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PubMed1997

Modeling column regeneration effects on ion-exchange chromatography.

The effect of in-place regeneration on equilibrium and kinetic characteristics of the adsorption of bovine serum albumin to a DEAE-cellulose anion exchanger has been determined. Regeneration with sodium hydroxide and time of exposure showed no effect on equilibrium behavior. Breakthrough curves were measured for protein adsorption on fixed-bed columns and analyzed by a simple model to determine the relevant rate constants for the adsorption process. It was found that forward adsorption rate constant decreased exponentially with the chemical treatment exposure time. The implications of the results on the design and optimization of ion-exchange chromatographic processes are discussed.

Adsorption↗
PubMed2003

Inhibitory potential of Crotalus durissus terrificus venom on measles virus growth.

This paper presents the antiviral activity found in a snake with Crotalus durissus terrificus venom (Cdt), studied by use of microplate inhibition assay, using measles virus (MV). Cdt at concentrations below 100 microg/ml showed no cytotoxicity for Vero cells. This study shows the optimal conditions for cell treatment and infection. Two factors that affect virus binding and infection efficiency were studied: the use of an adsorption step, where infection volume was varied; and the concentration of fetal bovine serum (FBS). The adsorption step, with or without FBS, increased the bound virus percentage, whereas it increased bound virus at equilibrium only in FBS-free until 2.5% FBS. In contrast, the addition of 10% FBS decreased the bound virus percentage. The inhibition of MV replication in Vero cells was observed when Cdt was added either before or during cell infection with virus. Its inhibitory concentration against MV replication was 0.1 until 100 microg/ml, respectively. The anti-MV effect of the Cdt was gradually decreased when it was added before or during infection, and little inhibition was observed when Cdt was added 1 h after infection, suggesting that the MV infection was inhibited at the time of the initial events such as at the moment of adsorption and penetration of the viral cycle. In conclusion, Cdt contains anti-MV effects that may be of potential clinical interest.

Animals↗
PubMed2002

Sulfur polymer solidification/stabilization of elemental mercury waste.

Elemental mercury, contaminated with radionuclides, presents a waste disposal problem throughout the Department of Energy complex. In this paper we describe a new process to immobilize elemental mercury wastes, including those contaminated with radionuclides, in a form that is non-dispersible, will meet EPA leaching criteria, and has low mercury vapor pressure. In this stabilization and solidification process, elemental mercury is combined with an excess of powdered sulfur polymer cement (SPC) and sulfide additives in a mixing vessel and heated to approximately 40 degrees C for several hours, until all of the mercury is converted into mercuric sulfide (HgS). Additional SPC is then added and the temperature of the mixture raised to 135 degrees C, resulting in a molten liquid which is poured into a mold where it cools and solidifies. The final treated waste was characterized by powder X-ray diffraction and found to be a mixture of the hexagonal and orthorhombic forms of mercuric sulfide. The Toxicity Characteristic Leaching Procedure was used to assess mercury releases, which for the optimized process averaged 25.8 microg/l, with some samples being well below the new EPA Universal Treatment Standard of 25 microg/l. Longer term leach tests were also conducted, indicating that the leaching process was dominated by diffusion. Values for the effective diffusion coefficient averaged 7.6x10(-18) cm2/s. Concentrations of mercury vapor from treated waste in equilibrium static headspace tests averaged 0.6 mg/m3.

Diffusion↗
PubMed1998

Microtiter plate-format optode.

Microtiter plate-format optodes could be assembled by casting bulk-response membranes into the standard 96-well polypropylene-based plate or by screen printing them on an optically transparent substrate with 96-well pattern. The compositions of thick optode membranes, especially the ratios of poly(vinyl chloride) (PVC) to plasticizer [bis-(2-ethylhexyl) sebacate (DOS)], were carefully optimized to provide reproducible and rapid response. Adjusting the ratio of PVC to DOS by 1:6, bulk-response membranes containing neutral carrier (4-tert-butyl calix[4]arene tetraacetic acid tetraethyl ester for sodium-selective membrane or valinomycin for potassium-selective membrane) and lipophilic pH indicator (ETH 5294) could exhibit equilibrium response in 5 min. The practical utility of microtiter plate-format optodes has been examined by determining clinically relevant electrolytes in serum samples. It was demonstrated that microtiter plate-format optodes can provide high sample throughput (approximately 100 samples in less than 5 min), analytical performance comparable to that of a potentiometric clinical analyzer, and additional information on electrolytes using the same samples prepared for other colorimetric measurements.

