Author Correction: Evidence for a Fe3+-rich pyrolitic lower mantle from (Al,Fe)-bearing bridgmanite elasticity data.

In Extended Data Table 1 of this Letter, some of the elastic constants were reported incorrectly. This occurred as a result of an error in the script used to generate the numbers. The values of the elastic constants at room pressure cited in the manuscript on page 544 were derived using the same erroneous script, and the correct values and 1σ-uncertainties in the last given digit are C11 = 461.3(17) GPa instead of 462.7(17) GPa; C22 = 509.7(26) GPa instead of 504.9(26) GPa; C33 = 425.7(5) GPa instead of 426.6(5) GPa; C44 = 188.8(6) GPa instead of 188.4(6) GPa; C55 = 166.5(4) GPa instead of 166.6(4) GPa; C66 = 127.2(17) GPa instead of 129.7(17) GPa; C12 = 141.7(14) GPa instead of 140.2(14) GPa; C13 = 130.0(11) GPa instead of 132.2(11) GPa; and C23 = 161.0(12) GPa instead of 159.3(12) GPa. These errors do not affect any of the conclusions and we apologize for any confusion this may have caused. Extended Data Table 1 and the room-pressure values in the text have been corrected online. The Supplementary Information of this Author Correction contains the original, incorrect Extended Data Table 1, for transparency.

Evidence for a Fe3+-rich pyrolitic lower mantle from (Al,Fe)-bearing bridgmanite elasticity data.

The chemical composition of Earth's lower mantle can be constrained by combining seismological observations with mineral physics elasticity measurements. However, the lack of laboratory data for Earth's most abundant mineral, (Mg,Fe,Al)(Al,Fe,Si)O3 bridgmanite (also known as silicate perovskite), has hampered any conclusive result. Here we report single-crystal elasticity data on (Al,Fe)-bearing bridgmanite (Mg0.9Fe0.1Si0.9Al0.1)O3 measured using high-pressure Brillouin spectroscopy and X-ray diffraction. Our measurements show that the elastic behaviour of (Al,Fe)-bearing bridgmanite is markedly different from the behaviour of the MgSiO3 endmember. We use our data to model seismic wave velocities in the top portion of the lower mantle, assuming a pyrolitic mantle composition and accounting for depth-dependent changes in iron partitioning between bridgmanite and ferropericlase. We find excellent agreement between our mineral physics predictions and the seismic Preliminary Reference Earth Model down to at least 1,200 kilometres depth, indicating chemical homogeneity of the upper and shallow lower mantle. A high Fe3+/Fe2+ ratio of about two in shallow-lower-mantle bridgmanite is required to match seismic data, implying the presence of metallic iron in an isochemical mantle. Our calculated velocities are in increasingly poor agreement with those of the lower mantle at depths greater than 1,200 kilometres, indicating either a change in bridgmanite cation ordering or a decrease in the ferric iron content of the lower mantle.

The development of internal pressure standards for in-house elastic wave velocity measurements in multi-anvil presses.

Ultrasonic systems are powerful tools to determine elastic wave velocities of minerals and materials at high pressure and temperature and have been extensively developed in recent decades. However, accurate measurement of sample length is required to convert travel times into wave velocities, limiting their use to synchrotron facilities or room temperature experiments in laboratories. We have made use of a close collaboration between the Bayerisches Geoinstiut and the P61B end-station beamline (PETRA III - DESY) to install ultrasonic systems and develop a novel dual travel time method for in situ pressure determination without the need for synchrotron radiation. Our method relies on the travel times of elastic waves through a reference material; it requires a thermocouple and is non-intrusive, with the reference material replacing the backing plate of the high-pressure assembly. Pressures obtained from this dual travel time method show excellent agreement with those obtained from x-ray diffraction using synchrotron radiation on standard materials. Our novel method enables in situ pressure determination at varying temperatures during in-house ultrasonic interferometry experiments. This allows us not only to determine the elastic behavior of minerals and materials but also to investigate phase diagrams, solidus, or liquidus conditions at varying pressures and temperatures during in-house experiments. During the installation of the pulse-echo ultrasonic system, we identified critical parameters for obtaining reliable data. While these requirements are well-known to experts, this study presents a comprehensive review of the different characteristics of ultrasonic systems, providing user-friendly guidelines for new users installing and operating such systems in high-pressure and high-temperature conditions.

