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PubMed1991

Vesicle to micelle transitions of egg phosphatidylcholine liposomes induced by nonionic surfactants, poly(oxyethylene) cetyl ethers.

Vesicle to micelle transitions of sonicated liposomes of egg yolk phosphatidylcholine (EPC) induced by a homologous series of nonionic surfactants, poly(oxyethylene) cetyl ethers [POE(n) cetyl ether], were investigated by using the method of turbidity titrations. The turbidities of the mixed dispersions of sonicated vesicles and surfactant were systematically measured as a function of the surfactant added for a wide range of lipid concentrations (from 0.51 to 6.35 mM EPC). From the titration curves, two threshold points representing onset and complete solubilization of liposomal membranes were determined as a probe for the effect of the length of ethylene oxide (EO) moiety on the phase behavior of ternary system of POE(n) cetyl ethers-EPC-excess water. Patterns of turbidity curves and the surfactant concentrations at two threshold points as well as widths of region between two transitions, where lamellar sheets and mixed micelles may coexist, mainly depended on the length of EO head group. With changing the lengths, solubilization of liposomes and phase diagram showed optimal behavior. That is, in the middle range of EO numbers, it resulted in narrowest coexistence region between onset and complete solubilization. Assuming the equilibrium partitioning model, critical effective molar ratios of surfactant to lipid, Rsat, free surfactant concentrations, Dw, and the partition coefficient of surfactant between bilayer and aqueous phase, K, in surfactant-saturated liposomes were quantitatively determined as a function of EO number. Effective ratios, Rsol, and free surfactant concentration in mixed micelles were also determined. In addition, the effects of CMC and HLB of surfactants on the solubilization of liposome were discussed.

Egg Yolk↗
PubMed1998

Systematic method for determining intravenous drug treatment strategies aiding the humoral immune response.

This paper delineates a systematic method for determining "optimal" intravenous drug delivery strategies for patients having illnesses that primarily evoke a humoral immune response and are treatable by antibiotics. The method derives from a nonlinear, distributed predator-prey model that captures the dominant antigen and antibody interaction. This model is developed from relevant physiology, past predator-prey-type modeling work, available data, and pertinent parameter identification. Embedding this predator-prey model into a larger class of uncertain systems, by a finite dimensional approximation and a transformation to a linear fractional representation, enables the application of robust control based on linear matrix inequality optimization techniques. The optimization problem is solved by minimizing an upper bound on a measure of the total drug delivered subject to patient recovery (stability to healthy equilibrium state). Specifically, the paper addresses the treatment of Haemophilus influenzae through modeling, controller development, and simulations of infected adult patients subjected to typical and proposed intravenous antibiotic treatments. Through simulations the proposed intravenous drug strategy shortens patient recovery time, lowers peak drug concentrations and decreases the total drug administered when compared to standard antibiotic strategies.

AIDS-Related Opportunistic Infections↗
PubMed1991

On the FAD-induced dimerization of apo-lipoamide dehydrogenase from Azotobacter vinelandii and Pseudomonas fluorescens. Kinetics of reconstitution.

The apoenzymes of lipoamide dehydrogenase from pig heart and from Pseudomonas fluorescens were prepared at pH 2.7 and pH 4.0, respectively, using a hydrophobic interaction chromatography procedure recently developed for lipoamide dehydrogenase from Azotobacter vinelandii and other flavoproteins [Van Berkel et al. (1988) Eur. J. Biochem. 178, 197-207]. The apoenzyme from pig heart, having 5% of residual activity, shows an equilibrium between the monomeric and dimeric species. Both the yield and the degree of reconstitution of dimeric holoenzyme is 75% of starting material under optimal conditions. The kinetics of reconstitution of pig heart apoenzyme differ slightly from that obtained with the apoenzyme prepared by acid ammonium sulfate precipitation at pH 1.5 [Kalse, J. F. and Veeger, C. (1968) Biochim. Biophys. Acta 159, 244-256]. The apoenzyme from P. fluorescens is in the monomeric state and shows negligible residual activity. The yield and degree of reconstitution of the dimeric holoenzyme is more than 90% of starting material. Reconstitution of the apoenzymes from A. vinelandii and P. fluorescens involves minimally a two-step sequential process. Initial flavin-binding results in regaining of full dichloroindophenol activity, quenching of tryptophan fluorescence and strong increase of FAD fluorescence polarization. In the second step, dimerization occurs as reflected by regain of lipoamide activity, strongly increased FAD fluorescence and increased hyperchroism of the visible absorption spectrum. The kinetics of FAD-induced dimerization are strongly dependent on the apoenzyme used. At 0 degrees C, the monomeric apoenzyme-FAD complex is either stabilized (P. fluorescens) or only transiently detectable (A. vinelandii). Dimerization of P. fluorescens enzyme is strongly stimulated in the presence of NADH.

