Nonlinear Curve-fitting Program Research Articles

Application of powder XRD to compute crystallite shape of cotton fibers from different countries

The structural properties of the cotton fiber play a significant role to deliver the best product to the consumer. In view of this, we attempted to obtain the structural properties of varieties of cotton fiber which are cultivated in three different countries. The Powder X-ray Diffraction (PXRD) data of these fibers are incorporated into a non-linear curve fitting program called Peakfit for the accurate peak analysis and conclusive findings of peaks. These data were again employed to Checkcell to identify unit cell parameters. The Debye Scherrer formula is used to compute the crystallite size. The shape of the Ordered Region has been obtained by transformation from cartesian to polar coordinates. These shapes show a multidimensional topography and strongly depend on the environment where the cotton is cultivated. The idea of this shape of ordered region is essentially required for many textile and biomedical industry applications.

Metropolis-Hastings Markov Chain Monte Carlo Approach to Simulate van Genuchten Model Parameters for Soil Water Retention Curve

The soil water retention curve (SWRC) is essential for assessing water flow and solute transport in unsaturated media. The van Genuchten (VG) model is widely used to describe the SWRC; however, estimation of its effective hydraulic parameters is often prone to error, especially when data exist for only a limited range of matric potential. We developed a Metropolis-Hastings algorithm of the Markov chain Monte Carlo (MH-MCMC) approach using R to estimate VG parameters, which produces a numerical estimate of the joint posterior distribution of model parameters, including fully-quantified uncertainties. When VG model parameters were obtained using complete range of soil water content (SWC) data (i.e., from saturation to oven dryness), the MH-MCMC approach returned similar accuracy as the widely used non-linear curve-fitting program RETC (RETention Curve), but avoiding non-convergence issues. When VG model parameters were obtained using 5 SWC data measured at matric potential of around −60, −100, −200, −500, and −15,000 cm, the MH-MCMC approach was more robust than the RETC program. The performance of MH-MCMC are generally good (R2 > 0.95) for all 8 soils, whereas the RETC underperformed for coarse-textured soils. The MH-MCMC approach was used to obtain VG model parameters for all 1871 soils in the National Cooperative Soil Characterization dataset with SWC measured at matric potentials of −60 cm, −100 cm, −330 cm, and −15,000 cm; the results showed that the simulated SWC by MH-MCMC model were highly consistent with the measured SWC at corresponding matric potential. Altogether, our new MH-MCMC approach to solving the VG model is more robust to limited coverage of soil matric potential when compared to the RETC procedures, making it an effective alternative to traditional water retention solvers. We developed an MH-MCMC code in R for solving VG model parameters, which can be found at the GitHub repository.

SLAM-MS: Mutation scanning of stem-loop amplicons with TaqMan probes by quantitative DNA melting analysis

DNA Melting Analysis (DMA) with a TaqMan probe covering the mutation “hot spot” is a simple, sensitive, and “closed tube” method of mutation detection. However, DMA requires asymmetric PCR to produce single-stranded amplicons capable of interacting with TaqMan probes. This makes quantitative analysis impossible owing to low amplification efficiency. Moreover, bi-strand mutation detection necessitates two independent PCRs. The SLAM-MS (Stem-Loop AMplicon Mutation Scanning) assay, in which symmetric PCR is performed using primers with 5'-universal primer sequence (UPS), has been developed to detect KRAS mutations. Some of the resulting amplicons, sense and antisense, adopt single-stranded stem-loop conformation and become unable to renature, but able to hybridize with TaqMan probes. Hybrids of stem-loops and complementary TaqMan probes are suitable for melting analysis and simultaneous bi-strand mutation scanning. In addition, the areas under the melting peaks are determined by the PeakFit software, a non-linear iterative curve fitting program, to evaluate the wild-type/mutant allele ratio. Thus, the SLAM-MS assay permits quantification of both the number of copies of the target sequence and the percentage of mutant alleles. For mutant enrichment, the SLAM-MS assay uses TaqMan probes as PCR blocking agents allowing an ~10 times higher mutation detection sensitivity than High Resolution Melting (HRM) assay.