Combining FIB milling and conventional Argon ion milling techniques to prepare high-quality site-specific TEM samples for quantitative EELS analysis of oxygen in molten iron.

This paper reports a procedure to combine the focused ion beam micro-sampling method with conventional Ar-milling to prepare high-quality site-specific transmission electron microscopy cross-section samples. The advantage is to enable chemical and structural evaluations of oxygen dissolved in a molten iron sample to be made after quenching and recovery from high-pressure experiments in a laser-heated diamond anvil cell. The evaluations were performed by using electron energy-loss spectroscopy and high-resolution transmission electron microscopy. The high signal to noise ratios of electron energy-loss spectroscopy core-loss spectra from the transmission electron microscopy thin foil, re-thinned down to 40 nm in thickness by conventional Argon ion milling, provided us with oxygen quantitative analyses of the quenched molten iron phase. In addition, we could obtain lattice-fringe images using high-resolution transmission electron microscopy. The electron energy-loss spectroscopy analysis of oxygen in Fe(0.94)O has been carried out with a relative accuracy of 2%, using an analytical procedure proposed for foils thinner than 80 nm. Oxygen K-edge energy-loss near-edge structure also allows us to identify the specific phase that results from quenching and its electronic structure by the technique of fingerprinting of the spectrum with reference spectra in the Fe-O system.

Synthesis of hexagonal Ni(3)N using high pressures and temperatures.

The only known bulk ambient pressure nickel nitride phase is hexagonal Ni(3)N (space group P6(3)22). Multianvil synthesis experiments at 20 GPa and 2000 K using nickel (Ni) and sodium azide (NaN(3)) starting materials, and ex situ analysis using transmission electron microscopy and scanning electron microscopy measurements show that this phase can be recovered at ambient pressure (space group P6(3)22, a = 4.62 Å, c = 4.30 Å, Z = 2). Formation of this phase is correlated with the repulsive interactions between closely spaced nitrogen ions and with the extent of thermal stability of nickel nitride at ambient and at high densities. These two factors are also important in relating the high temperature and pressure behaviour of nickel nitride to those of several other interstitial nitrides recovered from similar pressures after heating. Further, we report formation of a sodium rhenium nitride phase by reaction of the azide with the rhenium capsule in which the reactants were contained.

Inhibition of yeast (1,3)-beta-glucan synthase by phospholipase A2 and its reaction products.

Fungal (1,3)-beta-glucan synthases are sensitive to a wide range of lipophilic inhibitors and it has been proposed that enzyme activity is highly sensitive to perturbations of the membrane environment. Yeast membranes were exposed to phospholipases and various lipophilic compounds, and the resultant effects on glucan synthase activity were ascertained. Glucan synthase from Saccharomyces cerevisiae was rapidly inactivated by phospholipase A2 (PLA2), and to a lesser extent by phospholipase C. Inactivation was time and dose-dependent and was protected against by EDTA and fatty-acid binding proteins (bovine and human serum albumins). Albumins also partially protected against inhibition by papulacandin B. PLA2 reaction products were structurally characterized and it was shown that fatty acids and lysophospholipids were the inhibitory moieties, with no novel inhibitory compounds apparent. Glucan synthase was inhibited by a range of fatty acids, monoglycerides and lysophospholipids. Inhibition by fatty acids was non-competitive, and progressive binding of [14C]oleic acid correlated with activity loss. Fluorescence anisotropy studies using diphenylhexatriene (DPH) confirm that fatty acids increase membrane fluidity. These results are consistent with proposals suggesting that glucan synthase inhibition is due in part to non-specific detergent-like disruption of the membrane environment, in addition to direct interactions of lipophilic inhibitors with specific target sites on the enzyme complex.

New antimitotic agents with activity in multi-drug-resistant cell lines and in vivo efficacy in murine tumor models.

