First-principle study of interfacial properties between γ-TiAl and TiC,VN

The adhesion, wettability, atomic bonding and electronic structure of γ-TiAl(110)/TiC(100) and γ-TiAl(110)/VN(100) interfaces were performed and investigated using first-principle calculations. Surface energy of γ-TiAl, TiC and VN with low crystal indices was calculated and compared, respectively. The three Al-terminated γ-TiAl(110)/ceramic(100) interface models were investigated to illustrate the interfacial bonding nature. The structure of Al atom placed on the top of the metalloid C and N atoms at the interface is the preferred interfacial structure with the larger work of adhesion. The electronic structure results show that the structure with metalloid site exists with the stronger polar covalent bonding between the interfacial Al and metalloid atom. The interfacial structure with metal site exhibits a mixture of the metallic features with some degree of covalent features. The simulation results are in agreement with the experimental results, in which the γ-TiAl/TiC interface exhibits the better wettability and stronger bonding than the γ-TiAl/VN interface.     

Resorcinolic lipids improve the properties of sphingomyelin–cholesterol liposomes

Alkylresorcinolic lipids isolated from cereal grains and their semi-synthetic myristoyl-sulphonyl derivatives (MSAR) were used to modify small long-circulating sphingomyelin–cholesterol liposomes. Those SM:Chol vesicles modified with 10–30 mol% resorcinolic lipids had stable size and low membrane permeability in vitro at 4 °C and 37 °C. Liposomes containing 30 mol% MSAR showed very fast solute release in the presence of human plasma at 37 °C, which was drastically diminished in heat-inactivated plasma. In vivo studies showed that unmodified SM:Chol liposomes and those modified with alkylresorcinols were eliminated from the circulation more slowly than liposomes with the highest concentration of MSAR in membrane and were located mostly in the liver and spleen.     

Stabilization of β-glucosidase by polyhydric alcohols

Thermal stability of β-glucosidase in Thermomonospora curvata lysed cell extracts, culture solids and lyophilized cells was increased 9–16-fold by polyhydric alcohols. Sorbitol, the most soluble of these alcohols, doubled the recovery of β-glucosidase during preliminary purification procedures.     

A study of the synthesis of γ-pantothenate by neurospora

Acetone-dried mycellium of wild-type Neurospora crassa Em5256A was able to synthesize γ-pantothenate from pantoyl lactone and γ-aminobutyric acid. Microbioassay with Lactobacillus arabinosus 17-5 was used to test for γ-pantothenate production. In some experiments δ-pantothenate was also produced from δ-amino-n-valeric acid and pantoyl lactone. Centrifuged enzyme extracts from wild-life-type Neuropora were also active in synthesizing pantothenate and its homolog from their precursors. The Neurospora pantothenicless mutant 5531A (pan 1A) was able to synthesize β-pantothenate, γ-pantothenate and δ-pantothenate in vitro from their precursors. Under the same conditions the Neurospora mutant pan-2A synthesized β-pantothenate, γ-pantothenate and δ-pantothenate in vitro and in vitro. However, the pantothenicless mutant pan-1A could not use γ-pantothenate for growth in the concentrations tested. The pan-2A strain could use γ-pantothenate acid, but it also grew well on pantoyl lactone. The synthesis of β-synthesis of β-pantothenate and γ-pantothenate requires both enzyme and co-enzyme to catalyze the coupling reaction from their precursors.     

A comparison of the interfacial interactions of the apoprotein from high density lipoprotein and β-casein with phospholipids

The conformations adopted by β-casein and the total apoprotein from serum high density lipoprotein when spread at the air-water interface are compared; the monolayer data are consistent with the apoprotein being α-helical and the β-casein being disordered with segments distributed in loops and trains. The penetration of these hydrophobic proteins into phosphatidylcholine monolayers in different physical states was investigated. More protein can penetrate into monolayers when they are in the liquid-expanded state; for penetration at constant total surface area the lateral compressibility of the lipid is an important factor. The charge and conformation of the polar group of the phospholipid does not have a major influence on the interaction. The mixed films of lipid and protein have a mosaic structure; probably the β-casein is in a compressed state whereas the apoprotein is extended as α-helices in the plane of the interface. The chain-length dependences of the interaction of the apoprotein with phosphatidylcholine monolayers and bilayers are different; when the apoprotein binds to bilayers of shorter-chain phosphatidylcholines it alters the shape of the lipid-water interface whereas with monolayers the interface remains planar throughout.     