Comparison of optical absorption and thermoluminescence in LiF:Mg, TI (TLD-100) following irradiation by high energy protons and 90Sr/90Y beta rays

The optical absorption (OA) energy spectrum and thermoluminescence (TL) glow curve characteristics of LiF:Mg, Ti (TLD-100) samples following 90Sr/90Y beta ray irradiation and high energy proton irradiation are compared for the first time. The beta ray irradiations were carried at room temperature at a dose rate in LiF of approximately 0.13 Gy min−1. Proton irradiations were carried out at energies of 20 MeV, 40 MeV and 58 MeV with initial stopping powers of 5.5, 3.2 and 2.3 keV μm−1 respectively. Proton escaping the TL detectors had average energies 55.9, 37.1, 14.4 MeV and the corresponding stopping power in LiF 2.43, 3.36, 7.19 keV μm−1 respectively. All proton irradiations were carried out at a dose of 1124 Gy in LiF and the beta irradiations at a dose of 970 Gy in LIF. The OA spectra were deconvoluted with Gaussian Peak Shapes using a commercial “Peak-Fit” non-linear curve fitting program from Jandel Scientific. The Gaussian bands are characterized by the two parameters of band energy and width. The glow curves were deconvoluted using the Ben Gurion University mixed-order kinetics program. In the analysis first-order kinetics glow peak shapes were employed. The major difference between the two spectra is in the optical density of the F band at 5.08 eV; 0.17 compared to an average value of 0.33 following beta and proton irradiation respectively. The relative intensity, protons to betas, of the other OA bands are remarkably similar within the experimental errors and indicate that the traps associated with these OA bands are not created by the irradiation. It is demonstrated that proton irradiation of LiF:Mg, Ti (TLD-100) creates F centers with 75% greater efficiency than 90Sr/90Y beta particles. This finding lends further support to the conclusion that track structure theory is unable to accurately predict proton relative efficiencies in LiF:Mg, Ti The results are also interpreted in the framework the spatially correlated trapping center/luminescent center model for composite peak 5 in LiF:Mg,Ti.

Postmortem interval estimation: a novel approach utilizing gas chromatography/mass spectrometry-based biochemical profiling.

While the molecular mechanisms underlying postmortem change have been exhaustively investigated, the establishment of an objective and reliable means for estimating postmortem interval (PMI) remains an elusive feat. In the present study, we exploit low molecular weight metabolites to estimate postmortem interval in mice. After sacrifice, serum and muscle samples were procured from C57BL/6J mice (n = 52) at seven predetermined postmortem intervals (0, 1, 3, 6, 12, 24, and 48 h). After extraction and isolation, low molecular weight metabolites were measured via gas chromatography/mass spectrometry (GC/MS) and examined via semi-quantification studies. Then, PMI prediction models were generated for each of the 175 and 163 metabolites identified in muscle and serum, respectively, using a non-linear least squares curve fitting program. A PMI estimation panel for muscle and serum was then erected which consisted of 17 (9.7%) and 14 (8.5%) of the best PMI biomarkers identified in muscle and serum profiles demonstrating statistically significant correlations between metabolite quantity and PMI. Using a single-blinded assessment, we carried out validation studies on the PMI estimation panels. Mean ± standard deviation for accuracy of muscle and serum PMI prediction panels was -0.27 ± 2.88 and -0.89 ± 2.31 h, respectively. Ultimately, these studies elucidate the utility of metabolomic profiling in PMI estimation and pave the path toward biochemical profiling studies involving human samples.