Animals↗
PubMed1986

The relationship of individual anaerobic thresholds to total, alactic and lactic oxygen debts after a set treadmill run.

This study investigated the relationship of individual anaerobic thresholds to oxygen debt. Anaerobic threshold speed (VTAM) was determined for 21 male university students using a continuous ramp treadmill protocol. The onset of anaerobiosis was determined by visual inspection of excess CO2 elimination. The following week, all subjects ran at the treadmill speed 3.3 m.sec-1 for 10 minutes (this speed split the group into two halves). Recovery oxygen consumption was monitored after this run. Application of double exponential equations by computer and subsequent integration was used to calculate total, alactic, and lactic oxygen debts. Subjects who ran above their VTAM (group L-VTAM) had significantly (p less than .05) higher total, lactic and alactic debts compared to subjects who ran below their VTAM (group H-VTAM). The total debt demonstrated a significant (p less than .05) negative correlation (r = .77) to VTAM in group L-VTAM. This appears to be due to increasing lactic debt, that was also significantly (p less than .05) negatively correlated (r = -.73) to VTAM. Group H-VTAM did not exhibit this characteristic. This study demonstrates that VTAM, as determined by excess CO2 elimination, is a critical factor in determining oxygen debt and therefore, work above this point (which results in the onset of metabolic acidosis) may limit the optimal running speed for a given distance.

Acid-Base Equilibrium↗
PubMed1997

Escherichia coli diacylglycerol kinase is an evolutionarily optimized membrane enzyme and catalyzes direct phosphoryl transfer.

In this contribution the kinetic mechanism and substrate specificity of Escherichia coli diacylglycerol kinase were examined. Steady state kinetic studies were carried out under mixed micellar conditions using a novel continuous coupled assay system. The kinetic data were consistent with a random equilibrium mechanism, implying that diacylglycerol kinase catalyzes direct phosphoryl transfer from MgATP to diacylglycerol. This was supported by failure to detect an enzyme-phosphate covalent intermediate and by the observation that the bisubstrate analog adenosine 5'-tetraphosphoryl-3-O-(1,2-dihexanoyl)-sn-glycerol inhibits the enzyme (Ki << Km,DAG). While diacylglycerol kinase's kcat/Km is modest compared with the efficiency of many water-soluble enzymes, the enzyme nevertheless appears to be an evolutionarily optimized biocatalyst in the sense that its chemical reaction rate approaches the substrate diffusion-controlled limit. The in vivo rate-limiting step of DAGK's reaction appears to be, in part, the transbilayer diffusion of diacylglycerol from the outer leaflet to the inner leaflet of the cytoplasmic membrane where DAGK's active site is located. DAGK was observed to maintain a high nucleotide substrate specificity, with most of this specificity being expressed in the form of reductions in kcat for ATP analogs.

Adenosine Diphosphate↗
PubMed2004

Optimization of ultrafiltration/diafiltration processes for partially bound impurities.

Ultrafiltration and diafiltration processes are used extensively for removal of a variety of small impurities from biological products. There has, however, been no experimental or theoretical analysis of the effects of impurity- product binding on the rate of impurity removal during these processes. Model calculations were performed to account for the effects of equilibrium binding between a small impurity and a large (retained) product on impurity clearance. Experiments were performed using D-tryptophan and bovine serum albumin as a model system. The results clearly demonstrate that binding interactions can dramatically reduce the rate of small impurity removal, leading to large increases in the required number of diavolumes. The optimal product concentration for performing the diafiltration shifts to lower product concentrations in the presence of strong binding interactions. Approximate analytical expressions for the impurity removal were developed which can provide a guide for the design and optimization of industrial ultrafiltration/diafiltration processes.

