[Clinical studies on extracorporeal circulation with increased hemodilution. II. Oxygen utilization with special reference to optimal flow rate].
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Acid-Base Equilibrium↗
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Optimal dialysate concentrations based on kinetic modeling.
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Acid-Base Equilibrium↗
Enhanced apoptotic activity of a structurally optimized form of galectin-1.
Galectin-1 is a homodimeric protein with potent anti-inflammatory properties due to its ability to induce apoptosis in thymocytes and T cells. The galectin-1 subunits are not covalently linked but the monomers are in a dynamic equilibrium with the dimeric form. Since the affinity of the monomers for each other is rather low (in the range of 10(-5)M), the in vivo efficacy of galectin-1 is limited because the equilibrium is shifted towards the inactive monomeric form at lower concentrations. In order to overcome this problem, we designed a covalently linked form of the dimer based on the galectin-1 crystal structure. Here we show that this irreversibly dimeric form of galectin-1 is a potent inducer of apoptosis in murine thymocytes as well as murine mature T cells at concentrations 10-fold lower than wild-type galectin-1. This structurally optimized form of galectin-1 may therefore be a potentially powerful tool to treat chronic inflammatory diseases.
Amino Acid Sequence↗
Equilibria, prudent compromises, and the "waiting" game.
While evaluation of many e-negotiation agents are carried out through empirical studies, this work supplements and complements existing literature by analyzing the problem of designing market-driven agents (MDAs) in terms of equilibrium points and stable strategies. MDAs are negotiation agents designed to make prudent compromises taking into account factors such as time preference, outside option, and rivalry. This work shows that 1) in a given market situation, an MDA negotiates optimally because it makes minimally sufficient concession, and 2) by modeling negotiation of MDAs as a game gamma of incomplete information, it is shown that the strategies adopted by MDAs are stable. In a bilateral negotiation, it is proven that the strategy pair of two MDAs forms a sequential equilibrium for gamma. In a multilateral negotiation, it is shown that the strategy profile of MDAs forms a market equilibrium for gamma.
Algorithms↗
Effects of conformational distributions on sigma profiles in COSMO theories.
The charge density or sigma profile of a solute molecule is an essential component in COSMO (conductor-like screen model) based solvation theories, and its generation depends on the molecular conformation used. The usual procedure is to determine the conformation of an isolated molecule, and assume that this is unchanged when the molecule is placed in solution. In this paper, the conformations of 1-hexanol and 2-methoxy-ethanol in both the liquid and vapor phases obtained from Gibbs ensemble simulation and from an isolated-molecule quantum DFT optimization are used to determine the effect of realistic conformation differences on COSMO-based properties predictions. In particular, the vapor pressure at the normal boiling temperature and the binary mixture VLE (vapor-liquid equilibrium) predictions obtained using different conformations are investigated. The results show that the sigma profile for 1-hexanol varies only slightly using the different conformations, while the sigma profile of 2-methoxy-ethanol shows a significant difference between the liquid and vapor phases. Consequently, the vapor pressure predictions for 1-hexanol are similar regardless of the manner in which the conformation population was obtained, while there is a larger difference for 2-methoxy-ethanol depending on whether the liquid or vapor conformations from simulation or the DFT-optimized structure is used. These differences in predictions are seen to be largely due to differences in the ideal solvation energy term. In mixture VLE calculations involving 1-hexanol, we again see that there is little difference in the phase equilibrium predictions among the different conformations, while for the mixture with 2-methoxy-ethanol, the differences in the sigma profiles lead to a more noticeable, though not significant, difference in the phase equilibrium predictions.
Journal Article↗
Arsenic adsorption onto pillared clays and iron oxides.
Arsenic adsorption was carried out on simple materials such as goethite and amorphous iron hydroxide, and more complex matrices such as clay pillared with titanium(IV), iron(III), and aluminum(III). These matrices were synthesized from a bentonite whose montmorillonitic fraction was pillared according to optimized parameters. These sorbents were characterized by various methods: XRD, FTIR, BET, DTA/TGA, surface acidity, and zetametry. Elimination of arsenite and arsenate as a function of pH was studied. Arsenate elimination was favored at acidic pH, whereas optimal arsenite elimination was obtained at 4<pH<9. For pH values above 10, the pillared clays were damaged and elimination decreased. Equilibrium time and adsorption isotherms were also determined for arsenite and arsenate at each matrix auto-equilibrium pH. Amorphous iron hydroxide had the highest adsorption capacities both towards arsenate and arsenite. Adsorption capacities of goethite and iron- and titanium-pillared clays toward arsenate were similar, but those toward arsenite were different. Desorption experiments from the various matrices were carried out. Iron- and titanium-pillared clays showed a desorption capacity above 95% and around 40% respectively, but no desorption rate could be obtained for iron (hydr)oxides as they were damaged during the process.