Novel Structural and Functional Insights into M3 Muscarinic Receptor Dimer/Oligomer Formation

Class A G protein-coupled receptors (GPCRs) are able to form homodimers and/or oligomeric arrays. We recently proposed, based on bioluminescence resonance energy transfer studies with the M3 muscarinic receptor (M3R), a prototypic class A GPCR, that the M3R is able to form multiple, structurally distinct dimers that are probably transient in nature (McMillin, S. M., Heusel, M., Liu, T., Costanzi, S., and Wess, J. (2011) J. Biol. Chem. 286, 28584-28598). To provide more direct experimental support for this concept, we employed a disulfide cross-linking strategy to trap various M3R dimeric species present in a native lipid environment (transfected COS-7 cells). Disulfide cross-linking studies were carried out with many mutant M3Rs containing single cysteine (Cys) substitutions within two distinct cytoplasmic M3R regions, the C-terminal portion of the second intracellular loop (i2) and helix H8 (H8). The pattern of cross-links that we obtained, in combination with molecular modeling studies, was consistent with the existence of two structurally distinct M3R dimer interfaces, one involving i2/i2 contacts (TM4-TM5-i2 interface) and the other one characterized by H8-H8 interactions (TM1-TM2-H8 interface). Specific H8-H8 disulfide cross-links led to significant impairments in M3R-mediated G protein activation, suggesting that changes in the structural orientation or mobility of H8 are critical for efficient receptor-G protein coupling. Our findings provide novel structural and functional insights into the mechanisms involved in M3R dimerization (oligomerization). Because the M3R shows a high degree of sequence similarity with many other class A GPCRs, our findings should be of considerable general interest.

Ion-specific Effects on Prion Nucleation and Strain Formation

Ordered, fibrous, self-seeding aggregates of misfolded proteins known as amyloids are associated with important diseases in mammals and control phenotypic traits in fungi. A given protein may adopt multiple amyloid conformations, known as variants or strains, each of which leads to a distinct disease pattern or phenotype. Here, we study the effect of Hofmeister ions on amyloid nucleation and strain generation by the prion domain-containing fragment (Sup35NM) of a yeast protein Sup35p. Strongly hydrated anions (kosmotropes) initiate nucleation quickly and cause rapid fiber elongation, whereas poorly hydrated anions (chaotropes) delay nucleation and mildly affect the elongation rate. For the first time, we demonstrate that kosmotropes favor formation of amyloid strains that are characterized by lower thermostability and higher frangibility in vitro and stronger phenotypic and proliferation patterns effectively in vivo as compared with amyloids formed in chaotropes. These phenomena point to inherent differences in the biochemistry of Hofmeister ions. Our work shows that the ionic composition of a solution not only influences the kinetics of amyloid nucleation but also determines the amyloid strain that is preferentially formed.

Hydraulic properties of characteristic horizons depending on relief position and structure in a hummocky glacial soil landscape

The hummocky ground moraine soil landscape forms a spatial continuum of more or less eroded and depositional soils developed from glacial till under intensive agricultural cultivation. Measurements of soil hydraulic properties in the laboratory on soil cores are mostly limited to some characteristic horizons. However, these horizons can vary in thickness or structural and pedological development depending on relief position. This paper compares soil hydraulic properties of the same soil horizons sampled at different relief positions in a single field representing various degrees of soil erosion/deposition. Water retention curves were determined from undisturbed core samples using sand and kaolin beds with hanging water column and pressure chambers, and the unsaturated hydraulic conductivity using the double-membrane apparatus. Data were fitted to the van Genuchten–Mualem function (VGM) using the nonlinear curve fitting program RETC. The desorption water retention curves for the soil horizons were different and depended on the soil structural development that could be related with the intensity of erosion history at each landscape position. The greatest differences in hydraulic functions were found for the E, Bt, and C horizons. The fitted soil water retention curves reflected these differences mainly in the values of the VGM curve parameters n and θs. The landscape features that have the strongest differentiating effect are related to erosion and distance towards the water table. The results can help improving pedotransfer approaches for the estimation of spatially distributed hydraulic parameters for modelling the water movement in hummocky soil landscapes as basis for establishing landscape scale water and element balances.

