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PubMedDate not supplied

Sedative effects and cardiorespiratory influences of intravenous flunitrazepam premedication.

Sedative effects and the influence on cardiorespiratory functions of flunitrazepam, 0.015 mg/kg intravenously, were studied in 13 healthy adult volunteers. Immediately after administration, 12 of the 13 subjects responded when their names were called, while one subject required gentle patting on the shoulder to evoke a response. The scores of EEG and electro-oculogram were decreased. Cardiorespiratory changes were mild and not significant clinically. Anterograde amnesia was remarkable. Equilibrium functions were normal at 180 min postdose. Only one subject complained of pain at injection. It was concluded that intravenous injection of 0.015 mg/kg flunitrazepam was an optimal dose for sedation in healthy adults.

Adult↗

PubMed1994

Equilibrium hormone binding to human estrogen receptors in highly diluted cell extracts is non-cooperative and has a Kd of approximately 10 pM.

It is generally accepted that the Kd for hormone binding to estrogen receptors in extracts ranges between 0.1-1 nM and that binding displays positive cooperativity due to formation of homodimers. After carefully optimizing assay procedures, to diminish ligand depletion phenomena and to fully control recoveries, we find a single class of non-interacting high affinity hormone binding sites with a Kd of approx. 10 pM. Ligand depletion was avoided by decreasing receptor concentrations to 5-8 pM. We were therefore obliged to employ radioiodinated estradiol as a probe as the specific radioactivity of tritiated estradiol was too low to maintain the accuracy of the binding assay. Human estrogen receptor extracted from the MCF7 cell line and recombinantly produced (in yeast) wild-type human receptor have identical equilibrium hormone binding characteristics.

Cell-Free System↗

PubMed1996

Optimal sequencing strategies for surveying molecular genetic diversity.

Two commonly used measures of genetic diversity for intraspecies DNA sequence data are based, respectively, on the number of segregating sites, and on the average number of pairwise nucleotide differences. Expressions are derived for their variance in the presence of intragenic recombination for a panmictic population of fixed size that is at neutral equilibrium at the region sequenced. We show that, in contrast to the slow decrease in variance with increasing sample size, if the recombination rate is nonzero, the asymptotic rate of decrease of variance with increasing sequence length, for fixed sample size, is quite rapid. In particular, it is close to that which would be obtained by sequencing independent chromosome regions. The correlation between measures of diversity from linked regions is also examined. For a given total number of bases sequenced in a particular region, optimal sequencing strategies are derived. These typically involve sequencing relatively few (three to 10) long copies of the region. Under optimal strategies, the variances of the two measures are very similar for most parameter values considered. Results concerning optimal sequencing strategies will be sensitive to gross departures from the underlying assumptions, such as population bottlenecks, selective sweeps, and substantial population substructure.

DNA↗

PubMed1990

Role of alkaline secretion and cell restitution in duodenal mucosal protection.

Duodenal alkaline secretion is a protective mechanism that is sensitive to changes in mucosal blood flow and arterial bicarbonate concentration (i.e. bicarbonate delivery to the mucosa). Alkaline secretion has been shown to prevent or limit damage and to facilitate the repair process once damage has occurred. A rapid restitution of the epithelial integrity has been demonstrated in the duodenum. This repair process is sensitive to alterations in nutrient HCO3- supply. Removal of the necrotic cell layer before repair is complete inhibits the re-establishment of epithelial continuity at low luminal pH. However, under optimal conditions repair is completed within a few hours, even with repeated acid challenge.

Acid-Base Equilibrium↗

PubMed2002

2-Pyridinethiol/2-pyridinethione tautomeric equilibrium. A comparative experimental and computational study.