Adsorption↗
Fourfold Clusters of Rovibrational Energies in H2Po Studied with an ab Initio Potential Energy Function
We report here an ab initio investigation of the cluster effect (i.e., the formation of four-member groups of nearly degenerate rotation-vibration energy levels at higher J and Ka values) in the H2Po molecule. The potential energy function has been calculated ab initio for a total of 143 molecular geometries by means of the CCSD(T) method, using an averaged relativistic effective potential for Po in conjunction with a newly optimized basis set. The values of the potential energy function obtained cover the region up to around 5000 cm-1 above the equilibrium energy. On the basis of the ab initio potential, the rotation-vibration energies of H2209Po have been calculated with the MORBID (Morse oscillator rigid bender internal dynamics) Hamiltonian and computer program. In particular, we have calculated the rotational energy manifolds for J </= 40 in the vibrational ground state. We find that the formation of fourfold clusters in H2Po is very similar to that in H2Te. Copyright 1997 Academic Press. Copyright 1997Academic Press
Journal Article↗
Breakthrough performance of linear-DNA on ion-exchange membrane columns.
Breakthrough performance of linear-DNA adsorption on ion-exchange membrane columns was theoretically and experimentally investigated using batch and fixed-bed systems. System dispersion curves showed the absence of flow non-idealities in the experimental arrangement. Breakthrough curves were not significantly affected by flow-rate or inlet solution concentration. In the theoretical analysis a model was integrated by the serial coupling of the membrane transport model and the system dispersion model. A transport model that considers finite kinetic rate and column dispersed flow was used in the study. A simplex optimization routine coupled to the solution of the partial differential model equations was employed to estimate the maximum adsorption capacity constant, the equilibrium desorption constant and the forward interaction rate-constant, which are the parameters of the membrane transport model. Through this approach a good prediction of the adsorption phenomena is obtained for inlet concentrations and flow rates greater than 0.2 mg/ml and 0.16 ml/min.
Chromatography, Ion Exchange↗
Activated leukocyte cell adhesion molecule (ALCAM/CD166): signaling at the divide of melanoma cell clustering and cell migration?
Orchestrated modulation of cell adhesion is essential for development and homeostasis in multicellular organisms. It optimizes embedding of the cell in its dynamic environment and facilitates appropriate cell responses and intercellular communication. Chronic disturbance of this delicate equilibrium causes defects in tissue architecture and sometimes cancer. In tumor cell biology, dynamic control of adhesion molecules is important to proceed through the metastatic cascade and to allow cell release from the primary tumor, invasion of the surrounding matrix, intravasation and adhesion to vascular endothelial cells to facilitate extravasation. Intertwined and multiple adhesive interactions rather than individual interactions presumably play critical roles in neoplastic development. Yet, knowledge of the contribution of each individual adhesion molecule is essential to unravel this network of interactions. This review will focus on activated leukocyte cell adhesion molecule (ALCAM/CD166) and its role in human melanoma progression. It is hypothesized that ALCAM may function as a cell surface sensor to register local growth saturation and to regulate cellular signaling and dynamic responses.
Activated-Leukocyte Cell Adhesion Molecule↗
A game-theoretic approach to donor kidney sharing.
Graft survival in renal transplantation is a function, amongst other things, of the degree of histocompatibility lymphocyte-A (HLA) tissue matching achieved between donor and recipient. Yet a donor procured at centre A might match a transplant candidate at centre B and vice versa. This raises the question of whether, and under what circumstances, surgeons will offer and exchange donor kidneys and gain from such trade in terms of graft survival. We analyse the problem in a game-theoretic framework where the choice of strategy 'to offer or not?' is evaluated in the context of the uncertainty of reciprocation by the other player(s) in the game. The equilibrium solution to a number of variations of the game is predicted to be non-cooperation resulting in collectively sub-optimal graft survival rates. Some policy options for improving cooperation are considered including exchange incentives and coercive measures.
Cooperative Behavior↗
Cloud point extraction and simultaneous determination of zirconium and hafnium using ICP-OES.
