Decrease In Positive Charge Research Articles

Tau PTM Profiles Identify Patient Heterogeneity and Stages of Alzheimer’s Disease

To elucidate the role of Tau isoforms and post-translational modification (PTM) stoichiometry in Alzheimer's disease (AD), we generated a high-resolution quantitative proteomics map of 95 PTMs on multiple isoforms of Tau isolated from postmortem human tissue from 49 AD and 42 control subjects. Although Tau PTM maps reveal heterogeneity across subjects, a subset of PTMs display high occupancy and frequency for AD, suggesting importance in disease. Unsupervised analyses indicate that PTMs occur in an ordered manner, leading to Tau aggregation. The processive addition and minimal set of PTMs associated with seeding activity was further defined by analysis of size-fractionated Tau. To summarize, features in the Tau protein critical for disease intervention at different stages of disease are identified, including enrichment of 0N and 4R isoforms, underrepresentation of the C terminus, an increase in negative charge in the proline-rich region (PRR), and a decrease in positive charge in the microtubule binding domain (MBD).

Fabrication of Aptamer-Immobilized Multi-Target Field-Effect Transistor Biosensor for Sensing Mental Stress

The sensing of biomarkers in the body is very effective for diagnosis of disease and monitoring of human health condition. However, blood sampling of mental stress markers is stressful for those who do not feel serious health concerns when they want to check only their own stress level. We need to measure stress markers noninvasively in our daily lives. Saliva is an ideal biological sample to be taken noninvasively. α-amylase and cortisol are known as stress markers in saliva. Since individual differences in stress response are large, it is important to simultaneously detect multiple markers and evaluate the stress level. In this study, we attempted to fabricate two field effect transistor (FET) biosensors using aptamers against α-amylase and cortisol as indexes of stress. Our purpose was to investigate the characteristics of sensing two types of biomarkers, a protein and a steroid molecule, using aptamer-immobilized FET biosensors. The aptamer against α-amylase and the one against cortisol were obtained after eight rounds of selection by SELEX method from an initial DNA library. The gate insulator (SiO2) of FET was modified with 3-aminopropyltriethoxysilane, followed by addition of glutaraldehyde. Each of two aptamers, which are terminated with amino group, was immobilized on the thus-prepared surface of insulator. We detected α-amylase and cortisol in phosphate buffer using the aptamer against α-amylase and the one against cortisol respectively. An increase in the magnitude of response was observed with an increase of α-amylase concentration in the range between 1 nmol/dm3 and 100 nmol/dm3. FET sensor responded as a gate voltage shift to the change in charge on the gate insulator surface. The observed response was suggested the binding of negatively charged α-amylase (isoelectric point = 6.34) to the aptamer. Though cortisol is an electrically neutral molecule, an increase in the magnitude of response was observed with an increase of cortisol concentration in the range between 1 μmol/dm3 and 1 mmol/dm3. It was a similar behavior toward the increase of negative charge or the decrease of positive charge. The phosphate groups of DNA aptamers and their counter ions have an electrical charge on the gate insulator. This suggests that the cortisol aptamer contracted and its negative charge penetrated Debye length or that the counter ion bound to the aptamer beforehand was removed after the association of cortisol. The concentration of α-amylase in saliva is 1 - 3 μmol/dm3. The sensitivity of this α-amylase sensor is at a practical level. The concentration of cortisol in saliva is 3 - 11 nmol/dm3. This cortisol FET sensor requires optimization of aptamer and refinement of the device for practical application. The quantitative detection of α-amylase and cortisol using aptamer-immobilized FET sensor was achieved. This sensor can be sensitive to a structural change of aptamer induced by the target binding. It was demonstrated that the detection of the neutral target molecule is possible. AcknowledgementThis work is supported by Adaptable and Seamless Technology transfer Program through targetdriven R&D (A-STEP), and the Center of Innovation S&T-Based Radical Innovation & Entrepreneurship Program (COI-STREAM), both from the Japan Science and Technology Agency (JST) and the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