The gas phase and solvent dependent preference of the tautomerization between 2-pyridinethiol (2SH) and 2-pyridinethione (2S) has been assessed using variable temperature Fourier transform infrared (FTIR) experiments, as well as ab initio and density functional theory computations. No spectroscopic evidence (nu(S)(-)(H) stretch) for 2SH was observed in toluene, C(6)D(6), heptane, or methylene chloride solutions. Although, C(s)() 2SH is 2.61 kcal/mol more stable than C(s)() 2S (CCSD(T)/cc-pVTZ//B3LYP/6-311+G(3df,2p)+ZPE), cyclohexane solvent-field relative energies (IPCM-MP2/6-311+G(3df,2p)) favor 2S by 1.96 kcal/mol. This is in accord with the FTIR observations and in quantitative agreement with the -2.6 kcal/mol solution (toluene or C(6)D(6)) calorimetric enthalpy for the 2S/2SH tautomerization favoring the thione. As the intramolecular transition state for the 2S, 2SH tautomerization (2TS) lies 25 (CBS-Q) to 30 kcal/mol (CCSD/cc-pVTZ) higher in energy than either tautomer, tautomerization probably occurs in the hydrogen bonded dimer. The B3LYP/6-311+G(3df,2p) optimized C(2) 2SH dimer is 10.23 kcal/mol + ZPE higher in energy than the C(2)(h)() 2S dimer and is only 2.95 kcal/mol + ZPE lower in energy than the C(2) 2TS dimer transition state. Dimerization equilibrium measurements (FTIR, C(6)D(6)) over the temperature range 22-63 degrees C agree: K(eq)(298) = 165 +/- 40 M(-)(1), DeltaH = -7.0 +/- 0.7 kcal/mol, and DeltaS = -13.4 +/- 3.0 cal/(mol deg). The difference between experimental and B3LYP/6-311+G(3df,2p) [-34.62 cal/(mol deg)] entropy changes is due to solvent effects. The B3LYP/6-311+G(3df,2p) nucleus independent chemical shifts (NICS) are -8.8 and -3.5 ppm 1 A above the 2SH and 2S ring centers, respectively, and the thiol is aromatic. Although the thione is not aromatic, it is stabilized by the thioamide resonance. In solvent, the large 2S dipole, 2-3 times greater than 2SH, favors the thione tautomer and, in conclusion, 2S is thermodynamically more stable than 2SH in solution.

Journal Article↗

PubMed2005

Optimized RF excitation for anatomical brain imaging of the occipital lobe using the 3D MDEFT sequence and a surface transmit coil.

An RF excitation scheme is presented for anatomical imaging of occipital brain areas at 3T using the 3D modified driven equilibrium Fourier transform (MDEFT) sequence and a transmit-receive surface coil. Surface coils operated in the transmit mode usually display a high B(1) inhomogeneity. This causes variations of the flip angle and impairs fat saturation, resulting in blurring, signal losses, and artifacts due to high scalp intensities. A composite binomial pulse with one spectral component for water selective excitation and one spatial component for B(1) inhomogeneity compensation is presented. It is shown experimentally that the pulse prevents image blurring and reduces the scalp signal considerably. The total pulse duration of only 2.4 ms is compatible with the relatively short repetition times (TRs) required for MDEFT imaging. The method is particularly useful for certain applications in neuroimaging that require technical equipment that is too large for standard coils or should not be exposed to RF fields.

Algorithms↗

PubMed1984

Interdependence of H+, Ca2+, and Pi (or vanadate) sites in sarcoplasmic reticulum ATPase.