In the present study a simple versatile separation method using cloud point procedure for extraction of trace levels of zirconium and hafnium is proposed. The extraction of analytes from aqueous samples was performed in the presence of quinalizarine as chelating agent and Triton X-114 as a non-ionic surfactant. After phase separation, the surfactant-rich phase was diluted with 30% (v/v) propanol solution containing 1 mol l(-1) HNO3. Then, the enriched analytes in the surfactant-rich phase were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The different variables affecting the complexation and extraction conditions were optimized. Under the optimum conditions (i.e. 3.4 x 10(-5) mol l(-1) quinalizarine, 0.1% (w/v) Triton X-114, 55 degrees C equilibrium temperature) the calibration graphs were linear in the range of 0.5-1000 mug l(-1) with detection limits (DLs) of 0.26 and 0.31 microg l(-1) for Zr and Hf, respectively. Under the presence of foreign ions no significant interference was observed. The precision (%RSD) for 8 replicate determinations at 200 microg l(-1) of Zr and Hf was better than 2.9% and the enrichment factors were obtained as 38.9 and 35.8 for Zr and Hf, respectively. Finally, the proposed method was successfully utilized for the determination of these cations in water and alloy samples.
Journal Article↗
Common polymorphism in interleukin 6 influences survival of women with ovarian and peritoneal carcinoma.
OBJECTIVES: The IL6 -174 promoter polymorphism impacts serum cytokine levels through transcriptional regulation. The objective of our study was to determine if -174 IL6 genotype influences survival in ovarian cancer. METHODS: The IL6 -174 polymorphism was assessed by direct DNA sequencing in lymphocyte DNA from 160 women with invasive ovarian, or peritoneal cancers. IL6 levels were measured in ascites and plasma in a subset of cases using colorimetric sandwich ELISA procedure. Overall survival was calculated according to the method of Kaplan and Meier. Cox regression analysis was used to evaluate the significance of individual variables in multivariate analysis. Chi-square or Fishers Exact was used to assess the significance of contingency tables. RESULTS: The IL6 -174 genotype frequencies of CC (19%), CG (50%), and GG (31%) were in Hardy-Weinberg equilibrium and were similar to published frequencies in Caucasian controls. There were no associations with IL6 -174 genotype and age, stage or optimal cytoreduction. Stage had a significant impact on survival (p=0.003). The IL6 -174 GG genotype was significantly associated with longer overall survival (median 131 months) compared to CC or CG (median 28 months, p=0.0007). In cox regression analysis using the covariates genotype (p=0.006) and stage (p=0.02), both were independently significant. Furthermore, there was no association found between IL6 levels in ascites or plasma, and genotype, stage, or overall survival. CONCLUSIONS: The IL6 -174 GG genotype has a strong, independent, and favorable impact on survival for women with ovarian, and peritoneal carcinoma.
Adult↗
A rationale for the absolute conservation of Asn70 and Pro71 in mitochondrial cytochromes c suggested by protein engineering.
The absolutely conserved residues Asn70 and Pro71 of mitochondrial cytochrome c have been targeted for protein engineering by semisynthesis. Neither residue has even been implicated in mechanistic schemes, and we reasoned that the conservation of this dipeptide was to fulfill a crucial structural role. Semisynthesis was through condensation by autocatalytic fragment religation of natural fragment 1-65 (H) of the horse protein and synthetic 39-residue peptides containing noncoded amino acids prepared by solid-phase methods. High yields of the purified analogs, homoserine70 and norvaline71 cytochromes c, were obtained. Functional tests revealed minor destabilization of the Hse70-containing structure, with little adverse effect in in vitro assays, but [Nva71] cytochrome c was essentially devoid of activity in these systems. This appeared to be a consequence of a shift, more pronounced than any yet reported, in the conformational equilibrium between the active state III conformer and the inactive, 'alkaline' state IV. The results support our view that this dipeptide is optimal for, and rigidifies, the right-angle bend between two alpha-helices, thus determining the conformation of the 70s loop that terminates in the sixth ligand Met80, and 'forcing' the coordination of iron by thioether sulfur in the presence of the adjacent more avid amine ligands of state IV. Not only is [Nva71] cytochrome c inactive at pH 7, but it also proves to be an extremely potent inhibitor of electron transfer by native state III, thus providing the rationale for the evolutionary conservation of a high pK for the ligand exchange reaction.
Amino Acid Sequence↗
Gas-phase and solution conformations of selected dimeric structural units of heparin.
The molecular structure of four dimeric units (D-E, E-F, F-G, and G-H) of the DEFGH structural unit of heparin, their anionic forms, and their sodium salts have been studied using the B3LYP/6-31+G(d) method. The optimized geometries indicate that the most stable structure of these dimeric units in neutral state is stabilized via "bifurcated" sodium bonds. The equilibrium structure of the biologically active anionic forms of the glycosaminoglycans studied changed considerably in a water solution. The stable-energy conformations around glysosidic bonds found for the individual dimeric species investigated are in agreement with the available experimental structural data for the structurally related heparin-derived oligosaccharides.