Animals↗
PubMedDate not supplied

Biosorption of heavy metals.

Only within the past decade has the potential of metal biosorption by biomass materials been well established. For economic reasons, of particular interest are abundant biomass types generated as a waste byproduct of large-scale industrial fermentations or certain metal-binding algae found in large quantities in the sea. These biomass types serve as a basis for newly developed metal biosorption processes foreseen particularly as a very competitive means for the detoxification of metal-bearing industrial effluents. The assessment of the metal-binding capacity of some new biosorbents is discussed. Lead and cadmium, for instance, have been effectively removed from very dilute solutions by the dried biomass of some ubiquitous species of brown marine algae such as Ascophyllum and Sargassum, which accumulate more than 30% of biomass dry weight in the metal. Mycelia of the industrial steroid-transforming fungi Rhizopus and Absidia are excellent biosorbents for lead, cadmium, copper, zinc, and uranium and also bind other heavy metals up to 25% of the biomass dry weight. Biosorption isotherm curves, derived from equilibrium batch sorption experiments, are used in the evaluation of metal uptake by different biosorbents. Further studies are focusing on the assessment of biosorbent performance in dynamic continuous-flow sorption systems. In the course of this work, new methodologies are being developed that are aimed at mathematical modeling of biosorption systems and their effective optimization. Elucidation of mechanisms active in metal biosorption is essential for successful exploitation of the phenomenon and for regeneration of biosorbent materials in multiple reuse cycles. The complex nature of biosorbent materials makes this task particularly challenging. Discussion focuses on the composition of marine algae polysaccharide structures, which seem instrumental in metal uptake and binding. The state of the art in the field of biosorption is reviewed in this article, with many references to recent reviews and key individual contributions.

Biomass↗
PubMed1972

Disequilibrium in the malate dehydrogenase reaction in rat liver mitochondria in vivo.

1. When [2-(14)C]pyruvate is injected into rats the C3-position of liver glutamate becomes more heavily labelled than the C2-position, thus establishing that oxaloacetate and fumarate are not in equilibrium in rat liver mitochondria in vivo. The amount of disequilibrium was shown to be simply related to the value that the C3-label/C2-label ratio would have were no label recycled. This ratio, z, was calculated for post-absorptive rats in environmental temperatures of 20 degrees and 30 degrees C from determinations of the distribution of label within glutamate 1, 3 and 10min after intravenous injection of [2-(14)C]pyruvate. The values of z (best estimate and range) were 1.65 (1.60-1.69) in rats at 20 degrees C and 2.43 (2.23-2.63) in rats at 30 degrees C. These values of z imply the following rates of interconversion in mitochondria of fumarate and oxaloacetate (in terms of the oxaloacetate-->citrate flux, R) in rats at 20 degrees C: [Formula: see text] and in rats at 30 degrees C: [Formula: see text] 2. The kinetic parameters of malate dehydrogenase and fumarate hydratase and the intramitochondrial concentrations of NAD(+) and NADH under (as far as could be judged) conditions in vivo were collated. From them and the best estimates of R now available were calculated the rates of interconversion of fumarate, malate and oxaloacetate required to give the found values of z. These rates showed that the fumarate hydratase reaction was nearly in equilibrium, but that the malate dehydrogenase reaction was considerably out of equilibrium. The calculations also led to the following conclusions. 3. In livers of rats at 20 degrees and 30 degrees C mitochondrial malate concentrations were respectively about 5 and 1.5 times mean cellular concentrations. 4. Mitochondrial oxaloacetate concentrations were less than 0.2 of the mean cellular concentrations. They were also only 0.65 and 0.55 of the equilibrium concentrations for the malate dehydrogenase reaction in rats at 20 degrees and 30 degrees C respectively. 5. Malate dehydrogenase activity was low because of the very low oxaloacetate concentrations in the mitochondria and the very small fraction of the enzyme complexed with NAD(+), i.e. in each direction one substrate concentration was very sub-optimal.