Kinetic mechanism and some properties of glucose-6-phosphate dehydrogenase from sheep brain cortex

Objective: Glucose-6-phosphate dehydrogenase is an important key enzyme which catalyzes the first oxidative step of the pentose phosphate pathway. The objectives of this study are to determine some properties and kinetic mechanism of glucose-6-phosphate dehydrogenase. Method: In this study we used the enzyme that was purified from sheep brain cortex. The kinetic analysis and other studies were performed within three days after the purification to prevent any loss of enzyme activity. Results: The subunit molecular weight was determined as 61.2 kDa by SDS-PAGE and 64.5 kDa by Sephadex G-200 gel filtration chromatography. The activation energy (Ea) of the reaction was calculated from the Arrhenius plot as 6.689 kcal/mol. We have calculated the temperature coefficient as 1.913 from the integrated form of the Arrhenius equation (for the temperatures between 30 - 40 oC). Optimum pH of the enzyme was determined as 8. Kinetic constants estimated by a nonlinear curve-fitting program are as follows: Vm= 2.182 ± 0.064 mmol/min/mg enzyme; Km NADP+ = 0.064 ± 0.001 mM; Km G6P = 0.0729 ± 0.006 mM; Ki G6P = 0.074 ± 0.003 mM; Ki NADP+ = 0.056 ± 0.001mM. Conclusion: Sheep brain cortex glucose-6-phosphate dehydrogenase exhibits classical Michaelis-Menten kinetics. Product inhibition studies were undertaken to distinguish the type of the mechanism. We have found that G6PD enzyme obeys 'Theorell-Chance' mechanism. The kinetic behavior, molecular weight, optimum temperature and pH of the enzyme were in accordance with our previous studies.

Constitutive Internalization of G Protein-coupled Receptors and G Proteins via Clathrin-independent Endocytosis

Although agonist-dependent endocytosis of G protein-coupled receptors (GPCRs) as a means to modulate receptor signaling has been widely studied, the constitutive endocytosis of GPCRs has received little attention. Here we show that two prototypical class I GPCRs, the beta2 adrenergic and M3 muscarinic receptors, enter cells constitutively by clathrin-independent endocytosis and colocalize with markers of this endosomal pathway on recycling tubular endosomes, indicating that these receptors can subsequently recycle back to the plasma membrane (PM). This constitutive endocytosis of these receptors was not blocked by antagonists, indicating that receptor signaling was not required. Interestingly, the G proteins that these receptors couple to, Galpha(s) and Galpha(q), localized together with their receptors at the plasma membrane and on tubular recycling endosomes. Upon agonist stimulation, Galpha(s) and Galpha(q) remained associated with the PM and these endosomal membranes, whereas beta2 and M3 receptors now entered cells via clathrin-dependent endocytosis. Deletion of the third intracellular loop (i3 loop), which is thought to play a role in agonist-dependent endocytosis of the M3 receptor, had no effect on the constitutive internalization of the receptor. Surprisingly, with agonist, the mutated M3 receptor still internalized and accumulated in cells but through clathrin-independent and not clathrin-dependent endocytosis. These findings demonstrate that GPCRs are versatile PM proteins that can utilize different mechanisms of internalization depending upon ligand activation.

Multiple Residues in the Second Extracellular Loop Are Critical for M3 Muscarinic Acetylcholine Receptor Activation

Recent studies suggest that the second extracellular loop (o2 loop) of bovine rhodopsin and other class I G protein-coupled receptors (GPCRs) targeted by biogenic amine ligands folds deeply into the transmembrane receptor core where the binding of cis-retinal and biogenic amine ligands is known to occur. In the past, the potential role of the o2 loop in agonist-dependent activation of biogenic amine GPCRs has not been studied systematically. To address this issue, we used the M(3) muscarinic acetylcholine receptor (M3R), a prototypic class I GPCR, as a model system. Specifically, we subjected the o2 loop of the M3R to random mutagenesis and subsequently applied a novel yeast genetic screen to identity single amino acid substitutions that interfered with M3R function. This screen led to the recovery of about 20 mutant M3Rs containing single amino acid changes in the o2 loop that were inactive in yeast. In contrast, application of the same strategy to the extracellular N-terminal domain of the M3R did not yield any single point mutations that disrupted M3R function. Pharmacological characterization of many of the recovered mutant M3Rs in mammalian cells, complemented by site-directed mutagenesis studies, indicated that the presence of several o2 loop residues is important for efficient agonist-induced M3R activation. Besides the highly conserved Cys(220) residue, Gln(207), Gly(211), Arg(213), Gly(218), Ile(222), Phe(224), Leu(225), and Pro(228) were found to be of particular functional importance. In general, mutational modification of these residues had little effect on agonist binding affinities. Our findings are therefore consistent with a model in which multiple o2 loop residues are involved in stabilizing the active state of the M3R. Given the high degree of structural homology found among all biogenic amine GPCRs, our findings should be of considerable general relevance.