Carbohydrate Conformation↗
Theoretical study on the photochemical behavior of 4-(dimethylamino)benzonitrile.
Ab initio calculations have been performed to examine the photochemical behavior of 4-(dimethylamino)benzenzonitrile (DMABN). The conical intersection between S2 and S1 (S2/S1-CIX), where the internal conversion takes place after the main transition of S0-S2 at the equilibrium geometry in S0, is characterized by a dimethylamino-twisted quinoid structure where aromaticity of the benzene ring is lost. The optimized geometry of the charge transfer (CT) state in S1 has a feature similar to that of S2/S1-CIX but is not energetically stabilized so much. Consequently, electronically excited DMABN with CT character relaxes into the most stable locally excited (LE) state in S1 through a recrossing at S2/S1-CIX in gas phase or nonpolar solvent. In polar solvent, in contrast, the equilibration between LE and CT takes place in S1 so that the CT state is more stable because of electrostatic interaction. The excited states of DMABN derivatives have been also examined. On the basis of the present computational results, a new and simple guiding principle of the emission properties is proposed, where conventional twisted intramolecular CT (TICT) and planar intramolecular CT (PICT) models are properly incorporated.
Models, Molecular↗
A new concept of bioartificial liver based on a fluidized bed bioreactor.
Many bioartificial livers have been developed, but most of them suffer from difficulty when being scaled up and from poor efficiency of mass transfer between the plasma and the immobilized hepatocytes. We present a new concept of bioartificial liver based on the fluidized bed motion of hepatocytes entrapped in alginate beads. The bioreactor is designed to offer stable behavior. The maximum fluid perfusion velocity is determined to avoid any bead release from the bioreactor. The fluidized bed height depends on the amount of beads and the velocity employed. Under the optimized operating conditions, the mass transfer between perfusion fluid and beads is very efficient; only 10 min are necessary to reach concentration equilibrium. Hence, this fluidized bed bioartificial liver appears to be a promising tool for a liver support system in the treatment of acute liver failure.
Bioreactors↗
Elastic coupling of integral membrane protein stability to lipid bilayer forces.
It has been traditionally difficult to measure the thermodynamic stability of membrane proteins because fully reversible protocols for complete folding these proteins were not available. Knowledge of the thermodynamic stability of membrane proteins is desirable not only from a fundamental theoretical standpoint, but is also of enormous practical interest for the rational design of membrane proteins and for optimizing conditions for their structure determination by crystallography or NMR. Here, we describe the design of a fully reversible system to study equilibrium folding of the outer membrane protein A from Escherichia coli in lipid bilayers. Folding is shown to be two-state under appropriate conditions permitting data analysis with a classical folding model developed for soluble proteins. The resulting free energy and m value, i.e., a measure of cooperativity, of unfolding are DeltaG(u,H2O)(o)=3.4 kcal/mol and m = 1.1 kcal/mol M(-1), respectively, in a reference bilayer composed of palmitoyl-oleoyl-phosphatidylcholine (C(16:0)C(18:1)PC) and palmitoyloleoyl-phosphatidylglycerol (C(16:0)C(18:1)PG). These values are strong functions of the lipid bilayer environment. By systematic variation of lipid headgroup and chain composition, we show that elastic bilayer forces such as curvature stress and hydrophobic mismatch modulate the free energy and cooperativity of folding of this and perhaps many other membrane proteins.
Bacterial Outer Membrane Proteins↗
A model of physical factors in the structural adaptation of microvascular networks in normotension and hypertension.
Adequate function of the microcirculation is vital to any tissue. To maintain an optimal function, microvascular networks must be able to adapt structurally to changes in the physical environment. Here we present a mathematical network model based on vessel wall mechanics. We assume based on experimental observations that longstanding change in transmural pressure elicits a change in the vascular wall-to-lumen ratio for maintaining circumferential wall stress at a certain level. In addition, experimental observations show that chronic change in fluid shear stress at the vascular wall elicits a persistent change in luminal diameter. On this basis we hypothesize that wall influencing substances released from the endothelium in response to shear stress have a certain optimal level in the vascular wall. Deviation from this level will cause vascular remodeling, i.e. a structural change in luminal diameter, until equilibrium is restored. The model explains several of the key features observed experimentally in the microcirculation in normotension and hypertension. Most importantly, it suggests a scenario where overall network structure and network hemodynamics depend on adaptation to local hemodynamic stimuli in the individual vessel. Simulated results show emanating microvascular networks with properties similar to those observed in vivo. The model points to an altered endothelial function as a key factor in the development of vascular changes characteristic of hypertension.
Adaptation, Physiological↗