Animals↗
PubMed2006

Hunting interactomes of a membrane protein: obtaining the largest set of voltage-dependent anion channel-interacting protein epitopes.

The identification of epitopes involved in protein-protein interactions is essential for understanding protein structure and function. Large scale efforts, although identifying the interactions, did not always yield these epitopes, could not confirm most of the known interactions, and seemed particularly unsuccessful for native intrinsic membrane proteins. We have developed a fluidics-based approach (non-steady-state kinetics) to obtain the broadest set of the epitopes interacting with a given target and applied it to a phage display methodology optimized for membrane proteins. Phages expressing a liver cDNA library were screened against a membrane protein (voltage-dependent anion channel) reconstituted into liposomes and captured on a chip surface. The controlled fluidics was obtained by a surface plasmon resonance (SPR) device that combined the advantages of working with minute reaction volumes and non-equilibrium conditions. We demonstrated selective enrichment of binders and could even select for different binding affinities by fractionation of the selected outputs at various elution times. With voltage-dependent anion channel as bait (a mitochondrial channel critical for cellular metabolism and apoptosis) we found at least 40% of its already reported ligands and independently confirmed 55 novel functional interactions, some of which fully blocked the channel. This highly efficient approach is generally applicable for any protein and could be automated and scaled up even without the use of a SPR device. The epitopes directly identified by this method are useful not only for unraveling interactomes but also for drug design and therapeutics.

Bacteriophages↗
PubMed1988

A mathematical model of the Calvin photosynthesis cycle.

1. A mathematical model is presented for photosynthetic carbohydrate formation in C3 plants under conditions of light and carbon dioxide saturation. The model considers reactions of the Calvin cycle with triose phosphate export and starch production as main output processes, and treats concentrations of NADPH, NAD+, CO2, and H+ as fixed parameters of the system. Using equilibrium approximations for all reaction steps close to equilibrium steady-state and transient-state relationships are derived which may be used for calculation of reaction fluxes and concentrations of the 13 carbohydrate cycle intermediates, glucose 6-phosphate, glucose 1-phosphate, ATP, ADP, and inorganic (ortho)phosphate. 2. Predictions of the model were examined with the assumption that photosynthate export from the chloroplast occurs to a medium containing orthophosphate as the only exchangeable metabolite. The results indicate that the Calvin cycle may operate in a single dynamically stable steady state when the external concentration of orthophosphate does not exceed 1.9 mM. At higher concentrations of the external metabolite, the reaction system exhibits overload breakdown; the excessive rate of photosynthate export deprives the system of cycle intermediates such that the cycle activity progressively approaches zero. 3. Reactant concentrations calculated for the stable steady state that may obtain are in satisfactory agreement with those observed experimentally, and the model accounts with surprising accuracy for experimentally observed effects of external orthophosphate on the steady-state cycle activity and rate of starch production. 4. Control analyses are reported which show that most of the non-equilibrium enzymes in the system have a strong regulatory influence on the steady-state level of all of the cycle intermediates. Substrate concentration control coefficients for cycle enzymes may be positive, such that an increase in activity of an enzyme may raise the steady-state concentration of the substrate is consumes. 5. Under optimal external conditions (0.15-0.5 mM orthophosphate), reaction flux in the Calvin cycle is controlled mainly by ATP synthetase and sedoheptulose bisphosphatase; the cycle activity approaches the maximum velocity that can be supported by the latter enzyme. At lower concentrations of external orthophosphate the cycle activity is controlled almost exclusively by the phosphate translocator.(ABSTRACT TRUNCATED AT 400 WORDS)

Carbohydrates↗
PubMed1988

3H-cyclosporine internalization and secretion by human fetal pancreatic islets.