Potentiometric Sensing of Aspirin Metabolite in Human Plasma and Pharmaceutical Preparations Using Co(III)‐complex Based Electrodes: Experimental and Quantum Chemical Calculations

AbstractThree novel poly vinyl chloride (PVC) (A), carbon paste (CP) (B), and coated glassy carbon‐MWCNT (CGC) (C) salicylate (sal−) sensors based on new synthesized [Co(L2Cl)Cl3(H2O)] ⋅ H2O complex (L2Cl=(1H‐benzimidazol‐2‐ylmethyl)‐N‐(2‐chloro‐phenyl)‐ amine)), o‐nitrophenyloctyl ether as a mediator and tridodecylmethylammonium chloride as a cationic additive were successfully used for determination of sal− in human plasma and pharmaceutical formulations. The sal−‐sensors exhibited enhanced sensitivity with slope of −63.5, −60.5 and −58.9 mV/decade and detection limit of 1.0×10−5, 4.0×10−7, and 1.0×10−6 mol L−1 for A–C sensors respectively. Quantum chemical calculations were carried out by HF and DFT/B3LYP methods to explore and investigate the interaction between the receptor and the different anions. The intermolecular H‐bond created between the uncoordinated CO of salicylate group and the secondary amino group in the complex is the key factor of the selectivity of the proposed sensor. A linear relation is established between the natural charge on the Co center and the value of the binding energy, where the decrease in positive charge is associated by an increase in the anion binding energy.

Controlling the charge of pH-responsive redox hydrogels by means of redox-silent biocatalytic processes. A biocatalytic off/on switch

Coupling of redox-silent biocatalytic processes for analyte detection with enzyme-catalyzed redox reactions for signal generation is proposed by the modulation of electrostatic interactions between a pH-responsive polymer and a redox enzyme to control the off–on transition for electrochemical signal generation. Glassy carbon electrodes are modified with a poly(vinyl)imidazole Os(bipyridine)2Cl redox hydrogel film entrapping urease and PQQ-dependent glucose dehydrogenase, while glucose is present in the solution. The off–on transition is based on the detection of urea as model analyte which is hydrolyzed to ammonia by urease within the hydrogel film concomitantly increasing the local pH value thus invoking deprotonation of the imidazole groups at the polymer backbone. The decrease of positive charges at the polymer decreases electrostatic repulsion between the polymer and the positively charged PQQ-dependent glucose dehydrogenase. Hence, electron transfer rates between polymer-bound Os complexes and PQQ inside the enzyme are enhanced activating electrocatalytic oxidation of glucose. This process generates the electrochemical signal for urea detection.

Linear Free-Energy Relationship and Rate Study on a Silylation-Based Kinetic Resolution: Mechanistic Insights

The substituent effect of different p-substituted triphenylsilyl chlorides on silylation-based kinetic resolutions was explored. Electron-donating groups slow down the reaction rate and improve the selectivity, while electron-withdrawing groups increase the reaction rate and decrease the selectivity. Linear free-energy relationships were found correlating both selectivity factors and initial rates to the σ(para) Hammett parameters. A weak correlation of selectivity factors to Charton values was also observed when just alkyl substituents were employed but was nonexistent when substituents with more electronic effects were incorporated. The rate data suggest that a significant redistribution of charge occurs in the transition state, with an overall decrease in positive charge. The linear free-energy relationship derived from selectivity factors is best understood by the Hammond postulate. Early and late transition states describe the amount of substrate participation in the transition state and therefore the difference in energy between the diastereomeric transition states of the two enantiomers. This work highlights our efforts toward understanding the mechanism and origin of selectivity in our silylation-based kinetic resolution.