During a screen for compounds that could inhibit cell proliferation, a series of new tubulin-binding compounds was identified with the discovery of oxadiazoline 1 (A-105972). This compound showed good cytotoxic activity against non-multi-drug-resistant and multi-drug-resistant cancer cell lines, but its utility in vivo was limited by a short half-life. Medicinal chemistry efforts led to the discovery of indolyloxazoline 22g (A-259745), which maintained all of the in vitro activity seen with oxadiazoline 1, but also demonstrated a better pharmacokinetic profile, and dose-dependent in vivo activity. Over a 28 day study, indolyloxazoline 22g increased the life span of tumor-implanted mice by up to a factor of 3 upon oral dosing. This compound, and others of its structural class, may prove to be useful in the development of new chemotherapeutic agents to treat human cancers.

The PMR analysis of non-conjugated alkenoic and alkynoic acids and esters.

The 220 MHz PMR spectra of 143 non-conjugated alkenoic and alkynoic acids and esters are correlated so as to provide a method for the structural analysis of such compounds in general. The spectral data are explained in terms of long-range deshielding of the double bonds, triple bonds, acid and ester groups in the molecules, and parameters are derived to quantify the influence of these groups on the chemical shifts of methyl and methylene protons up to six carbon atoms distant along an alkyl chain. It is shown that, by the application of these parameters, 220 MHz PMR spectroscopy can be used to determine both the stereochemistry and position of double bonds, and the position of triple bonds, in the majority of fatty acids and esters. The 2- to 9- and 13- to 17-cis- and trans-isomers of octadecenoic acid may be readily idenfited in this way, whilst for the octadecynoic acids all positional isomers may be characterized. Examples are also given of the structural analysis of several polyenoic compounds, including methyl cis-5, cis-8, cis-11, cis-14, cis-5, cis-8, cis-11, trans-14, and trans-5, cis-8, cis-11, cis-14-eicosatetraenoates, and methyl trans-5, cis-9, cis-12-octadecatrienoate.

PMR analysis of unsaturated triglycerides using shift reagents.

The addition of Pr(fod)3 i.e. tris(1,1,1,2,2,3,3-heptafluoro-,7-dimethyl 1-4,6-octanedionato) praseodymium, to trilinolein has been found to induce a difference in the chemical shifts of the absorptions from the acids on the alpha- and beta positions. At 220 MHz this was observed up to 18 carbon atoms along the chain. Decoupling of the alkenyl protons at 100 MHz enabled the absorptions from the skipped methylene groups to be used to determine the position of linoleate and linolenante chains in triglycerides.

A whole-cell Candida albicans assay for the detection of inhibitors towards fungal cell wall synthesis and assembly.

A whole-cell C. albicans screen was designed to identify novel inhibitors interacting with the synthesis, assembly and regulation of the fungal cell wall. C. albicans was grown in a paired broth assay in 96-well plates with natural product extracts or pure chemical compounds in the presence and absence of the osmotic stabilizer, sorbitol. Growth was visually examined over a 7-day period and scored into different growth categories. Positives from the sorbitol rescue were then examined under the microscope for morphological alterations and grouped into several morphological classes. Sorbitol protection and cell morphology were indicators of novel antifungal agents from natural product extracts and pure compounds.

Fusacandins A and B; novel antifungal antibiotics of the papulacandin class from Fusarium sambucinum. I. Identity of the producing organism, fermentation and biological activity.

The fuscandins, antifungal agents of the papulacandin class, are produced by a strain of Fusarium sambucinum. Fermentation yielded 60 mg/liter of fusacandin A and minor amounts of fusacandin B. As expected, the fusacandins inhibit (1,3)-beta-glucan synthesis. Fusacandin A is slightly less active than papulacandin B against Candida albicans and, like papulacandin, loses activity in the presence of serum.

Water-borne Bacillus licheniformis infection in mice.

A water-borne Bacillus licheniformis infection was associated with depressed haemoglobin content, white cell and platelet count. The epidemic was resolved by changing from tanked to mains water supply.

The redox state of the mantle during and just after core formation.