Complex Mixtures↗
PubMed2000

Mechanism of phosphorus-carbon bond cleavage by lithium in tertiary phosphines. An optimized synthesis of 1,2-Bis(phenylphosphino)ethane

Conditions influencing the extent of P-C(aryl) vs P-C(alkyl) bond cleavage in the reaction of Ph(2)P(CH(2))(2)PPh(2) with lithium in THF have been investigated. The results complement and elucidate earlier work; they indicate that the mechanism of P-C bond cleavage in tertiary phosphines of this type involves a thermodynamic equilibrium between P-C(aryl) and P-C(alkyl) cleaved radicals and anions, followed by reaction and stabilization of these as lithium salts. The addition of water to the reaction mixture causes a reestablishment of the cleavage equilibrium prior to the formation of the secondary phosphines. A mechanism involving competitive release of leaving groups as the thermodynamically most stable anion or radical has been proposed. The preparation of (R, R)-(+/-)/(R, S)-PhP(H)(CH(2))(2)P(H)Ph by this route has been optimized.

Journal Article↗
PubMedDate not supplied

[Formation of evolutionary approach as an explanatory principle for ecology].

Although the connection of ecology with evolutionary idea and specifically with Darwinism was proclaimed for a long time it seems that Herbert Spencer's approach with its emphasize on natural equilibrium was much more often used as its real theoretical base. Elements of Darwinian approach appeared only in 1920-30s in works of those few researchers who studying the distribution and population dynamics of different species tried to understand general mechanisms providing their continuing existence. Later, in the middle of 1950s the first attempts were undertaken to consider the population life history (primarily the age specific schedule of death and reproduction) as a result of natural selection aimed to maintain the necessary level of fitness. A special attention in these studies that burgeoned in 1980-90s was paid to looking for various trade-offs between particular parameters of life history, e.g., between the survival of juveniles and fecundity of adults. The problem of life history optimization became central for the whole branch of science named "evolutionary ecology". Though traditionally this branch is connected with Darwinism, it is rooted rather in Spencer's ideas on moving equilibrium and deals more with static than dynamic. Disproportionately less attention was paid to the evolution of communities since these formations could be hardly interpreted as units of Darwinian selection. Moreover, the ecologists dealing with biosphere as a unified biogeochemical system began insist on "nondarwinian" nature of its evolution. The author considers this opinion as not sufficiently grounded. Darwin's ideas about unavoidable exponential growth, intrinsic for any population, consequent deficiency of resources, and differential survival and reproduction of individuals are still useful while studying the evolution of living organisms (phylogenetics) or the development of biosphere as a global ecosystem.

Animals↗
PubMed1978

[Growth hormone specific binding sites : characteristics of lactogenic receptors induced by estrogens (author's transl)].

In vitro binding of growth hormone was characterized in rat liver. Microsomal preparations were found more active than membranes purified with an aqueous two-phase polymer system. Binding conducted at 4 degrees C was found optimal after 72 hours of incubation in 5 mM Tris-Maleate buffer pH 6.4 with 25 mM CaCl2. Injecting estrone (25 microgram/100 g B.W.) for one week induced the formation of lactogenic receptors, and increased the specific binding of hGH from 2.8 +/- 1.9 to 22.3 +/- 7.1%. Prolactin and hGH, but not rGH or other pituitary hormones, could displace radioactive hGH. With incubations conducted at 37 degrees C, equilibrium was reached more rapidly but at the cost of a more extensive degradation. The presence of membrane receptors in the medium partly protected the hormone against aggregation and degradation. Scatchard plots were obtained from experiments conducted under optimal conditions and analyzed on computer using a program based on an iterative method. Data indicated that lactogenic receptors possessed a single specific binding site for hGH with a constant (Ka) of 2.18 +/- 0.22 x 10(9) M-1 and a binding capacity of 304 +/- 91 fm/mg proteins.