Human fetal pancreatic islets were isolated from 16- to 20-week-old fetuses by a collagenase technique and cultured 48 hr in RPMI 1640 containing 10% human adult serum and unlabeled 0 to 5 micrograms cyclosporine A (CsA)/ml. Insulin secretory capacity of human fetal islets was expressed as a fractional stimulatory ratio FSR = F2/F1 of the fractional secretion rates during two successive 1 hr static incubations first with 2 mM glucose (F1) to stabilize secretion followed by maximal stimulus, i.e., 25 mM glucose plus 10 mM L-leucine and 10 mM L-arginine (F2). Unlabeled CsA at the above concentrations had no significant effects on the insulin secretory capacity expressed by FSR-values. Studies of net uptake of 3H-CsA by islets cultured for varying periods up to 40 hr and expressed as picomole 3H-CsA per picomole islet insulin content demonstrated that uptake rate was slow and did not reach isotopic equilibrium over the 40 hr of culture. When isolated fetal islets were cultured for 48 hr in the presence of 3H-CsA and varying concentrations of unlabeled CsA it was found during two successive 1 hr static incubations that fetal islets secrete insulin concomitantly with 3H-CsA following maximal stimulus for secretion. An optimal secretory molar ratio of 3H-CsA to insulin of 4.0 +/- 1.3 (n = 7) was found after islets were cultured 48 hr in the presence of a saturating 2.128 micrograms 3H-CsA per milliliter culture medium. In three successive 30-min static incubations of 3H-CsA loaded islets, first with low glucose, followed by high glucose plus L-arginine and L-leucine, and finally with high glucose plus L-arginine and L-leucine and 10 mM theophylline, the proportional fractional secretion rates of insulin and 3H-CsA were of the same magnitude. It is concluded that human fetal pancreatic islets during 48 hr of culture in the presence of pharmacologically relevant concentrations of CsA can internalize the drug, which is compartmentalized and concomitantly secreted with insulin following maximal stimuli. Transplanted human fetal islets utilized as delivering units for CsA could be beneficial for the induction of immunotolerance to allografted fetal islets.

Cells, Cultured↗
PubMedDate not supplied

PARSAFE: computer program for safety assessment and optimization of parenteral nutrition formulations based on chemical speciation analysis.

Instability arising from the formation of precipitates and lipid emulsion aggregates is common in parenteral nutrition formulations due to the concentration- and pH-dependent incompatibility of some of the vital ingredients. Previously, the boundaries between stability and instability could only be established through the use of laborious and expensive empirical methods. The predictive technique with the concept of chemical speciation (based on the analysis of many competitive thermodynamic equilibriums) has been adapted for use with parenteral fluids so that these detrimental events may now be avoided. A comprehensive computer program, PARSAFE ((C) 1991. Sponsors interested in this program should contact D.R.W.) has been developed for this purpose. PARSAFE encompasses chemical-speciation techniques and contains a large data base of commonly used intravenous fluid constituents together with the appropriate thermodynamic equilibrium constants describing their interactions so that stability prediction may be readily achieved in hospital pharmacy laboratories. We review the relevant physical chemistry required for the successful implementation of PARSAFE and outline the audit trails involved in the development of the predictive model.

Algorithms↗
PubMed1999

Identification of optimal strategies for increasing whole arm strength using Karush-Kuhn-Tucker multipliers.

OBJECTIVE: The purpose of this study was to develop a computer model for identifying muscles critical to improving functional upper extremity strength. DESIGN: A three-dimensional biomechanical model of the upper extremity was developed, and the predictions were compared to maximal arm strength data collected from healthy volunteers. BACKGROUND: Although several optimization-based mathematical models of the shoulder have been developed, none have utilized the mathematical properties of the Karush-Kuhn-Tucker multipliers to efficiently estimate the effect of strengthening individual muscles on functional strength of the whole arm. METHODS: A static three-dimensional biomechanical model of the glenohumeral, radio-humeral, ulno-humeral and wrist joints was developed for predicting maximal hand exertion forces. The model was formulated as a linear program. Constraints consisted of moment equilibrium conditions and limits on maximum and minimum allowable muscle forces. Predicted arm strengths were compared to maximal pull strength measurements made on 10 subjects (5 male; 5 female). The task involved pulling toward the mid-sagittal plane of the body with the arm flexed 45 degrees. The Karush-Kuhn-Tucker variables associated with the maximal limits on muscle force were computed to estimate the effect of altering the strength of individual muscles on functional arm strength. RESULTS: Maximum pull strengths were predicted well by the model. Karush-Kuhn-Tucker values ranged from 0 (for muscles not at their upper force limits) to 0.11 for the flexor carpi radialis and pectoralis major muscles. Karush-Kuhn-Tucker multipliers were found to be insensitive to the assumed specific tension of muscle. CONCLUSIONS: Upper extremity strength can be predicted from musculoskeletal geometry and physiology using linear programming. RELEVANCE: Karush-Kuhn-Tucker multipliers associated with the muscle force upper limits give insight into the effect of strengthening individual muscles on whole arm exertion strength. Such an analysis may provide insight into the development of optimal rehabilitation protocols.