N-Glycosylation of Fibroblast Growth Factor Receptor 1 Regulates Ligand and Heparan Sulfate Co-receptor Binding

The regulation of cell function by fibroblast growth factors (FGF) occurs through a dual receptor system consisting of a receptor-tyrosine kinase, FGFR and the glycosaminoglycan heparan sulfate (HS). Mutations of some potential N-glycosylation sites in human fgfr lead to phenotypes characteristic of receptor overactivation. To establish how N-glycosylation may affect FGFR function, soluble- and membrane-bound recombinant receptors corresponding to the extracellular ligand binding domain of FGFR1-IIIc were produced in Chinese Hamster Ovary cells. Both forms of FGFR1-IIIc were observed to be heavily N-glycosylated and migrated on SDS-PAGE as a series of multiple bands between 50 and 75 kDa, whereas the deglycosylated receptors migrated at 32 kDa, corresponding to the expected molecular weight of the polypeptides. Optical biosensor and quartz crystal microbalance-dissipation binding assays show that the removal of the N-glycans from FGFR1-IIIc caused an increase in the binding of the receptor to FGF-2 and to heparin-derived oligosaccharides, a proxy for cellular HS. This effect is mediated by N-glycosylation reducing the association rate constant of the receptor for FGF-2 and heparin oligosaccharides. N-Glycans were analyzed by mass spectrometry, which demonstrates a predominance of bi- and tri-antennary core-fucosylated complex type structures carrying one, two, and/or three sialic acids. Modeling of such glycan structures on the receptor protein suggests that at least some may be strategically positioned to interfere with interactions of the receptor with FGF ligand and/or the HS co-receptor. Thus, the N-glycans of the receptor represent an additional pathway for the regulation of the activity of FGFs.

An Interaction Involving an Arginine Residue in the Cytoplasmic Domain of the 5-HT3A Receptor Contributes to Receptor Desensitization Mechanism

A large cytoplasmic domain accounts for approximately one-third of the entire protein of one superfamily of ligand-gated membrane ion channels, which includes nicotinic acetylcholine (nACh), gamma-aminobutyric acid type A (GABA(A)), serotonin type 3 (5-HT3), and glycine receptors. Desensitization is one functional feature shared by these receptors. Because most molecular studies of receptor desensitization have focused on the agonist binding and channel pore domains, relatively little is known about the role of the large cytoplasmic domain (LCD) in this process. To address this issue, we sequentially deleted segments of the LCD of the 5-HT3A receptor and examined the function of the mutant receptors. Deletion of a small segment that contains three amino acid residues (425-427) significantly slowed the desensitization kinetics of the 5-HT3A receptor. Both deletion and point mutation of arginine 427 altered desensitization kinetics in a manner similar to that of the (425-427) deletion without significantly changing the apparent agonist affinity. The extent of receptor desensitization was positively correlated with the polarity of the amino acid residue at 427: the desensitization accelerates with increasing polarity. Whereas the R427L mutation produced the slowest desensitization, it did not significantly alter single channel conductance of 5-HT3A receptor. Thus, the arginine 427 residue in the LCD contributes to 5-HT3A receptor desensitization, possibly through forming an electrostatic interaction with its neighboring residues. Because the polarity of the amino acid residue at 427 is highly conserved, such a desensitization mechanism may occur in other members of the Cys-loop family of ligand-gated ion channels.

