The 0-1 bidimensional knapsack problem: Toward an efficient high-level primitive tool

Efficient codes exist for exactly solving the 0-1 knapsack problem, which is a common primitive structure in relaxation and decomposition techniques for the solution of general models. We suggest moving to a higher primitive level by using the bidimensional knapsack, which can be used to enhance linear programming or Lagrangean type classical relaxations.With the ultimate aim of providing an exact and efficient solution to the bidimensional knapsack problem, we describe here a heuristic approach based on surrogate duality. In particular, we consider the usefulness of a specific preprocessing phase before a possible enumerative phase.Extensive numerical experiments, based on test problems from the literature as well as randomly generated instances, show that our code compares favorably with the GP procedure developed by Gavish and Pirkul for the multidimensional case.     

Complexing properties of an N,N′-methylated diaza-crown-ether

The nature and stability of some transition and heavy metal cation complexes of an N,N′-methylated diaza-crown-ether have been determined in 0.1 M Et₄NClO₄ aqueous solution by means of pH metric measurements. The results are compared to previous ones concerning the homologous unmethylated ligand.     

PHOTODYNAMIC KILLING OF Dictyostelium discoideum AMOEBAE MEDIATED BY 4',5'-DIIODOFLUORESCEIN ISOTHIOCYANATE DEXTRAN. A STRATEGY FOR THE ISOLATION OF THERMOCONDITIONAL ENDOCYTOSIS MUTANTS

4′, 5′-Diiodofluorescein dextran has been synthesized by iodination of fluorescein dextran and it was used as a sensitizer in photodynamic killing of amoebae of the cellular slime mold Dictyostelium discoideum. Amoebae from axenic strain AX2 incubated in the presence of 4′,5′-diiodofluorescein dextran efficiently internalized the molecule by fluid-phase pinocytosis. Subsequently, illumination of cells showed dose- and time-dependent loss of viability. The tertiary amine, 2,4- diaza[2,2,2]bicyclooctane, significantly decreased phototoxicity, whereas the presence of D₂O increased phototoxicity. These effects were fully consistent with a role for excited-state singlet oxygen generated inside the endosomal compartments in the mechanism of photoinjury. A strategy was developed to enrich for temperature-sensitive Dictyostelium endocytosis mutants in a nitrosoguanidine mutagenized population. Incubation with 4′,5′-diiodofluorescein dextran at 27°C to load endosomal compartments was followed by light treatment to kill parent-type cells selectively. In contrast, mutants unable to internalize the fluid-phase marker would survive the treatment. Six temperature-sensitive clones were selected that grew normally at 21°C but did not grow at 27°C. They all showed markedly decreased fluid-phase pinocytosis capacity at nonpermissive temperature as compared to their activity at 21 °C. These mutant strains should be useful in studies designed to characterize endocytosis mechanisms in Dictyostelium.     

Mebendazole complexes with various cyclodextrins: preparation and physicochemical characterization

Mebendazole is an antihelmintic drug, active against many intestinal parasites. Its systemic efficacy is limited by its poor water solubility. The use of natural or derivatized cyclodextrins permeated to multiply notably its apparent solubility, especially with permethyl β-cyclodextrine (PM β-CD) (multiplied by 4700). The inclusion complex formation between mebendazole and this methylated β-cyclodextrin, was characterized by mass spectrometry, powder X-ray diffractometry and Fourier transform infrared spectroscopy: mebendazole seemed to be included in permethyl β-cyclodextrin by its aromatic rings. To prepare inclusion complex of mebendazole and PMβ-CD by solvent evaporation, acetone may be used and the ratio using lower amount of cyclodextrin (MBZ:CD, 1:2) should be used.     

Cell immersion and cell dipping in microfluidic devices

Combining deflective dielectrophoretic barriers with controlled pressure driven liquid flows in microfluidic devices allows accurate handling of particles such as biological cells in suspensions. Working towards cell-based lab-on-a-chip applications, a platform permitting rapid testing of devices having different dielectrophoretic and fluidic subunits was developed. The performance of such a system is shown in the cases of (A) flooding a small number of immobilised cells with a dye and (B) transient buffer swapping of a large number of cells in flow. The transition times for moving cells from one reagent to the other are below 0.5 s in the case of flow-through cell dipping.     