The phosphorylation of sarcoplasmic reticulum ATPase with Pi in the absence of Ca2+ was studied by equilibrium and kinetic experimentation. The combination of these measurements was then subjected to analysis without assumptions on the stoichiometry of the reactive sites. The analysis indicates that the species undergoing covalent interaction is the tertiary complex E X Pi X Mg formed by independent interaction of the two ligands with the enzyme. The binding constant of Pi or Mg2+ to either free or partially associated enzyme is approximately equal to 10(2) M-1, and no significant synergistic effect is produced by one ligand on the binding of the other; the equilibrium constant (Keq) for the covalent reaction E X Pi X Mg E-P X Mg is approximately equal to 16, with kphosph = 53 s-1, and khyd = 3-4 s-1 (25 degrees C, pH 6.0, no K+). The phosphorylation reaction of sarcoplasmic reticulum ATPase with Pi is highly H+ dependent. Such a pH dependence involves the affinity of enzyme for different ionization states of Pi, as well as protonation of two protein residues per enzyme unit in order to obtain optimal phosphorylation. The experimental data can then be fitted satisfactorily assuming pK values of 5.7 and 8.5 for the two residues in the nonphosphorylated enzyme (changing to 7.7 for one of the two residues, following phosphorylation) and values of 50.0 and 0.58 for the equilibrium constants of the H2(E X HPO4) in equilibrium with H(E-PO3) + H2O and H(E X HPO4) in equilibrium with E-PO3 + H2O reactions, respectively. In addition to the interdependence of H+ and phosphorylation sites, an interdependence of Ca2+ and phosphorylation sites is revealed by total inhibition of the Pi reaction when two high affinity calcium sites per enzyme unit are occupied by calcium. Conversely, occupancy of the phosphate site by vanadate (a stable transition state analogue of phosphate) inhibits high affinity calcium binding. The known binding competition between the two cations and their opposite effects on the phosphorylation reaction suggest that interdependence of phosphorylation site, H+ sites, and Ca2+ sites is a basic mechanistic feature of enzyme catalysis and cation transport.

Adenosine Triphosphatases↗

PubMed2002

Equilibrium modeling of extractive enzymatic hydrolysis of penicillin G with concomitant 6-aminopenicillanic acid crystallization.

In the present downstream processing of penicillin G, penicillin G is extracted from the fermentation broth with an organic solvent and purified as a potassium salt via a number of back-extraction and crystallization steps. After purification, penicillin G is hydrolyzed to 6-aminopenicillanic acid, a precursor for many semisynthetic beta-lactam antibiotics. We are studying a reduction in the number of pH shifts involved and hence a large reduction in the waste salt production. To this end, the organic penicillin G extract is directly to be added to an aqueous immobilized enzyme suspension reactor and hydrolyzed by extractive catalysis. We found that this conversion can exceed 90% because crystallization of 6-aminopenicillanic acid shifts the equilibrium to the product side. A model was developed for predicting the equilibrium conversion in batch systems containing both a water and a butyl acetate phase, with either potassium or D-p-hydroxyphenylglycine methyl ester as counter-ion of penicillin G. The model incorporates the partitioning equilibrium of the reactants, the enzymatic reaction equilibrium, and the crystallization equilibrium of 6-aminopenicillanic acid. The model predicted the equilibrium conversion of Pen G quite reasonably for different values of pH, initial penicillin G concentration and phase volume ratio. The model can be used as a tool for optimizing the enzymatic hydrolysis.

Acetates↗

PubMed2002

Glucose-to-fructose conversion at high temperatures with xylose (glucose) isomerases from Streptomyces murinus and two hyperthermophilic Thermotoga species.

The conversion of glucose to fructose at elevated temperatures, as catalyzed by soluble and immobilized xylose (glucose) isomerases from the hyperthermophiles Thermotoga maritima (TMGI) and Thermotoga neapolitana 5068 (TNGI) and from the mesophile Streptomyces murinus (SMGI), was examined. At pH 7.0 in the presence of Mg(2+), the temperature optima for the three soluble enzymes were 85 degrees C (SMGI), 95 degrees to 100 degrees C (TNGI), and >100 degrees C (TMGI). Under certain conditions, soluble forms of the three enzymes exhibited an unusual, multiphasic inactivation behavior in which the decay rate slowed considerably after an initial rapid decline. However, the inactivation of the enzymes covalently immobilized to glass beads, monophasic in most cases, was characterized by a first-order decay rate intermediate between those of the initial rapid and slower phases for the soluble enzymes. Enzyme productivities for the three immobilized GIs were determined experimentally in the presence of Mg(2+). The highest productivities measured were 750 and 760 kg fructose per kilogram SMGI at 60 degrees C and 70 degrees C, respectively. The highest productivity for both TMGI and TNGI in the presence of Mg(2+) occurred at 70 degrees C, pH 7.0, with approximately 230 and 200 kg fructose per kilogram enzyme for TNGI and TMGI, respectively. At 80 degrees C and in the presence of Mg(2+), productivities for the three enzymes ranged from 31 to 273. A simple mathematical model, which accounted for thermal effects on kinetics, glucose-fructose equilibrium, and enzyme inactivation, was used to examine the potential for high-fructose corn syrup (HFCS) production at 80 degrees C and above using TNGI and SMGI under optimal conditions, which included the presence of both Co(2+) and Mg(2+). In the presence of both cations, these enzymes showed the potential to catalyze glucose-to-fructose conversion at 80 degrees C with estimated lifetime productivities on the order of 2000 kg fructose per kilogram enzyme, a value competitive with enzymes currently used at 55 degrees to 65 degrees C, but with the additional advantage of higher fructose concentrations. At 90 degrees C, the estimated productivity for SMGI dropped to 200, whereas, for TNGI, lifetime productivities on the order of 1000 were estimated. Assuming that the most favorable biocatalytic and thermostability features of these enzymes can be captured in immobilized form and the chemical lability of substrates and products can be minimized, HFCS production at high temperatures could be used to achieve higher fructose concentrations as well as create alternative processing strategies.