Animals↗
PubMed2003

Mechanistic insights into the development of optical chloride sensors based on the [9]mercuracarborand-3 ionophore.

Fluorescent sensing microspheres based on perhaps the most selective and practically useful chloride ionophore known, the recently reported [9]mercuracarborand-3 (MC-3), have been prepared and optimized for physiological measurements. In initial work, this ionophore was shown to yield functional optical sensing films in combination with an electrically neutral chromoionophore, ETH 5418. Unfortunately, however, these optodes suffered from unacceptably high levels of sodium interference under physiological conditions. To better understand the sensing mechanism, optical and potentiometric binding experiments were used to characterize the stoichiometry and the complex formation constants for this ionophore. It was found that the preferred stoichiometry is 1:2, rather than 1:1 as assumed earlier. The 1:2 complex is extremely stable (logbeta2 = 13.4), but a relatively strong 1:1 complex also exists (log K1 = 9.9). These characteristics were used to fabricate chloride optodes that make use of the stepwise ion-ionophore decomplexation equilibrium, by adding a calculated amount of lipophilic anion exchanger to the polymer film. Such optodes showed dramatically reduced sodium interference while maintaining the excellent selectivity of the traditional formulation. The optimized composition also shifted the measuring range to physiological conditions, making them useful for the assessment of chloride in undiluted and 10-fold-diluted blood at pH 7.4. After necessary alterations of the particle preparation procedure and sensor formulation, the new insights were used to fabricate mass-produced optical sensing microspheres with characteristics essentially identical to those of the optode sensing films.

Chlorides↗
PubMed1991

Development of a turbidimetric immunoassay for on-line monitoring of proteins in cultivation processes.

An on-line assay for a thermostable pullulanase and antithrombin III (AT III) is described. The assay is based on the formation of aggregates between the protein to be measured and antibodies raised against this protein. Assay automation was achieved by utilizing the flow injection analysis (FIA) principles. The apparatus, a stopped-flow, merging-zone manifold, is described in detail. Since the reaction used in an FIA system does not have to reach equilibrium, it was possible to reduce the time for an assay cycle to 2.5 min. A method for simulating cultivation conditions was developed for assay optimization. Using this method, a detection limit of 1 mg l-1 together with a standard deviation of 1.5 was found. A sandwich ELISA was used as reference assay in the case of AT III and an enzymatic activity assay in the case of pullulanase. Correlation coefficients of 0.988 (AT III) and 0.976 (pullulanase) were determined. The turbidimetric assay was successfully used for pullulanase monitoring during a 240-h cultivation of Clostridium thermosulfurogenes.

Antigen-Antibody Complex↗
PubMed2004

Development of infrared optical sensor for selective detection of tyrosine in biological fluids.

In this paper, a new and simple evanescent wave type of infrared biosensor is described for the selective detection of tyrosine in biological fluids. This sensor is based on the formation of copper complexes between the sensing phase and tyrosine. To demonstrate that this principle was applicable to the selective detection of tyrosine, a proline-modified sensing phase was synthesized on the surface of the internal reflection elements. This sensing phase was saturated with copper ions to allow it to interact with tyrosine units in aqueous solution through the formation of stable proline-Cu2+-tyrosine complexes. Tyrosine exhibits a unique spectral feature in its absorption band at 1515 cm-1. This band significantly differs from those of other amino acids and provides a further method for the discrimination of tyrosine. By investigating the signals from 12 amino acids, only three amino acids, each containing a phenyl group, could be sensed selectively by this sensing phase. Based on the unique absorption of tyrosine located at 1515 cm-1, tyrosine can be selectively detected. To perform quantitative analyses of tyrosine using this sensing phase, a theoretical working equation was developed and correlated with the experimental data. The analytical results indicated that the developed equations do explain and predict the detection behaviors of the proposed sensing scheme. Using the optimal conditions, the regression coefficients for standard curves of tyrosine recorded in the region of concentrations below 600 microM were higher than 0.996 under either equilibrium or non-equilibrium conditions. Detection limit of tyrosine when using this method was ca. 3 microM.