Lipase-catalyzed interfacial polymerization of ω-pentadecalactone in aqueous biphasic medium: A mechanistic study

The synthetic activity of lipases in biphasic o/w systems was investigated with respect to their use in the synthesis of polyester chains via transesterification reactions. Lipase-catalyzed ring-opening polymerization (ROP) of pentadecalactone (ω-PDL) dispersed in water was used as a model reaction to understand the synthetic activity of lipases in biphasic o/w system. We conducted a systematic investigation of the influence of reaction conditions on the macromolecular characteristics of oligo(ω-PDL) encompassing chemical, thermophysical and colloidal properties of the reaction medium. A model was proposed assuming Michaelis–Menten interfacial kinetics followed by chain extension via lipase-catalyzed linear polycondensation. The solidification of oligo(ω-PDL) chains with a degree of polymerization of approximately three was identified as a major factor limiting the molecular weight of obtained oligomers to ∼870 g mol⁻¹, despite the fast reaction rate and complete conversion of ω-PDL. The addition of toluene into the dispersed phase at a volumetric ratio of 0.3–0.5 of toluene to ω-PDL allowed us to circumvent this problem and increase the molecular weight of obtained oligomers up to 1460 g mol⁻¹. The molecular weight of polymer product according to this model was thus inversely related to the weight ratio percentage of interfacial lipase PS to ω-PDL per droplet and correspondingly correlated with the activity of lipase. Taking into account all these parameters allowed increasing the molar mass of oligo(ω-PDL) from 870 g mol⁻¹ to 3507 g mol⁻¹.     

A method to determine tannin concentration by the measurement and quantification of protein — tannin interactions

Summary Protein determinations on protein-tannin complexes after protein isolation (gel filtration and trichloroacetic acid [TCA] precipitation) or phenolic extraction (polyvinyl pyrrolidone [PVP] and organic solvent precipitation) were unsuccessuful. Kjeldahl determinations of the amount of unprecipitated protein bovine serum albumin [BSA] showed a sigmoid relationship with increasing concentrations of tannins. A similar relationship was found for the reduced viscosity of BSA and plant protein, and the concentration of tannin. Non-linear regression and curve normalization allowed three variable (k₁, k₂ and T_1/2) to be defined for the quantification of the protein-tannin interaction/s. Such a treatment may be useful in studies of the role of tannins in plant-herbivore interactions.     

A determination of liquid–vapour interfacial properties for methanol using a linear-combination-based isotropic periodic sum

We performed molecular dynamics simulations of the methanol liquid–vapour interfacial systems for a wide temperature range of 200–350 K. The linear-combination-based isotropic periodic sum (LIPS) method was used for estimating Coulombic interactions of the systems. The temperature dependence of the liquid and vapour phase densities, surface thickness and surface tension using the LIPS method was almost equal to that of the Ewald sum method. The temperature dependence of the electrostatic potential profile using the LIPS method was very similar to that of the Ewald sum method. We conclude that the LIPS method provides a reasonable accuracy in determining the liquid–vapour interfacial properties of polar molecules for many temperature conditions.     

Production of nikkomycin by immobilized Streptomyces cells — Physiological properties

Summary The antibiotic nikkomycin can be produced by calcium alginate immobilized mycelium of Streptomyces tendae Tü 901 in batch and continuous culture.Scanning electron micrographs show the porous structure of the matrix and the distribution of the cells in the gel.Some physiological properties of free and immobilized mycelia were compared. Immobilization does not change the relative amounts of nikkomycin compounds in the culture broth. DNA and protein content were the same in free and immobilized cells. The specific activity of fructosediphosphate aldolase dropped during fermentation and was lower for entrapped than for free cells. The specific activity of mannitol dehydrogenase increased up to the end of the fermentation and was the same for free and immobilized mycelium.In continuous culture the relative amount of mannitol consumed decreased with increasing flow rate. When the medium was supplemented with amino acids mannitol consumption increased significantly.Dedicated to Prof. Dr. L. Acker on the occasion of his 70th birthday     