Aldose-Ketose Isomerases↗

PubMedDate not supplied

Characterization of a putative pheromone biosynthesis-activating neuropeptide (PBAN) receptor from the pheromone gland of Heliothis peltigera.

The binding of [(3)H]tyrosyl-PBAN28-33NH(2) to pheromone gland membranes of the moth Heliothis peltigera was investigated. The study describes the development of a pheromone biosynthesis-activating neuropeptide (PBAN) radioreceptor assay and demonstrates the presence of a putative PBAN binding site on the pheromone gland. It also describes synthesis of a radioligand and optimization of binding conditions with respect to membrane preparation, number of gland equivalents, kinetics of ligand binding and composition of the binding solution. Binding was found to be optimal when membranes were freshly prepared from frozen glands, incubated at a concentration of one gland equivalent per reaction tube in the presence of 10 mM HCO(3)(-) ions. Equilibrium of ligand binding was obtained after 20 min. Presence of other components such as NaCl, KCl or SH reagents did not have any effect on binding. Binding was found to be saturable, with a K(d) of 5.73 +/- 1.05 x 10(-6) M and a Bmax of 1.85 +/- 0.22 nmol/mg protein. Binding was effectively displaced by unlabeled PBAN1-33NH(2) and PBAN28-33NuEta(2) with a K(i) of 4.3 +/- 1.1 x 10(-6) M and 4.9 +/- 2.6 x 10(-6) M, respectively.

Animals↗

PubMed1992

Bending moments in lower extremity bones for two standing postures.

The goal of this paper is to study how external gravitational forces stress the lower extremity bones and to ascertain and study how muscle activation compensates for the external load. For these purposes relatively accurate anatomical and biomechanical modelling is necessary. For a comparison of the calculated results to the naturally occurring muscular activity, seven-channel surface EMG activity was recorded. For simplicity a two-dimensional model was developed for the sagittal plane including 19 lower extremity muscles relevant to human standing and walking. In the calculation procedure of muscle forces an optimization procedure is also included. The results give rise to the expected assumption that muscle action is covered by two main requirements: first, to stabilize the joint actively (moment equilibrium) and, second, to compensate efficiently for bending moments produced by gravitational and external forces.

Biomechanical Phenomena↗

PubMed2004

Rational behavioral response and the transmission of STDs.

The susceptible-infected (SI) model is extended by allowing for individual optimal choices of self-protective actions against infection, where agents differ with respect to preferences and costs of self-protection. It is shown that a unique endemic equilibrium prevalence exists when the basic reproductive number of a STD is strictly greater than unity, and that the disease-free equilibrium is the unique steady state equilibrium when the basic reproductive number is less than or equal to one. Unlike in models that take individual behavior as given and fixed, the endemic equilibrium prevalence need not vary monotonically with respect to the basic reproductive number. Specifically, with endogenously determined self-protective behavior, a reduction in the basic reproductive number may in fact increase the endemic equilibrium prevalence. The global stability of the endemic steady state is established for the case of a homogeneous population by showing that, for any non-zero initial disease prevalence, there exists an equilibrium path which converges to the endemic steady state.