Biosensing Techniques↗
PubMed1991

Reversible mechanosensitive ion pumping as a part of mechanoelectrical transduction.

To explain the ability of some mechanosensitive cells to reverse the process of mechanotransduction and to generate mechanical oscillations and emit sound, a piezo-conformational coupling model (PCC model) is proposed. The model includes a transport protein which changes either its volume (PV-coupling) or its area in the membrane (gamma A-coupling) when undergoing conformational transitions. Such a protein can interact with an oscillating pressure to pump ions and create a transmembrane gradient if the affinities of the protein for ions are different at the two sides of membrane. The frequency and concentration windows for mechanical energy transduction were determined. Under optimal conditions, the efficiency of energy transduction can approach the theoretical maximum of 100%. If the concentration gradient exceeds the static head value (quasi-equilibrium which can be built up and maintained by this transport system), the energy transduction reverses and the transporter becomes a generator of mechanical oscillations at the expense of a concentration gradient. Estimation of thermodynamic parameters of the pump shows that the PV-coupling model would require large pressure oscillations to work while the gamma A-coupling model could work in physiological conditions. The gamma A-coupling mechanism may be used by cells for two purposes. In the reverse mode, it can be a force generator for various applications. In the direct mode, it may serve bioenergetic purposes by harvesting the energy of mechanical oscillations and storing it in the form of a concentration gradient. This pump has an unusual thermodynamic feature: it can distinguish the two components of the electrochemical potential gradient,i.e., the concentration gradient and the electrical potential, the latter serving as a permissive switch to open, or close, the pump when the potential reaches the threshold value.Predictions of the PCC model and its probable involvement in biological mechanotransduction are dicussed.

Biological Transport, Active↗
PubMed2005

Cluster and periodic DFT calculations: the adsorption of atomic nitrogen on M(111) (M = Cu, Ag, Au) surfaces.

First-principle density functional calculations with cluster and slab models have been performed to investigate adsorption and thermally activated atomic nitrogen on M(111) (M = Cu, Ag, Au) surfaces. Optimized results indicate that the basis set of the N atom has a distinct effect on the adsorption energy but an indistinct one on the equilibrium distance. For the N/M(111) adsorption systems studied here, the threefold face centered cubic (fcc) hollow site is found to be the most stable adsorption site. The reason for the fcc site is that the perfected adsorption site has been explained by the density of states (DOS) analysis, that is, that N(2p) has the smallest DOS population near the Fermi level on the fcc site as compared with other adsorption sites. The variations of the adsorption energy as a function of adsorption site are similar and in the following order of N-M(111) binding strengths on a given site: Cu(111) > Ag(111) > Au(111). It is found that the N atom forms essentially an ionic bond for the most stable site. Large contributions between the M(ns) and N(2p) orbitals (n = 4, 5, and 6 for Cu, Ag, and Au, respectively) are found for the cluster model at the B3LYP/LANL2DZ-6-31G(d,p) level and also found in the slab DFT-GGA calculation results, which are the main characteristics of M-N bonds. At last, the dissociation of N2 on Cu(111) and Au(111) has also been obtained in this work, and the results showed that the dissociation of N2 on Cu(111) is more active than that on the Au(111) surface.

Journal Article↗
PubMed2004

On the use of Bennett's acceptance ratio method in multi-canonical-type simulations.

A common strategy for mapping coexistence curves is to employ multi-canonical (MUCA) sampling to simulate along a macrostate path connecting two phases. Central to this approach is the task of accurately calculating the importance weights used in the MUCA procedure, which are needed for both effective sampling and accurate determination of phase boundaries. The purpose of this study is to develop a strategy for determining the importance weights that is built upon Bennett's optimized acceptance ratio method. This approach is shown to be closely related to transition matrix schemes, and is used to compute the vapor-liquid equilibrium of a Lennard-Jones fluid and the liquid-liquid equilibrium of a n-hexane/n-perfluorohexane mixture. For the Lennard-Jones system, the importance weights as a function of the number of particles "N" (at fixed temperature and volume) are obtained by using Bennett's method to estimate free energy differences between N and N+1 particle systems over the desired range of N values. In this application, the method is found to perform slightly better than a related transition matrix scheme. For the n-hexane/n-perfluorohexane liquid mixture, the method is designed to obtain weights as a function of composition (for fixed temperature, pressure, and total number of particles); in this case, the method is found to outperform the Gibbs ensemble approach.