Inhibition of ζ-crystallin by coumarins: A structure-activity study

A structure-activity study was carried out to determine the important groups of coumarin derivatives in inhibiting the oxidoreductase activity of the camel lensζ-crystallin. Coumarin, 4-hydroxycoumarin, 7-hydroxy-4-methylcoumarin, dicoumarol, and warfarin were screened for their inhibitory effect onζ-crystallin activity. The sequence of potency for the inhibitors was dicoumarol > 4-hydroxycoumarin > warfarin ? coumarin. 7-Hydroxy-4-methylcoumarin was ineffective as an inhibitor. Only dicoumarol, 4-hydroxycoumarin, and warfarin were found to inhibit the oxidoreductase activity in micromolar ranges. All tested inhibitors seem to act in reversible and time-independent manner. Concentration causing 50% inhibition of the enzyme activity (IC ₅₀ value) was 34μM for dicoumarol, 76μM for 4-hydroxycoumarin, and approximately 515μM for warfarin, while 1 mM coumarin showed less than 10% inhibition. Kinetic analysis revealed inhibition of camel lensζ-crystallin by coumarin derivatives to occur in a competitive manner with respect to dichlorophenolindophenol (DCIP) as an electron acceptor and uncompetitive manner with respect to NADPH as an electron donor. TheK _i values were found to be 16μM for dicoumarol, 40μM for 4-hydroxycoumarin, and 220μM for warfarin. The structure-activity relationship of coumarin derivatives indicates that the phenolic hydroxyl group at the C-4 position in the coumarin skeleton is important for the maximal inhibition.     

Single-molecule atomic force microscopy force spectroscopy study of Aβ-40 interactions

Misfolding and aggregation of amyloid β-40 (Aβ-40) peptide play key roles in the development of Alzheimer's disease (AD). However, very little is known about the molecular mechanisms underlying these molecular processes. We developed a novel experimental approach that can directly probe aggregation-prone states of proteins and their interactions. In this approach, the proteins are anchored to the surface of the atomic force microscopy substrate (mica) and the probe, and the interaction between anchored molecules is measured in the approach-retraction cycles. We used dynamic force spectroscopy (DFS) to measure the stability of transiently formed dimers. One of the major findings from DFS analysis of α-synuclein (α-Syn) is that dimeric complexes formed by misfolded α-Syn protein are very stable and dissociate over a range of seconds. This differs markedly from the dynamics of monomers, which occurs on a microsecond to nanosecond time scale. Here we applied the same approach to quantitatively characterize interactions of Aβ-40 peptides over a broad range of pH values. These studies showed that misfolded dimers are characterized by lifetimes in the range of seconds. This value depends on pH and varies between 2.7 s for pH 2.7 and 0.1 s for pH 7, indicating that the aggregation properties of Aβ-40 are modulated by the environmental conditions. The analysis of the contour lengths revealed the existence of various pathways for dimer dissociation, suggesting that dimers with different conformations are formed. These structural variations result in different aggregation pathways, leading to different types of oligomers and higher-order aggregates, including fibrils.     

A study of the dynamic properties of membrane proteins using M?ssbauer spectroscopy

While studying the parameters of "narrow" and "broad" lines appearing in M?ssbauer spectra of undehydrated membrane proteins heated from 80 to 280 K it has been for the first time found for proteins that the behavior of the complete area of spectrum S does not differ from that of Debye-Waller factor. An abrupt decrease of quadrupole splitting value from delta = 0.7 mm/s to delta = 0 within the temperature range 220-270 K. Computation of the spectra with their division into 3 components responding respectively by heat, diffusion and conformational movement made possible explanation of all the evolutionary changes proceeding in them with the temperature rise. Preservation of the complete area of the spectrum S (T) is conditioned by the increase of the component responsive to conformational changes of Fe atom within 230-270 K. These movements "suppress" quadrupole splitting observed in the spectra at low temperatures. Dynamic mobility is considered in terms of the Fe atom movement in the biphase potential.     

Nanomechanical properties of MscL α helices: A steered molecular dynamics study

Gating of mechanosensitive (MS) channels is driven by a hierarchical cascade of movements and deformations of transmembrane helices in response to bilayer tension. Determining the intrinsic mechanical properties of the individual transmembrane helices is therefore central to understanding the intricacies of the gating mechanism of MS channels. We used a constant-force steered molecular dynamics (SMD) approach to perform unidirectional pulling tests on all the helices of MscL in M. tuberculosis and E. coli homologs. Using this method, we could overcome the issues encountered with the commonly used constant-velocity SMD simulations, such as low mechanical stability of the helix during stretching and high dependency of the elastic properties on the pulling rate. We estimated Young's moduli of the α-helices of MscL to vary between 0.2 and 12.5 GPa with TM2 helix being the stiffest. We also studied the effect of water on the properties of the pore-lining TM1 helix. In the absence of water, this helix exhibited a much stiffer response. By monitoring the number of hydrogen bonds, it appears that water acts like a ‘lubricant’ (softener) during TM1 helix elongation. These data shed light on another physical aspect underlying hydrophobic gating of MS channels, in particular MscL.     