The Effect of PS Content on the Ability of Natural Membranes to Fuse with Positively Charged Liposomes and Lipoplexes

Supramolecular aggregates containing cationic lipids have been widely used as transfection mediators due to their ability to interact with negatively charged DNA molecules and biological membranes. First steps of the process leading to transfection are partly electrostatic, partly hydrophobic interactions of liposomes/lipoplexes with cell and/or endosomal membrane. Negatively charged compounds of biological membranes, namely glycolipids, glycoproteins and phosphatidylserine (PS), are responsible for such events as adsorption, hemifusion, fusion, poration and destabilization of natural membranes upon contact with cationic liposomes/lipoplexes. The present communication describes the dependence of interaction of cationic liposomes with natural and artificial membranes on the negative charge of the target membrane, charges which in most cases were generated by charging the PS content or its exposure. The model for the target membranes were liposomes of variable content of PS or PG (phosphatidylglycerol) and erythrocyte membranes in which the PS and other anionic compound content/exposure was modified in several ways. Membranes of increased anionic phospholipid content displayed increased fusion with DOTAP (1,2-dioleoyl-3-trimethylammoniumpropane) liposomes, while erythrocyte membranes partly depleted of glycocalix, its sialic acid, in particular, showed a decreased fusion ability. The role of the anionic component is also supported by the fact that erythrocyte membrane inside-out vesicles fused easily with cationic liposomes. The data obtained on erythrocyte ghosts of normal and disrupted asymmetry, in particular, those obtained in the presence of Ca(2+), indicate the role of lipid flip-flop movement catalyzed by scramblase. The ATP-depletion of erythrocytes also induced an increased sensitivity to hemoglobin leakage upon interactions with DOTAP liposomes. Calcein leakage from anionic liposomes incubated with DOTAP liposomes was also dependent on surface charge of the target membranes. In all experiments with the asymmetric membranes the fusion level markedly increased with an increase of temperature, which supports the role of membrane lipid mobility. The decrease in positive charge by binding of plasmid DNA and the increase in ionic strength decreased the ability of DOTAP liposomes/lipoplexes to fuse with erythrocyte ghosts. Lower pH promotes fusion between erythrocyte ghosts and DOTAP liposomes and lipoplexes. The obtained results indicate that electrostatic interactions together with increased mobility of membrane lipids and susceptibility to form structures of negative curvature play a major role in the fusion of DOTAP liposomes with natural and artificial membranes.

Substituent effects on the barrier to carbamate C–N rotation

Seven aryl-substituted t-butyl N-methyl- N-aryl carbamates were prepared, and in each case, the barrier to C–N bond rotation, ΔG ‡ , was determined in CDCl 3 solution using variable temperature NMR. A linear free energy relationship is observed between ΔG ‡ and the electronic stabilization effect of the substituent on the N-aryl ring. More specifically, electron donating groups increase ΔG ‡ , whereas withdrawing groups decrease ΔG ‡ . A plot against σ– was more linear ( r 2=0.96), than a plot against σ ( r 2=0.90) or σ+ ( r 2=0.88) and a value of ρ=1.76 was obtained at 243 K. Thus, rotation about the carbamate C–N bond in weakly polar chloroform involves a decrease in positive charge on the nitrogen.

Effect of low-molecular-weight organic anions on surface charge of variable charge soils

Low-molecular-weight (LMW) organic acids exist widely in soils and have been implicated in many soil processes. In the present paper, the effect of the anions of four low-molecular-weight organic acids on the surface charge of three variable charge soils was investigated. The results showed that the presence of organic anions led to an increase in negative charge and a decrease in positive charge. Positive charges decreased to a larger extent than negative charges. The effect of different anions on surface charge followed the order citrate > malate > oxalate > acetate. For hyper-rhodic ferrasol and rhodic ferrasol, the change of positive charge decreased with the increase in pH, while that of negative charge increased with the increase in pH. Among different soils the extent of change in surface charge was related to their iron oxides content. When free iron oxides were removed from the soil, the effect of organic anions on surface charge decreased sharply. These findings may be of practical significance for variable charge soils low in nutrient-retaining capacity by increasing the retaining capacity for cations such as potassium and calcium considerably but decreasing that for anions such as nitrate remarkably.

