein content that offsets the increase in C-rich fat content. The higher investment in fecundity (more N-rich eggs) under predation risk contributed to this stronger increase in protein content. Similarly, the lower body C:N of pre-fish Daphnia also matched their higher fecundity. Warming and predation risk independently shaped body stoichiometry, largely by changing levels of energy storage molecules. Our results highlight that two widespread patterns, the trade-off between rapid development and energy storage and the increased investment in reproduction under size-selective predation, cause predictable deviations from current ecological stoichiometry theory.

Aerospace Applications of Conductive Polymers

Historically, the aerospace industry has driven major developments in polymer and material science. Technology has evolved from wood and coated fabric to metals to advanced polymer composite systems in response to demands of both the commercial and defense aerospace industries. Future systems will require event more advanced technologies such as those afforded by electroactive and conductive polymers (EAPs). The unique properties of these materials provide the ability to construct intelligent systems which produce a defined, predictable response to an input. For example, as a corrosion protection coating, an EAP would sense corrosion at the molecular level and release a corrosion inhibitor before major damage could occur. A self-detoxifying system would sense a toxin and respond by releasing bactericide to kill it. As depicted below, material advancements being sought for future aerospace systems include: Controllable optical absorption and emission across a wide spectral rangeTunable conductivity from 10-5 to >10,0000 S/cm for antistatic and shieldingControlled, on demand release of active molecules for self-repair, detoxification and corrosion protectionHigh power energy storage and capture This presentation will explore some of the issues involved with developing and transitioning EAP technology into current and future aerospace products.

The Lipid-Modifying Enzyme SMPDL3B Negatively Regulates Innate Immunity.

SummaryLipid metabolism and receptor-mediated signaling are highly intertwined processes that cooperate to fulfill cellular functions and safeguard cellular homeostasis. Activation of Toll-like receptors (TLRs) leads to a complex cellular response, orchestrating a diverse range of inflammatory events that need to be tightly controlled. Here, we identified the GPI-anchored Sphingomyelin Phosphodiesterase, Acid-Like 3B (SMPDL3B) in a mass spectrometry screening campaign for membrane proteins co-purifying with TLRs. Deficiency of Smpdl3b in macrophages enhanced responsiveness to TLR stimulation and profoundly changed the cellular lipid composition and membrane fluidity. Increased cellular responses could be reverted by re-introducing affected ceramides, functionally linking membrane lipid composition and innate immune signaling. Finally, Smpdl3b-deficient mice displayed an intensified inflammatory response in TLR-dependent peritonitis models, establishing its negative regulatory role in vivo. Taken together, our results identify the membrane-modulating enzyme SMPDL3B as a negative regulator of TLR signaling that functions at the interface of membrane biology and innate immunity.

Decolorization of Distillery Spent Wash Using Biopolymer Synthesized by Pseudomonas aeruginosa Isolated from Tannery Effluent.

A bacterial strain was isolated from tannery effluent which can tolerate high concentrations of potassium dichromate up to 1000 ppm. The isolated microorganism was identified as Pseudomonas aeruginosa by performing biochemical tests and molecular characterization. In the presence of excess of carbohydrate source, which is a physiological stress, this strain produces Polyhydroxybutyrate (PHB). This intracellular polymer, which is synthesized, is primarily a product of carbon assimilation and is employed by microorganisms as an energy storage molecule to be metabolized when other common energy sources are limitedly available. Efforts were taken to check whether the PHB has any positive effect on spent wash decolorization. When a combination of PHB and the isolated bacterial culture was added to spent wash, a maximum color removal of 92.77% was found which was comparatively higher than the color removed when the spent wash was treated individually with the PHB and Pseudomonas aeruginosa. PHB behaved as a support material for the bacteria to bind to it and thus develops biofilm, which is one of the natural physiological growth forms of microorganisms. The bacterial growth in the biofilm and the polymer together acted in synergy, adsorbing and coagulating the pollutants in the form of color pigments.

Silver dopants for targeted and untargeted direct analysis of unsaturated lipids via infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI).

Unsaturated lipids play a crucial role in cellular processes as signaling factors, membrane building blocks or energy storage molecules. However, adequate mass spectrometry imaging of this diverse group of molecules remains challenging. In this study we implemented silver cationization for direct analysis by infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) to enhance the ion abundances for olefinic lipids and facilitate peak assignment. Trace amounts of silver nitrate were doped into the electrospray solvent of an IR-MALDESI imaging source coupled to an Orbitrap mass analyzer. Calcifediol was examined as a model compound to demonstrate the effect of silver dopants on sensitivity and assay robustness. Dried human serum spots were subsequently analyzed to compare Ag-doped solvents with previously described solvent compositions. Mass differences as well as ion abundance ratio filters were employed to interpret results based on the characteristic isotopic pattern of silver. Olefinic lipids were readily observed as silver adducts in IR-MALDESI analyses. Silver cationization decreased the limit of detection for calcifediol by at least one order of magnitude and was not affected in complex biological matrices. The ion abundance ratio and mass difference of [M + (107) Ag(+)](+) and [M + (109) Ag(+)](+) were successfully applied to facilitate the spectral assignment of silver adducts. Overall, silver cationization increased the analyte coverage in human serum by 43% compared with a standard IR-MALDESI approach. Silver cationization has been shown to enhance IR-MALDESI sensitivity and selectivity for unsaturated lipids, even when applied to complex samples. Increased compound coverage, enhanced robustness as well as the developed tools for peak assignment and mapping of isotopic patterns will clearly benefit future mass spectrometry imaging studies.

Dictyostelium discoideum Dgat2 Can Substitute for the Essential Function of Dgat1 in Triglyceride Production but Not in Ether Lipid Synthesis

Triacylglycerol (TAG), the common energy storage molecule, is formed from diacylglycerol and a coenzyme A-activated fatty acid by the action of an acyl coenzyme A:diacylglycerol acyltransferase (DGAT). In order to conduct this step, most organisms rely on more than one enzyme. The two main candidates in Dictyostelium discoideum are Dgat1 and Dgat2. We show, by creating single and double knockout mutants, that the endoplasmic reticulum (ER)-localized Dgat1 enzyme provides the predominant activity, whereas the lipid droplet constituent Dgat2 contributes less activity. This situation may be opposite from what is seen in mammalian cells. Dictyostelium Dgat2 is specialized for the synthesis of TAG, as is the mammalian enzyme. In contrast, mammalian DGAT1 is more promiscuous regarding its substrates, producing diacylglycerol, retinyl esters, and waxes in addition to TAG. The Dictyostelium Dgat1, however, produces TAG, wax esters, and, most interestingly, also neutral ether lipids, which represent a significant constituent of lipid droplets. Ether lipids had also been found in mammalian lipid droplets, but the role of DGAT1 in their synthesis was unknown. The ability to form TAG through either Dgat1 or Dgat2 activity is essential for Dictyostelium to grow on bacteria, its natural food substrate.