Humans↗

PubMed1999

On the evolution of recombination and meiosis.

Theories on the evolution of recombination in regard to its ability to increase mean fitness require a consistent source of negative linkage disequilibrium among loci affecting fitness to show an advantage to recombination. Here we present evidence that, at least theoretically, genetic variation for recombination can spread in very large populations under a strictly multiplicative-fitness, deleterious-allele model. The model uses only Mendelian genetics in a multi-locus context to show that a dominant gene for recombination can spread when rare and resist invasion when common. In non-equilibrium populations driven by Muller's ratchet, the gene increases its probability of fixation by increasing the probability of being associated with the best individuals. This occurs at an optimal level of recombination. Its action results in both an immediate and a long-term advantage to recombination amongst the proto-meiotic organisms modelled. The genetic mechanism lends itself naturally to a model for the evolution of meiosis, where modern-day gametes are seen as derivative of ancient unicellular organisms.

Eukaryotic Cells↗

PubMed2006

Geometries and electronic properties of the neutral and charged rare earth Yb-doped Si(n) (n = 1-6) clusters: a relativistic density functional investigation.

The neutral and charged YbSi(n) (n = 1-6) clusters considering different spin configurations have been systematically investigated by using the relativistic density functional theory with generalized gradient approximation. The total bonding energies, equilibrium geometries, Mulliken populations (MP), Hirshfeld charges (HC), fragmentation energies, and highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps are calculated and discussed. The optimized geometries indicate that the most stable YbSi(n) (n = 1-6) clusters keep basically the analogous frameworks as the low-lying Si(n)(+1) clusters, while the charged species deviate from their neutral counterparts, and that the doped Yb tends to occupy the substitutional site of the neutral and charged YbSi(n) isomers. The relative stabilities are investigated in terms of the calculated fragmentation energies, exhibiting enhanced stabilities for the remarkably stable neutral and charged YbSi2 and YbSi5 clusters. Furthermore, the calculated MP and HC values show that the charges of the neutral and charged YbSi(n) clusters transfer from the Yb atom to Si(n) atoms and the Yb atom acts as an electron donor, and that the f orbitals of the Yb atom in the neutral and charged YbSi(n) clusters behave as core without involvement in chemical bonding. The calculated HOMO-LUMO gaps indicate that the YbSi2 and YbSi4+ clusters have stronger chemical stabilities. Comparisons of the Yb-doped Si(n) (n = 1-6) with available theoretical results of transition-metal-doped silicon clusters are made. The growth pattern is investigated also.

Journal Article↗

PubMed1981

Properties of the Bacillus licheniformis A5 glutamine synthetase purified from cells grown in the presence of ammonia or nitrate.

The glutamine synthetase from Bacillus licheniformis A5 was purified by using a combination of polyethylene glycol precipitation and chromatography on Bio-Gel A 1.5m. The resulting preparation was judged to be homogeneous by the criteria of polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, equilibrium analytical ultracentrifugation, and electron microscopic analysis. The enzyme is a dodecamer with a molecular weight of approximately 616,000, and its subunit molecular weight is 51,000. Under optimal assay conditions (pH 6.6, 37 degrees C) apparent Km values for glutamate, ammonia, and manganese.adenosine 5'-triphosphate (1:1 ratio) were 3.6, 0.4, and 0.9 mM, respectively. Glutamine synthetase activity was inhibited approximately 50% by the addition of 5 mM glutamine, alanine, glycine, serine, alpha-ketoglutarate, carbamyl phosphate, adenosine 5'-diphosphate, or inosine 5'-triphosphate to the standard glutamine synthetase assay system, whereas 5 mM adenosine 5'-monophosphate or pyrophosphate caused approximately 90% inhibition of enzyme activity. Phosphorylribosyl pyrophosphate at 5 mM enhanced activity approximately 60%. We were unable to detect any physical or kinetic differences in the properties of the enzyme when it was purified from cells grown in the presence of ammonia or nitrate as sole nitrogen source. The data indicate that B. licheniformis A5 contains one species of glutamine synthetase whose catalytic activity is not regulated by a covalent modification system.