Modulation of the activity of cytosolic phospholipase A2�� (cPLA2��) by cellular sphingolipids and inhibition of cPLA2�� by sphingomyelin

We examined the effect of the cellular sphingolipid level on the release of arachidonic acid (AA) and activity of cytosolic phospholipase A2α (cPLA2α) using two Chinese hamster ovary (CHO)-K1-derived mutants deficient in sphingolipid synthesis: LY-B cells defective in the LCB1 subunit of serine palmitoyltransferase for de novo synthesis of sphingolipid species, and LY-A cells defective in the ceramide transfer protein CERT for SM synthesis. When LY-B and LY-A cells were cultured in Nutridoma medium and the sphingolipid level was reduced, the release of AA stimulated by the Ca²⁺ ionophore {\"type\":\"entrez-nucleotide\",\"attrs\":{\"text\":\"A23187\",\"term_id\":\"833253\",\"term_text\":\"A23187\"}}A23187 increased 2-fold and 1.7-fold, respectively, compared with that from control cells. The enhancement in LY-B cells was decreased by adding sphingosine and treatment with the cPLA2α inhibitor. When CHO cells were treated with an acid sphingomyelinase inhibitor to increase the cellular SM level, the release of AA induced by {\"type\":\"entrez-nucleotide\",\"attrs\":{\"text\":\"A23187\",\"term_id\":\"833253\",\"term_text\":\"A23187\"}}A23187 or PAF was decreased. In vitro studies were then conducted to test whether SM interacts directly with cPLA2α. Phosphatidylcholine vesicles containing SM reduced cPLA2α activity. Furthermore, SM disturbed the binding of cPLA2α to glycerophospholipids. These results suggest that SM at the biomembrane plays important roles in regulating the cPLA2α-dependent release of AA by inhibiting the binding of cPLA2α to glycerophospholipids.     

Influence of 7α-hydroxycholesterol on sphingomyelin and sphingomyelin/phosphatidylcholine films - The Langmuir monolayer study complemented with theoretical calculations

Under pathological conditions, cholesterol oxidation products (oxysterols) appear in enhanced concentration in blood and cerebrospinal fluid, which leads to cytotoxic effect, especially in central nervous system. However, the mode of action of oxysterols on the membrane level has not been fully resolved. In this paper we have investigated the interaction between 7α- hydroxycholesterol, 7α-OH (one of the most abundant oxysterol in human body) and two major membrane lipids: sphingomyelin, SM (basic component of lipid rafts and nerve membrane) and 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine, POPC (main phospholipid of mammalian cell membranes). 7α-OH/SM mixtures may mimic pathologically changed lipid raft (ordered phase, L_O) while the SM/POPC system can model its surrounding (liquid-disordered phase, L_α). For our study, the Langmuir monolayer technique (based on registration of the surface pressure/area, π/A isotherms), complemented with surface visualization technique (Brewster angle microscopy, BAM) and theoretical calculations, have been employed. The observed affinity of 7α-OH to SM, which appears to be stronger than in cholesterol/SM system, indicates that cholesterol might be partially replaced in lipid rafts by its oxidized derivative. Its incorporation significantly increases rigidity of the system in relation to normal (cholesterol-containing) raft, which can disturb its proper functioning. On the other hand, the poor effect of this oxysterol on the raft's environment was observed.     

Monte Carlo study of the formation and conformational properties of dimers of Aβ42 variants

Small soluble oligomers, and dimers in particular, of the amyloid β-peptide (Aβ) are believed to play an important pathological role in Alzheimer's disease. Here, we investigate the spontaneous dimerization of Aβ42, with 42 residues, by implicit solvent all-atom Monte Carlo simulations, for the wild-type peptide and the mutants F20E, E22G and E22G/I31E. The observed dimers of these variants share many overall conformational characteristics but differ in several aspects at a detailed level. In all four cases, the most common type of secondary structure is intramolecular antiparallel β-sheets. Parallel, in-register β-sheet structure, as in models for Aβ fibrils, is rare. The primary force driving the formation of dimers is hydrophobic attraction. The conformational differences that we do see involve turns centered in the 20-30 region. The probability of finding turns centered in the 25-30 region, where there is a loop in Aβ fibrils, is found to increase upon dimerization and to correlate with experimentally measured rates of fibril formation for the different Aβ42 variants. Our findings hint at reorganization of this part of the molecule as a potentially critical step in Aβ aggregation.     

Stabilization of trypsin by chemical modification with β-cyclodextrin monoaldehyde

The monoaldehyde derivative of -cyclodextrin was attached to trypsin via reductive alkylation with NaBH₄. The thermostability was enhanced from 49.5 °C to 60 °C for modified trypsin. The activation free energy of thermal inactivation at 50 °C was increased by 3.2 kJ mol^–1. The conjugated enzyme retained 100% of its initial activity after 3 h incubation at pH 9.