Siderophile elements are depleted in the Earth's mantle, relative to chondritic meteorites, as a result of equilibration with core-forming Fe-rich metal. Measurements of metal-silicate partition coefficients show that mantle depletions of slightly siderophile elements (e.g. Cr, V) must have occurred at more reducing conditions than those inferred from the current mantle FeO content. This implies that the oxidation state (i.e. FeO content) of the mantle increased with time as accretion proceeded. The oxygen fugacity of the present-day upper mantle is several orders of magnitude higher than the level imposed by equilibrium with core-forming Fe metal. This results from an increase in the Fe2O3 content of the mantle that probably occurred in the first 1Ga of the Earth's history. Here we explore fractionation mechanisms that could have caused mantle FeO and Fe2O3 contents to increase while the oxidation state of accreting material remained constant (homogeneous accretion). Using measured metal-silicate partition coefficients for O and Si, we have modelled core-mantle equilibration in a magma ocean that became progressively deeper as accretion proceeded. The model indicates that the mantle would have become gradually oxidized as a result of Si entering the core. However, the increase in mantle FeO content and oxygen fugacity is limited by the fact that O also partitions into the core at high temperatures, which lowers the FeO content of the mantle. (Mg,Fe)(Al,Si)O3 perovskite, the dominant lower mantle mineral, has a strong affinity for Fe2O3 even in the presence of metallic Fe. As the upper mantle would have been poor in Fe2O3 during core formation, FeO would have disproportionated to produce Fe2O3 (in perovskite) and Fe metal. Loss of some disproportionated Fe metal to the core would have enriched the remaining mantle in Fe2O3 and, if the entire mantle was then homogenized, the oxygen fugacity of the upper mantle would have been raised to its present-day level.

Interaction of sulfhydryl reactive reagents with components involved in (1,3)-beta-glucan synthesis from Candida albicans.

Glucan synthesis was sensitive to several sulfhydryl reacting compounds: mercurials, reversible disulfides, and an alkylating sulfhydryl reagent (IC50 3-45 microM). Thiol groups associated with glucan synthesis were hydrophilic in nature, since both hydrophilic and hydrophobic reagents were active. Glucan synthase complex consists of at least two components: a peripheral GTP-binding protein that can be solubilized with detergents (supernatant) and the catalytic membrane-bound component (pellet). A rapid separation technique was developed to study sulfhydryl interactions with the complex. The GTP-binding protein was solubilized with 0.6% 3-((3-cholamidopropyl)dimethylammonio)-1-propane sulfonate from isolated microsomes of Candida albicans cells grown at either 10 or 30 degrees C. The residual membranous fraction contained the core catalytic moiety of glucan synthase. Both fractions were devoid of glucan synthase activity until they were reconstituted by mixing the two fractions together. In reconstitution experiments, the pellet lost almost 50% activity when preincubated with 2.5 microM N-ethylmaleimide and combined with an untreated supernatant whereas only 10% activity was lost when the supernatant was treated with N-ethylmaleimide. The catalytic active site of glucan synthase was not protected with UDP-Glc when preincubated with 10 microM N-ethylmaleimide but the GTP-binding fraction was partially protected with GTP gamma S.

Characterization of (1,3)-beta-glucan synthase in Candida albicans: microsomal assay from the yeast or mycelial morphological forms and a permeabilized whole-cell assay.

A systematic evaluation of the in vitro (1,3)-beta-glucan synthase assay parameters was performed using microsomes prepared from Candida albicans from either yeast or mycelial phase cells. Enzyme activities of both yeast and mycelial phase microsomes depended on the presence of guanosine-5'-O-(3-thiophosphate) and either bovine serum albumin or a detergent [W-1 (polyoxyethylene ether detergent) or Brij-35 (polyoxyethylene ether, 23 lauryl ether)]. Brij-35 was included in standard assays as it was compatible with the permeabilized whole-cell assay. Microsomes derived from both the yeast and mycelial phases generally yielded similar glucan synthase activities under a range of different assay conditions. Brij-35 significantly stabilized the enzyme, yielding a half-life of 5.6 d at 4 degrees C, compared with 0.9 d without detergent. The addition of detergent during mechanical breakage of yeast cells dramatically improved glucan synthase stability and activity. Enzyme catalysis was linear for at least 75 min with 100 micrograms protein from microsomes of yeast cells grown to mid-exponential phase, with an apparent Km for UDP-glucose of 1.1 mM. The pH and temperature optima were 7.75 and 30 degrees C, respectively. Glucan synthase activity was highest in cells derived from early mid-exponential phase and declined to a basal level by stationary phase. A permeabilization-based in situ assay for glucan synthase was developed. Cells were permeabilized with 2% (v/v) solution of toluene/methanol (1:1) and assayed for glucan synthase activity using standard reaction mixtures. Reactions were linear for 30 min and were inhibited by known inhibitors of glucan synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of cilofungin as direct fluorescent probe for monitoring antifungal drug-membrane interaction.