Adult↗
PubMed1986

Studies of the renal excretion of the hydroxyl analogue of methionine by the chick.

Athens-Canadian Random Bred adult cockerels and chicks were used to compare the metabolism of the free acid form of the methionine hydroxyl analogue (HMB-FA) to L-methionine (LMET). The first experiment was to determine whether HMB-FA was excreted by the kidneys, thus reducing the amount available for protein synthesis. Fasted adult male chickens were given a single oral dose of HMB-FA or LMET containing a radioactive tracer. Urine was collected and analyzed for the amount of radioactive tracer present; blood samples were subjected to blood gas analyses to assess the physiological status of the bird. It was concluded that LMET was the major methionine analogue excreted from roosters dosed with either HMB-FA or LMET, and that HMB-FA was not excreted by the avian kidney. The second experiment was to determine whether the acid-base status of the diet influences the utilization of HMB-FA. Two levels of dietary LMET or HMB-FA and six levels of dietary base were fed to chicks in a complete 2 X 2 X 6 factorial design for a period of 20 days, after which weight gain and feed consumption were determined. The results indicated that the acid-base status of the diet can play a role in maximizing the gain of chicks fed HMB-FA. Optimal dietary conditions for comparing the efficacy of HMB-FA with LMET and the poor performance of HMB-FA in crystalline amino acid diets are discussed.

Acid-Base Equilibrium↗
PubMed2006

Liposomal drug transport: a molecular perspective from molecular dynamics simulations in lipid bilayers.

Computational methods to predict drug permeability across biomembranes prior to synthesis are increasingly desirable to minimize the investment in drug design and development. Significant progress in molecular dynamics (MD) simulation methodologies applied to lipid bilayer membranes, for example, is making it possible to move beyond characterization of the membranes themselves to explore various thermodynamic and kinetic processes governing membrane binding and transport. Such methods are also likely to be directly applicable to the design and optimization of liposomal delivery systems. MD simulations are particularly valuable in addressing issues that are difficult to explore in laboratory experiments due to the heterogeneity of lipid bilayer membranes at the molecular level. Insights emerging from MD simulations are contributing to an understanding of which regions within bilayers are most and least favored by solutes at equilibrium as the solute structure is varied, local diffusivities of permeants, and the origin of the amplified selectivity to permeant size imposed by lipid bilayer membranes, particularly as changes in composition increase acyl chain ordering.

Biological Transport↗
PubMed1983

A convenient equilibrium separation method for competitive protein-binding assay of corticosterone in rat serum.

Competitive protein-binding assays for corticosterone have typically employed adsorption methods for separation of free and bound ligand. Such methods often impose inconveniently strict limits upon incubation time and temperature, due to the necessity of minimizing the progressive loss of bound ligand to the adsorbent. This paper describes a convenient equilibrium assay method in which a centrifugable ion-exchange medium, DEAE-cellulose, is used to separate the corticosteroid binding globulin of rat serum and ligand bound to it, from free ligand. This method allows great latitude in incubation time and temperature, and is therefore very convenient for processing large numbers of samples. An assay optimized for use over the 50-1000 pg range showed midrange precision averaging 12% c.v., an interassay variation of 15%, and high specificity.

Animals↗
PubMed1999

Dimerization of double-stranded RNA possessing a 3'-overhanging single-stranded end.