Modeling and simulation of stretch blow molding of polyethylene terephthalate

AbstractWhen polyethylene terephthalate (PET) is stretched, it exhibits strain‐hardening properties, which are temperature and strain‐rate dependent. In this paper, two grades of PET are experimentally characterized using biaxial tests. A visco‐hyperelastic model is used to describe the stretching behavior for the polymer. A biaxial characterization method is employed to determine the model parameters using a robust nonlinear curve‐fitting program. This model can represent adequately well the stretching behavior of PET. Based on this model, the membrane finite element formulation is developed to simulate the stretch blow molding process. Two bottles of different designs, produced based on the single‐stage injection blow molding process, are used to validate the model. Good agreement with the bottle thickness profile is observed. Polym. Eng. Sci. 44:1460–1472, 2004. © 2004 Society of Plastics Engineers.

Resolution of two [ 35S]GTP-γ-S binding sites and their response to chronic morphine treatment: A binding surface analysis

The mechanisms by which prolonged exposure to morphine leads to tolerance are not fully understood. We investigated the effects of etorphine (ET) on [ 35S]guanosine 5′-(-thio)-triphosphate ([ 35S]GTP-γ-S) binding in brains of rats made tolerant to morphine via the implantation of morphine (or placebo) pellets. Binding surface analysis was used to characterize the interactions of ET, Gpp(Np)H and GTP-γ-S with sites labeled by [ 35S]GTP-γ-S. Data sets were fitted to one- and two-site binding models using the nonlinear least squares curve fitting program MLAB-PC (Civilized Software, Bethesda, MD, USA). Two binding sites were readily resolved. Chronic morphine significantly increased the B max and K d of the high affinity binding site. ET stimulated [ 35S]GTP-γ-S binding in placebo membranes via an increase in the B max of the high affinity binding site. In contrast, ET stimulated [ 35S]GTP-γ-S in chronic morphine membranes via a large decrease in the K d of the high affinity site. These results suggest that chronic morphine treatment alters the mechanism by which ET stimulates [ 35S]GTP-γ-S binding to G-proteins. Since proper G-protein/receptor coupling increases [ 35S]GTP-γ-S binding via an increase in B max values, these results suggest that opioid receptors in chronic morphine membranes are not normally coupled to G-proteins. These findings corroborate earlier studies that reported changes in G-protein function in morphine tolerant animals.

Pharmacokinetic-pharmacodynamic modeling of risperidone effects on electroencephalography in healthy volunteers.

CNS-active drugs produce specific electroencephalographic changes and the concentration-effect relationship of antipsychotics may be elucidated by adopting electroencephalography (EEG) as an effect measurement tool. The purpose of the present study was to determine the concentration-effect relationship of risperidone by assessing the EEG effect after oral administrations of single dose risperidone in healthy young males. Nine healthy male volunteers received a 1 mg single oral dose of risperidone according to a placebo controlled crossover design. Plasma levels of risperidone and its active metabolite 9-hydroxyrisperidone were measured by radioimmunoassay. Quantitative EEG parameters were obtained for each of four frequency bands through spectral EEG analysis. The difference in the absolute power in the delta frequency band for the F3 lead between risperidone and placebo was used as a drug effect parameter. For pharmacokinetic-pharmacodynamic modeling, the hypothetical effect compartment kinetically linked to plasma by a first-order process was postulated. All curve fittings were done with the non-linear curve-fitting program NONLIN. Our results showed that absolute powers in delta and theta frequency bands were higher for risperidone administration than for placebo at all EEG leads, and the maximum effects were detected at about 3 h after administration of the drug. The hysteresis loop was observed in the plot of plasma concentration of risperidone or sum of risperidone and 9-hydroxyrisperidone (Cp) versus EEG effect for each subject. A linear model adequately described the relationship between the effect compartment concentrations (Ce) and EEG effects, and the two limbs of hysteresis in the Cp-effect plot were collapsed in the Ce-effect plot for risperidone or risperidone plus 9-hydroxyrisperidone. The increases of absolute power for delta and theta frequency bands of EEG were induced by single oral administration of risperidone. The linear PK-PD model fit well with the relationship between effect compartment concentrations (Ce) and EEG effects of risperidone.