Amino Acids↗

PubMed2003

Mass-selected resonance-enhanced multiphoton ionisation spectra of laser-desorbed molecules for environmental analysis: 16 representative polycyclic aromatic compounds.

Mass-selected gas-phase UV spectra of laser-desorbed molecules at room temperature have been measured via resonance-enhanced multiphoton ionisation (REMPI) and time-of-flight mass selection. The wavelength range of 260 to 320 nm is optimal for detection of polycyclic aromatic hydrocarbons (PAHs) using REMPI-mass spectrometry. A new laser desorption/laser ionisation source has been used which features a compact size and thermal equilibrium of the desorbed molecules. 16 PAHs have been investigated which have been selected by the US Environmental Protection Agency (EPA). These 16 EPA-PAHs are commonly used world-wide to characterise the PAH-load of environmental samples.

Environmental Monitoring↗

PubMed2000

Heparin and heparan sulfate bind interleukin-10 and modulate its activity.

Glycosaminoglycans (GAG) are a group of negatively charged molecules that have been shown to bind and directly regulate the bioactivity of growth factors and cytokines such as basic fibroblast growth factor, transforming growth factor-beta, IL-7, and interferon-gamma. The ability of GAG to interact with human IL-10 (hIL-10) and the effect of these interactions on its biologic activity were analyzed. It was demonstrated by affinity chromatography that hIL-10 binds strongly to heparin-agarose at physiological pH. Biosensor-based binding kinetic analysis indicated an equilibrium dissociation constant, K(d), of 54 nmol/L for this interaction. Human IL-10 stimulated CD16 and CD64 expression on the monocyte/macrophage population within peripheral blood mononuclear cells, with optimal concentrations between 1 and 10 ng/mL. Soluble heparin, heparan sulfate, chondroitin sulfate, and dermatan sulfate were shown to inhibit the hIL-10-induced expression of CD16 and CD64 in a concentration-dependent manner. Heparin and heparan sulfate were most effective with IC(50) values of 100 to 500 microg/mL. Considerably higher concentrations of dermatan sulfate and chondroitin 4-sulfate were required with an IC(50) of 2,000 to 5,000 microg/mL, whereas chondroitin 6-sulfate was essentially inactive. The antagonistic effect of heparin on hIL-10 activity was shown to be dependent on N-sulfation, inasmuch as de-N-sulfated heparin had little or no inhibitory effect on the IL-10- induced expression of CD16, whereas the effect of de-O-sulfated heparin was comparable to that of unmodified heparin. Furthermore, the inhibition of cell-bound proteoglycan sulfation reduced the hIL-10-mediated expression of CD16 molecules on monocytes/macrophages. Taken together, these findings support the hypothesis that soluble and cell-surface GAG and, in particular, their sulfate groups are important in binding and modulation of hIL-10 activity. (Blood. 2000;96:1879-1888)

Amino Acid Sequence↗

PubMed2003

Dilute liquid crystals used to enhance residual dipolar couplings may alter conformational equilibrium in oligosaccharides.

The solution structures of a trisaccharide and a pentasaccharide containing the Lewis(x) motif were determined by two independent approaches using either dipolar cross-relaxation (NOE) or residual dipolar coupling (RDC) data. For the latter, one-bond 13C[bond](1)H RDC enhanced by two different mineral liquid crystals were used alone. Home-written programs were employed firstly for measuring accurately the coupling constants in the direct dimension of non-decoupled HSQC experiments, secondly for transforming each RDC data set into geometrical restraints. In this second program, the complete molecular structure was expressed in a unique frame where the alignment tensor is diagonal. Assuming that the pyranose rings are rigid, their relative orientation is defined by optimizing the glycosidic torsion angles. For the trisaccharide, a good agreement was observed between the results of both approaches (NOE and RDC). In contrast, for the pentasaccharide, strong discrepancies appeared, which seem to result from interactions between the pentasaccharide and the mesogens, affecting conformational equilibrium. This observation is of importance, as it reveals that using simultaneously NOE and RDC can be hazardous as the former represent 99% of the molecules free in solution, whereas the latter correspond to less than 1% of the structure bound to the mesogen.

Algorithms↗