Relationship between vitamin D status and skin phototype in general adult population

A link between bone mineral density and skin color has been reported recently, and pigmentation has been shown to affect cutaneous vitamin D production. In the present study, we investigated the relationship between phototype, global self-assessed sun exposure, geographical location and vitamin D serum levels in 1191 French adults. When the factors were analyzed separately, individuals with lower phototypes as well as those with lower sun exposure showed significantly lower levels of vitamin D than those with darker phototypes or those with higher sun exposure. However, when factors were analyzed as a whole, the vitamin D status was no longer linked with the phototype, but with sun exposure and geographical location. Since phototypes and global self-assessments of sun exposure were positively linked, our data suggest that lower vitamin D levels in fair-skinned individuals are due to their sun exposure behavior.     

ELECTRON SPIN RESONANCE OF MELANIN FROM HAIR. EFFECTS OF TEMPERATURE, pH AND LIGHT IRRADIATION

Abstract— The variation with temperature, pH and light of the ESR signal of hydrated melanin powders from Japanese black hair has been studied. An explanation of the results is proposed on the basis of quinhydrone type complexes and of acid-base equilibria of melanin and its semiquinone radicals. During exposure to light of wavelengths 254–600 nm, both stable and unstable radicals have been observed. The action spectrum for the formation of stable melanin radicals has been determined.     

Etude comparative des composés TiX2 (X = S,Se, Te). Structures de TiTe2 et TiSeTe

The evolution of crystal-structure and chemical-bond characteristics is studied for the series of isotypical compounds TiX₂, with X = S, Se, Te. The structure determination of TiTe₂ and TiSeTe confirms the existence of an increasing trigonal C_3v distortion of metal sites when the chalcogen electronegativity decreases. The ESCA study shows that this distortion is associated with augmentation of the covalent or metallic character of the bonds. The structural and spectroscopic differences appearing from TiS₂ to TiSe₂ can be interpreted by an orbital delocalization in TiSe₂ and TiTe₂, which would explain the semimetallic behavior of these compounds.     

Purification and characterization of an intracellular β-glucosidase from a Candida sake strain isolated from fruit juices

A yeast strain isolated in the laboratory from fruit juices was studied and classified as Candida sake. The strain produces an intracellular beta-glucosidase when grown with cellobiose as the carbon source. The enzyme was purified by ion-exchange chromatography and gel filtration. The molecular mass of the purified intracellular beta-glucosidase, estimated by gel filtration, was 240 kDa. The tetrameric structure of the beta-glucosidase was determined following treatment of the purified enzyme with sodium dodecyl sulfate. The enzyme exhibited optimum activity at 52 degrees C and pH 4.25 with citrate-phosphate buffer. The enzyme was active against soluble glycosides with the (1-->4)-beta configuration, and from Lineweaver Burk plots, a Km value of 6.9 mmol/L was found for p-nitrophenyl-beta-D-glucopyranoside. The beta-glucosidase was found to be tolerant to glucose inhibition with a Ki value of 0.2 mol/L.     

Improvement of Drosophila acetylcholinesterase stability by elimination of a free cysteine

Background

Acetylcholinesterase is irreversibly inhibited by organophosphate and carbamate insecticides allowing its use for residue detection with biosensors. Drosophila acetylcholinesterase is the most sensitive enzyme known and has been improved by in vitro mutagenesis. However, it is not sufficiently stable for extensive utilization. It is a homodimer in which both subunits contain 8 cysteine residues. Six are involved in conserved intramolecular disulfide bridges and one is involved in an interchain disulfide bridge. The 8^th cysteine is not conserved and is present at position 290 as a free thiol pointing toward the center of the protein.

Results

The free cysteine has been mutated to valine and the resulting protein has been assayed for stability using various denaturing agents: temperature, urea, acetonitrile, freezing, proteases and spontaneous-denaturation at room temperature. It was found that the C290V mutation rendered the protein 1.1 to 2.7 fold more stable depending on the denaturing agent.

Conclusion

It seems that stabilization resulting from the cysteine to valine mutation originates from a decrease of thiol-disulfide interchanges and from an increase in the hydrophobicity of the buried side chain.