Coordination of boron in alkali borosilicate glasses using XANES

Glasses in the systems Na 2O–B 2O 3–SiO 2 (with 50, 60 and 70 mol% SiO 2) and K 2O–B 2O 3–SiO 2 (with 50 mol% SiO 2) have been prepared by melt quenching in air and studied using B K-edge X-ray absorption near-edge structure (XANES) spectroscopy to estimate the proportion of four-fold coordinated (tetrahedral) boron. The B K-edge XANES spectra are characterized by three prominent features: a sharp peak at ∼194 eV (the edge feature of trigonal B), a broader peak at 198–200 eV (the edge feature of tetrahedral B), and a broad peak at 201–204 eV, which is associated with contributions from both trigonal BO 3 and tetrahedral BO 4 groups. Using the fluorescence yield method to collect spectra, the proportion of tetrahedral B obtained for sodium borosilicate glasses is in good agreement with previous wide line 11B NMR results for R (molar Na 2O/B 2O 3) in the range 0–1.0. The yield of tetrahedral B is consistent with the Bray et al. model for structural change in borate and borosilicate glasses, and indicates that the onset of depolymerization of silicate entities is at about R=0.33. The XANES peaks shift systematically to lower energy with addition of Na 2O, reflecting a progressive decrease in positive charge on absorber atoms. For the first time, small amounts (∼1%) of tetrahedral B have been detected in binary B 2O 3–SiO 2 glasses. Glass particles have slightly more tetrahedral B in surface and near-surface layers than in the bulk interior.

A novel mutation in the gene for the adult skeletal muscle sodium channel alpha-subunit (SCN4A) that causes paramyotonia congenita of von Eulenburg.

Paramyotonia congenita (PMC) of von Eulenburg is an autosomal dominant muscular disease characterized by exercise- and cold-induced myotonia and weakness. To date, 18 missense mutations in the adult skeletal muscle sodium channel alpha-subunit (SCN4A) gene have been identified to cause a spectrum of muscular diseases, including PMC of von Eulenburg, PMC without cold paralysis, potassium-aggravating myotonia, and hyperkalemic periodic paralysis. However, no obvious correlations can be made between the location or nature of amino acid substitutions in SCN4A and its clinical phenotypes. To describe clinical and genetic features of a family with PMC of von Eulenburg. A Japanese family with cold-induced myotonia and weakness was diagnosed as having PMC of von Eulenburg. This phenotype was identified to be caused by a novel mutation that substituted a glutamic acid residue for a highly conserved glycine residue in the fourth transmembrane segment (S4) of domain IV. This predicted a decrease in positive charge specific for the S4. In addition to the G1456E identified in this study, 4 mutations that cause a decrease in positive charge in the S4/D4 are associated with the phenotype of PMC of von Eulenburg. This provides an important genotype-phenotype correlation in sodium channelopathies.

A new model for the agonistic binding site on the histamine H 2-receptor: The catalytic triad in serine proteases as a model for the binding site of

The historical model for the agonistic binding site on the histamine H 2-receptor is based on a postulated activation mechanism: it has been suggested that the histamine monocation binds to the histamine H 2-receptor via the formation of three hydrogen bonds. The cationic ammonium group in the side chain and the —NH— group in the π-position of the imidazole act as proton donors, whereas the N— atom in the π-position of the imidazole acts as a proton acceptor. Participation of the ammonium group in H-bonding with a presumed negative charge on the receptor leads to a decrease in positive charge, which is thought to induce a tautomeric change in the imidazole ring system from N τ-H to N π-H. A consequence of this tautomeric shift is the donation of a proton from the receptor to the agonist on one side, while on the other side a proton is donated from the agonist to the receptor. The proposed tautomeric shift has been suggested to trigger the H 2-stimulating effect. However, this model for the constitution of the agonistic binding site and the accessory activation mechanism cannot explain the weak histamine H 2-activity of β-histine and the activity of several other recently synthesized H 2-agonists. Based on a thorough literature study and with the aid of molecular electrostatic potentials (MEPs) we demonstrate that the sulphur atom present in histamine H 2-agonists as dimaprit and 2-amino-5-(2-aminoethyl)thiazole does not function as a proton acceptor, which implicitly means that a tautomeric shift is not a prerequisite for H 2-stimulation. As a consequence, the model for the agonistic binding site is adjusted, resulting in a strong resemblance to the nature and orientation of the amino acids constituting the catalytic triad in serine proteases. Within this concept, the N π-H tautomer of histamine is the biologically active form, in contrast with the existing model in which the N τ-H tautomer is the active form.