Inhibition kinetics of human serum butyrylcholinesterase by Cd 2+, Zn 2+ and Al 3+: comparison of the effects of metal ions on cholinesterases

Butyrylcholinesterase (BChE, EC 3.1.1.8) has been purified about 6600-fold from human serum with a procedure including ammonium sulfate fractionation (55–70%) with acid step at pH 4.5 and procainamide–Sepharose 4B affinity chromatography. The purified enzyme exhibited negative cooperativity with respect to butyrylthiocholine (BTCh) binding at pH 7.5. K S was found to be 0.128±0.012 mM. Inhibition kinetics of the enzyme by Cd 2+, Zn 2+ and Al 3+ were studied in detail. The 1/ v vs 1/[BTCh] plots in the absence (control plot) and in the presence of different concentrations of cations intersected above 1/[BTCh]-axis. The data were analyzed by means of a nonlinear curve fitting program. The results demonstrated that all of the three cations are the linear mixed-type inhibitors of BChE. Ca 2+ and Mg 2+ had no effect on the enzyme activity in the experimental conditions. But when the enzyme was inhibited by 0.5 mM Cd 2+ or Zn 2+, Ca 2+ and Mg 2+ partially reactivated the inhibited allosteric form of BChE. Results were compared with data obtained from brain BChE purified from sheep.

Time domain dielectric spectroscopy: An advanced measuring system

The new time domain measurement system for dielectric measurements is described. The current model is comprised of an IBM PC-AT/486, ‘‘TDM-2,’’ a new time domain measurement system, a set of thermostabilized sample holders, and operation and analysis software. This system is designed for use in the measurement of dielectric parameters of liquid and solid materials over the frequency range 100 kHz–10 GHz. Software consists of programs of registration, accumulation and data collection, Fourier analysis, time domain treatment, analysis software: fast and reliable nonlinear curve fitting programs to determine spectroscopic parameters and correlation analysis in time domain. The system utilizes the difference method of measurement with the registration of primary signals with multiwindow nonuniform sampling. Such a system permits the overlap of a frequency range of five orders in a single measurement.

Surface core-level shifts on Nb(001).

High-resolution 3${\mathit{d}}_{5/2}$ core-level spectra of the clean Nb(001) surface have been obtained at 130 K with 240- and 250-eV synchrotron radiation. The most remarkable result is the positive sign (0.49\ifmmode\pm\else\textpm\fi{}0.01 eV) of the surface core-level shift (the positive sign means that the surface signal is shifted to higher binding energies relative to the bulk one), which is in stark contradiction to the earlier theoretical predictions, but conforms the results from the most recent ab initio calculations. Using a nonlinear curve-fitting program, we have also tentatively obtained the subsurface emission shifted by 0.13\ifmmode\pm\else\textpm\fi{}0.01 eV, a value that is comparable with those for the Ta(001) and W(001) surfaces.

Inhibition Kinetics of Sheep Brain Glutathione Reductase by Cadmium Ion

Glutathione reductase participates in preventing lipid peroxidation by oxygen radicals which results in cellular damage. The brain is among the organs most susceptible to cadmium-induced lipid peroxidation. The mechanism of free radical generation by Cd 2+ is not well understood, but it is known that Cd 2+ is an inhibitor of glutathione reductase. In this study, inhibition kinetics of the brain glutathione reductase by Cd 2+ was investigated. Sheep brain enzyme (11,000-fold purified) was used for this purpose. The data were analyzed by a nonlinear curve fitting program. It was found that the inhibition was competitive with respect to oxidized glutathione and uncompetitive with respect to NADPH. Inhibition constants were found as 12.3 and 9.4 μM, respectively. These findings might contribute to the understanding of the mechanism of lipid peroxidation by Cd 2+ in brain.