Journal Article↗
PubMed2005

Fully dimensional ab initio description of the structure and energetics of azabenzene-argon complexes.

The structure and energetics of van der Waals complexes of argon with azabenzenes: pyridine, pyrazine, pyrimidine, pyridazine, s-triazine, and s-tetrazine are studied using the second-order Moller-Plesset perturbation theory combined with well-balanced basis sets. The full optimization of the cluster structures and computation of the inter- and intramolecular vibrational frequencies is performed by eliminating the basis set superposition error. The argon equilibrium coordinates are calculated with the accuracy comparable to that reached by standard methods of the structure determination from the spectral data. A simple rule to predict the position of argon with respect to the geometric center of the azabenzene ring is found. The calculated harmonic frequencies of the intermolecular vibrational modes are scaled by the factor of 0.85 to eliminate systematic errors coming from the neglect of anharmonic effects. The scaled frequencies agree with the experimental ones to about 1 cm(-1), except for pyrimidine-argon and tetrazine-argon for which empirical fundamental frequency estimates are problematic. A simple relation connecting the intermolecular bending frequencies and the monomer quadrupole tensor is found. The perturbation of the monomer properties caused by complexation is analyzed. The modification of the monomer structure by the interaction with argon and its influence on the binding energy appears to be negligible in all complexes studied. However, this interaction affects appreciably the intramolecular modes and causes their frequency shifts. As a consequence, the dissociation energy of the complexes increases by about 5 cm(-1).

Journal Article↗
PubMed1995

How to get the best out of r-HuEPO.

Inadequate iron supply is probably the most common and most easily treated cause of sub-optimal response to recombinant human erythropoietin (r-HuEPO). A low ferritin value is a reliable indicator of iron deficiency, provided that patients are in equilibrium (e.g. without infection, bleeding, vitamin or folate deficiency). Normal or high ferritin values do not necessarily preclude iron deficiency. Transferrin saturation is not always a reliable indicator of iron deficiency. The measure which best reflects iron supply to the erythron is the percentage of hypochromic red cells. Iron supplementation should be targeted at keeping serum ferritin > 100 micrograms/l, transferrin saturation > 20%, and hypochromic red cells < 10%. Iron status should be monitored monthly for the first few months after initiation of r-HuEPO, and thereafter at 2-3 month intervals. For haemodialysis patients, who have a very high rate of iron loss, i.v. iron administration is preferable and may also be appropriate for patients on continuous ambulatory haemodialysis (CAPD) and pre-dialysis patients. Recent studies with i.v. iron supplementation have shown no difference between the s.c. and i.v. routes of administration of r-HuEPO. Both the i.v. and the s.c. route are appropriate for patients on haemodialysis, whereas patients on CAPD or pre-dialysis patients should receive s.c. r-HuEPO. The optimum frequency of s.c. administration in the vast majority of patients is 2-3 times weekly. For a small number of patients, once weekly s.c. administration may be suitable. When satisfactory haemoglobin values are reached, the dose of r-HuEPO should be titrated down gradually. It should not be stopped abruptly unless there are life-threatening complications.

Anemia↗
PubMed2001

Multiple current reversal in Brownian ratchets.

We address the problem of stationary transport of overdamped Brownian particles in a one-dimensional spatially periodic potential composed of N hills within one period. We show that in a system driven by both thermal equilibrium fluctuations and symmetric dichotomic fluctuations, a proper manipulation of the barrier heights and slopes of the potential leads to multiple drift velocity reversal. Under optimal conditions, the drift velocity as a function of temperature and intensity of dichotomic fluctuations possesses as many as N extrema of alternating signs. There exist N-1 values of a critical temperature which separate regimes of opposite directions of particle transport.

Journal Article↗