Substitution and properties of Bi/Pb-based ferrates of 3212-type

Bi-based ferrates of type 3212 with three rocksalt-like layers between the Fe containing perovskite slabs of general formula (Bi, Pb, Sr)3Sr3Fe2O10+z are characterized by a hole concentration of about 0.25 h+/Fe ion. According to investigations by XRD, SEM, EDXA, Mössbauer, magnetic, electrical, and vibrational spectroscopic measurements, charge delocalization by hopping conduction is present at room temperature whereas at low temperatures a transition to antiferromagnetism with charge localization takes place. Increase or decrease of positive charge by partial substitution La3+ → Sr2+ or Pb2+ → Bi3+ is simply compensated by an insertion or depletion of oxygen from the rocksalt layers and no exchange of carriers between the perovskite slabs and the rocksalt layer is detectable.

Poliovirus chimeras expressing sequences from the principal neutralization domain of human immunodeficiency virus type 1.

Sequences from the principal neutralization domain of human immunodeficiency virus type 1 (HIV-1) strain LAI or RF have been expressed in antigenic site 1 of the capsid of the Sabin strain of poliovirus type 1. A number of the resulting chimeras were viable. Viable variants bearing mutations within the insertion site spontaneously arose from several nonviable chimeras. In general, these mutations result in a decrease in positive charge in the substituted antigenic site 1. Two of the chimeras were genetically stable and have been further characterized. Both chimeras were neutralized by various HIV-1 neutralizing antibodies. In rabbits, both chimeras produced high levels of antibodies which react with HIV-1 gp120/160 in immunoprecipitation and enzyme-linked immunosorbent assays. One of the chimeras (HIV-1LAI) produced a significant but weak HIV-1 neutralizing response.

Investigation of the selectivity of maltoporin channels using mutant LamB proteins: mutations changing the maltodextrin binding site

Wild-type and seven mutant maltoporins were purified and their channel-forming activities studied after reconstitution into black lipid membranes. The proteins were assayed for alterations at the maltodextrin binding site by measuring the sugar-dependent blockage of ion flux through these channels. Some substitutions (R8H, W74R) caused reduced channel affinity for all maltodextrins without changing single channel conductivities. The channel with a Glyser insertion after residue 9 was also poorly blocked by sugars but unique to this protein, the channel showed a striking, almost exponential increase of affinity with increasing maltodextrin chain length. In mutants with AspPro insertions after residues 79 and 183, there was an increase in affinity for glucose and maltose but not longer maltodextrins. The additional negative charge in the AspPro insertion mutants increased the cation selectivity of maltoporin channels, as did the decrease in positive charge resulting from the R8H substitution. A mutant with a W120C substitution also showed an increased affinity for glucose and maltose but reduced affinity for longer maltosaccharides. In contrast, a Y118F substitution resulted in an 8-fold increase in maltotriose affinity, but lesser improvements for other sugars. These results are interpreted to reflect changes in subsites contributing to an extended binding site within the channel, which in turn determines the overall sugar affinity of maltoporin.

Adsorption of sulphate and fluoride by variable charge soils

SUMMARYThe adsorption of sulphate and fluoride by three variable charge soils was studied. Adsorption increased with increase in the amount of sulphate added at constant pH, and decreased with increase of pH.The ratios of the amount of released OH−to that of the adsorbed SO2‐4 at pH 5–0 were 0.12, 0.14 and 0.20 for the three soils, respectively, much lower than the corresponding OH−/F− ratios which ranged from 0.3 to 1.0. For a ferric acrisol the OH− released accounted, on average, for only 15% of the SO2‐4 adsorbed, leaving more than 60% to be explained by the decrease in positive charge and the increase in negative charge carried by the soil.