Cilofungin is an antifungal cyclopeptide which inhibits cell wall (1,3)-beta-glucan biosynthesis in fungal organisms, and its action against Candida albicans (1,3)-beta-glucan synthase has been widely studied. Since glucan synthase inactivation is thought to partially result from perturbations of the membrane lipid environment, the interaction of cilofungin with fungal membranes and phosphatidylcholine membrane vesicles was studied. Cilofungin, which contains two independent aromatic groups, has an excitation maximum of 270 nm and an emission maximum of 317 nm in aqueous solution. Comparison of the fluorescence properties of cilofungin with those of the analogs pneumocandin B0, N-acetyl-tyrosinamide, and 4-hydroxybenzamide indicated that the emission of cilofungin largely derived from the p-octyloxybenzamide side chain. Microsomal membranes from Saccharomyces cerevisiae, C. albicans, and phosphatidylcholine membrane vesicles induced a blue shift in the cilofungin emission spectrum and increased the cilofungin steady-state emission anisotropy, providing direct evidence for a cilofungin-membrane interaction. Cilofungin interacted more strongly with membranes of C. albicans than with those of S. cerevisiae, correlating with previous findings that C. albicans is far more susceptible than S. cerevisiae to the action of cilofungin. These findings support the hypothesis that drug-induced inhibition of the (1,3)-beta-glucan synthesis results from the perturbation of the membrane environment and the interaction with the glucan synthase complex combined. The study demonstrated ways in which the fluorescence properties of drugs can be used to directly evaluate drug-membrane interactions and structure-activity relationships.

Rapid Enrichment of CHAPS-Solubilized UDP-Glucose: (1,3)-beta-Glucan (Callose) Synthase from Beta vulgaris L. by Product Entrapment : Entrapment Mechanisms and Polypeptide Characterization.

Rapid enrichment of CHAPS-solubilized UDP-glucose:(1,3)-beta-glucan (callose) synthase from storage tissue of red beet (Beta vulgaris L.) is obtained when the preparation is incubated with an enzyme assay mixture, then centrifuged and the enzyme released from the callose pellet with a buffer containing EDTA and CHAPS (20-fold purification relative to microsomes). When centrifuged at high speed (80,000g), the enzyme can also be pelleted in the absence of substrate (UDP-Glc) or synthesis of callose, due to nonspecific aggregation of proteins caused by excess cations and insufficient detergent in the assay buffer. True time-dependent and substrate-dependent product-entrapment of callose synthase is obtained by low-speed centrifugation (7,000-11,000g) of enzyme incubated in reaction mixtures containing low levels of cations (0.5 millimolar Mg(2+), 1 millimolar Ca(2+)) and sufficient detergent (0.02% digitonin, 0.12% CHAPS), together with cellobiose, buffer, and UDP-Glc. Entrapment conditions, therefore, are a compromise between preventing nonspecific precipitation of proteins and permitting sufficient enzyme activity for callose synthesis. Further enrichment of the enzyme released from the callose pellet was not obtained by rate-zonal glycerol gradient centrifugation, although its sedimentation rate was greatly enhanced by inclusion of divalent cations in the gradient. Preparations were markedly cleaner when product-entrapment was conducted on enzyme solubilized from plasma membranes isolated by aqueous two-phase partitioning rather than by gradient centrifugation. Product-entrapped preparations consistently contained polypeptides or groups of closely-migrating polypeptides at molecular masses of 92, 83, 70, 57, 43, 35, 31/29, and 27 kilodaltons. This polypeptide profile is in accordance with the findings of other callose synthase enrichment studies using a variety of tissue sources, and is consistent with the existence of a multi-subunit enzyme complex.