Polynomial algorithms for kernels in comparability, permutation and P 4-free graphs

In this paper, we give three polynomial algorithms which detect a kernel in comparability graphs relatively to an M-orientation, in permutation graphs and in P₄-free graphs with a normal orientation. MSC classification: 05C69, 05C85 Correspondence to: Saoula Youcef     

Variable electrical and thermal conductivity in the theory of generalized thermoelastic diffusion

This paper deals with the problem of a thermoelastic half-space with a permeating substance in contact with the bounding plane in the context of the theory of generalized thermoelastic diffusion with one relaxation time and with variable electrical and thermal conductivity. The bounding surface of the half-space is taken to be traction free and subjected to a time dependent thermal shock. The solution is obtained in the Laplace transform domain by a direct approach. A numerical technique is employed to obtain the solution in the physical domain. It is found that there exist two coupled waves, one of which is elastic and the other is thermal, and a third wave affects diffusion mainly. A comparison is made with the results obtained in a thermoelastic medium with and without diffusion in the following cases : (a) the electrical and thermal conductivities have constant values, (b) the presence of magnetic field and (c) the generalized theory in thermoelasticity.     

Production of Xylooligosaccharides by Immobilized His-tagged Recombinant Xylanase from Penicillium occitanis on Nickel-Chelate Eupergit C

Penicillium occitanis xylanase 2 expressed with a His-tag in Pichia pastoris, termed PoXyn2, was immobilized on nickel-chelate Eupergit C by covalent coupling reaction with a high immobilization yield up to 93.49 %. Characterization of the immobilized PoXyn2 was further evaluated. The optimum pH was not affected by immobilization, but the immobilized PoXyn2 exhibited more acidic and large optimum pH range (pH 2.0–4.0) than that of the free PoXyn2 (pH 3.0). The free PoXyn2 had an optimum temperature of 50 °C, whereas that of the immobilized enzyme was shifted to 65 °C. Immobilization increased both pH stability and thermostability when compared with the free enzyme. Time courses of the xylooligosaccharides (XOS) produced from corncob xylan indicated that the immobilized enzyme tends to use shorter xylan chains and to produce more xylobiose and xylotriose initially. At the end of 24-h reaction, XOS mixture contained a total of 21.3 and 34.2 % (w/w) of xylobiose and xylotriose with immobilized xylanase and free xylanase, respectively. The resulting XOS could be used as a special nutrient for lactic bacteria.     

Synthesis of New Symmetric Disubstituted Dithioether Dithiols

Abstract

The β,β′-dihydroxydithioethers, derived from oxirane, have been converted into dithioethers dithiols in good yields. A colloidal solution of gold nanoparticles (AuNPs) with 5,8-dithiadodecane-3,10-dithiol was prepared and showed a good stability from tight binding offered by the thiol group on the Au surfaces.     

New Thermostable Amylase from <Emphasis Type="Italic">Bacillus cohnii</Emphasis> US147 with a Broad pH Applicability

A new thermophilic bacterial strain identified as Bacillus cohnii US147 was isolated from the southern Tunisian soil. The identification was based on physiological tests and molecular techniques related to the 16S ribosomal ribonucleic acid. The isolated strain produced amylase, which was purified. This amylase had an apparent molecular mass of 30 kDa as estimated by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Amylase US147 showed K _m and V _max values of 0.7 mg/ml and 2.2 U/ml, respectively, with starch as the substrate. The enzyme was active in acid and basic pH and had a maximal activity on starch at pH 9 and 70 °C. The enzyme was stable at pH 9 for 72 h and retained half of its activity after incubation at 70 °C for 150 min. A partially inhibition (15%, 25%, 23%, 20%, and 22%) was obtained with 1 mM SDS, 1 mM NaBO₃, 1 mM H₂O_2, 1 mM Zn⁺², and 5 mM ethylenediamine tetraacetic acid (EDTA), respectively. The amylase recovered its original activity by the addition of 10 mM Ca ²⁺ to the 5 mM EDTA. These properties indicated a possible use of this amylase in starch saccharification, in detergent, and in other industrial applications.     

A Novel α-Amylase from Bacillus mojavensis A21: Purification and Biochemical Characterization

α-Amylase from Bacillus mojavensis A21 (BMA.2) was purified to homogeneity by ultrafiltration, Sephadex G-75 gel filtration and Sepharose mono Q anion exchange chromatography, with a 15.3-fold increase in specific activity and 11% recovery. The molecular weight of the BMA.2 enzyme was estimated to be 58 kDa by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and gel filtration. The optimum temperature and pH were 80?°C and 6.5, respectively. BMA.2 belonged to the EDTA-sensitive α-amylase, but its activity was not stimulated by the presence of Ca²⁺ ions. The major end-products of starch hydrolysis were maltohexaose, maltopentaose and maltotriose. The N-terminal amino acid sequence of the first ten amino acids of the purified α-amylase was ASVNGTLMQY. Compared to sequences of other amylases, the ten amino acid sequence contains Val at position 3, while amylases from Bacillus licheniformis NH1 and Bacillus sp. SG-1 have Leu and Thr at position 3, respectively.     

Exclusive alpha-coupling in the aldol reaction of unsaturated trimethylsilyl esters: an efficient and practical direct synthesis of unsaturated beta-hydroxy acids

The lithium enolates of trimethylsilyl but-3-enoate and 3-methylbut-3-enoate reacted with aldehydes and saturated or aromatic ketones at -70 degrees C to give exclusively the alpha-condensation products in excellent yields. The unsaturated beta-hydroxy acids thus obtained were directly identified, and the usual conversion into their methyl esters with diazomethane was not necessary. Unsaturated ketones underwent Michael reaction through alpha-addition leading to the unsaturated 5-oxo acids.     

The Influence of the Extent of Enzymatic Hydrolysis on Antioxidative Properties and ACE-Inhibitory Activities of Protein Hydrolysates from Goby (Zosterisessor ophiocephalus) Muscle

Antioxidant properties and angiotensin-converting enzyme (ACE) inhibitory activities of protein hydrolysates from goby (Zosterisessor ophiocephalus) muscle, with different degrees of hydrolysis (DH) from 5 to 25 %, prepared by treatment with crude proteases extract from smooth hound intestines, were investigated. Goby protein hydrolysates (GPHs) are rich in Gly and Thr, which accounted for 14.1–15 % and 11.6–13.2 % of the total amino acids, respectively. The antioxidant activities of GPHs were investigated by using several in vitro assay systems. All GPHs exhibited significant metal chelating activity and DPPH free radical-scavenging activity, and inhibited linoleic acid peroxidation. For the ACE-inhibitory activity, as the DH increased, the activity of GPHs increased. The obtained results revealed that antioxidant and ACE-inhibitory activities of GPHs were influenced by the degree of hydrolysis. A medium degree of enzymatic hydrolysis was appropriate to obtain GPHs with good antioxidant activity, while small peptides were essential to obtain high ACE inhibitory activity.     

Synthese d'ethyleniques monofluores

Monofluorinated ethylenic compounds have been prepared by action of potassium tertiobutylate either on2-fluorotosylates or 2-fluorochlorides. In the case of 2-fluorochlorides the action, at higher temperature, of basic salt such as KF in ethylene glycol, may be used to prepare monofluorinated ethylenics compounds.