A simple system derived from the acceptor stem of tRNA(Ala) is presented which undergoes a pH-dependent dimerization. This is brought about by formation of C+-G-C base triples of the pyrimidine motif type between protonated cytidines of the 3' single-stranded end and regularly paired G-C pairs in the double-helical stem. In addition, an unusual interaction between a protonated adenine and a regular G-C pair is suggested. The equilibrium between monomer and dimer forms can be monitored via NMR spectroscopy and UV melting curve analysis. A dimerization enthalpy of 159 kJ mol(-1) was found at pH 5.0. The system could serve as a model for inter- and intra-molecular association, respectively, of single-stranded and double-helical regions to enable optimal packing of large RNA molecules.

Dimerization↗
PubMed2000

Benazeprilat disposition and effect in dogs revisited with a pharmacokinetic/pharmacodynamic modeling approach.

The pharmacokinetic disposition of benazeprilat, an angiotensin-converting enzyme (ACE) inhibitor (ACEI), was assessed with a nonlinear binding model in dogs. A single oral benazepril dose, a single i.v. benazeprilat dose, or a daily oral dose of benazepril for 14 consecutive days was administered. The activity of benazeprilat was assessed by measuring plasma ACE inhibition with an ex vivo assay. Benazeprilat data were fitted to equations corresponding to a monocompartmental model with a volume equal to the extracellular space ( approximately 0.2 l/kg) in which a fraction of benazeprilat was nonlinearily bound to ACE with both a saturable tissue and nontissue binding. The half-life of benazeprilat elimination determined from this physiologically based model was 39 +/- 6 min. The estimated maximal binding capacity of benazeprilat to ACE was approximately 23.5 nmol/kg, 90% of which was tissular. The estimated equilibrium constant of dissociation (K(d)) of benazeprilat to ACE was 2.7 to 4.5 nM. IC(50) values were one order of magnitude lower than K(d) values (i.e., approximately 0.27 nM). The nonlinear disposition of benazeprilat raised several issues and it was concluded that the benazeprilat concentration profile was only relevant to definition of an optimal dosage regimen if the appropriate kinetic model was used to interpret the plasma data.

Administration, Oral↗
PubMed2004

Biological nutrient removal model No.1 (BNRM1).

This paper presents the results of the work carried out by the CALAGUA Group on Mathematical Modelling of Biological Treatment Processes: the Biological Nutrient Removal Model No.1. This model is based on a new concept for dynamic simulation of wastewater treatment plants: a unique model can be used to design, simulate and optimize the whole plant, as it includes most of the biological and physico-chemical processes taking place in all treatment operations. The physical processes included are: settling and clarification processes (flocculated settling, hindered settling and thickening), volatile fatty acids elutriation and gas-liquid transfer. The chemical interactions included comprise acid-base processes, where equilibrium conditions are assumed. The biological processes included are: organic matter, nitrogen and phosphorus removal; acidogenesis, acetogenesis and methanogenesis. Environmental conditions in each operation unit (aerobic, anoxic or anaerobic) will determine which bacterial groups can grow. Thus, only the model parameters related to bacterial groups able to grow in any of the operation units of a specific WWTP will require calibration. One of the most important advantages of this model is that no additional analysis with respect to ASM2d is required for wastewater characterization. Some applications of this model have also been briefly explained in this paper.

Acid-Base Equilibrium↗
PubMed2003

Optimization of solid phase microextraction analysis for the headspace volatile compounds of parmesan cheese.

Optimum conditions of solid phase microextraction (SPME) analysis of the headspace volatile compounds of Parmesan cheese in airtightly sealed 100-mL bottles were developed. The coefficient of variation of SPME analysis on the headspace volatile compounds of Parmesan cheese was 2%. The reproducibility of SPME was improved by a combination of sampling at -10 degrees C, controlling the sample temperature, and uniform magnetic stirring of samples during equilibrium and isolation steps. The sensitivity of SPME increased by 125% in total peak areas by a combination of 40 min of sonication and 25% (w/v) sodium phosphate solution, compared with that of samples containing deionized water only (P < 0.05). The addition of salt solution or sonication treatment in samples increased the headspace volatile compounds of cheese quantitatively without producing any new volatile compounds.

Cheese↗