Mechanism of Sulfate Adsorption by Kaolinite

AbstractSulfate adsorption on kaolinite was followed at 0.7 μeq/ml to 99 μeq/ml solution concentrations at 30°C and at pH 6.0, and the amount of OH~ ions released and the change in surface charge were determined. Sulfate was adsorbed at positive and neutral sites by displacing OH2 and OH− groups, respectively. Adsorption of sulfate occurred predominantly at positive sites at low (0.7 μeq/ml to 0.9 /μeq/ml) solution concentrations, whereas at higher solution concentrations, the proportion of the sulfate adsorbed at the neutral sites increased, varying from 51% at 4.9 μeq/ml to 68% at 99 μeq/ml. The form of sulfate bonding was apparently governed by the level of the positive charge on the clay surface. Higher positive charge at low and intermediate levels of sulfate saturation resulted in the adsorption of sulfate as a divalent anion by forming a 6-member ring with surface Al. With a decrease in positive charge at higher levels of adsorption, the sulfate ion formed both monodentate and bidentate complexes.

7] Measurement of nonenzymatic protein glycosylation

This chapter discusses the methodology for the detection of nonenzymatic protein glycosylation. It describes proteins other than hemoglobin, which are enzymatically glycosylated. In the nonenzymatic glycosylation reaction, glucose and other aldoses and ketoses react with unprotonated amino groups to initially form a Schiff's base (aldimine) which can undergo the Amadori rearrangement to the corresponding 1-amino-1-deoxy-2-keto compound (ketoamine). The charge-dependent separations employing ion exchange chromatography, isoelectric focusing, and agar gel electrophoresis rely on the decrease in positive charge caused by glycosylation of the N-terminal amino groups of the β chains of hemoglobin. Glycosylation at all other sites does not alter the charge sufficiently to allow resolution of adducts from unglycosylated hemoglobin. On ion exchange chromatography, the hemoglobins glycosylated at the N-terminus of α chains and at some ɛ-amino groups elute in the leading edge of the main HbA peak. Total hemoglobin glycosylation may be determined chromatographically with boronate affinity chromatography or by one of several chemical techniques. Under certain conditions, the nonenzymatic glycosylation may even be determined in proteins which are also enzymatically glycosylated with these techniques.

Charge distributions and Chemical effects. XII. A unifying concept

Major inconsistencies which are currently acknowledged in discussions involving atomic charges, inductive effects, 13C nmr shifts, and stability of carbonium ions are removed (i) by the use of an appropriate definition of charges and (ii) by the recognition that in alkanes and alkyl carbonium ions any decrease in positive charge at carbon atoms results in a downfield 13C shift. Methyl appears to be less electron withdrawing than hydrogen, and stability of carbonium ions is associated with dispersion of positive charge at the carbonium center, in line with the more traditional views which are repeatedly challenged in recent literature.

Research on 1, 2, 4-triazoles

The stability of sulfides and sulfones of 1-aryltetrazoles and 4-aryl-1, 2, 4-triazoles depends on the acceptor character of the heterocyclic ring. Unlike tetrazole sulfides, triazole sulfides do not undergo hydrolysis, Tetrazole sulfones are more readily hydrolyzed than triazole ones. When an electron-donor substituent is introduced into the p-position of the phenyl ring, the rate of hydrolysis is cut. Neither triazole nor tetrazole sulfides and sulfones, not arylated at a nitrogen atom, are hydrolyzed by alkali, because of a partial decrease in positive charge at the carbon atom of the sulfoazomethine group through formation of an anion with a sextet of π-electrons in the ring. Hydrolysis of sulfides and sulfones can conveniently be used to prepared 1-aryltetrazolinones-5 and 4-aryl-1, 2, 4-triazolinones-3.