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An extracellular thermostable xylanase from a newly isolated thermophilic Actinomadura sp. strain Cpt20 was purified and characterized. Based on matrix-assisted laser desorption-ionization time-of-flight mass spectrometry analysis, the purified enzyme is a monomer with a molecular mass of 20,110.13 Da. The 19 residue N-terminal sequence of the enzyme showed 84% homology with those of actinomycete endoxylanases. The optimum pH and temperature values for xylanase activity were pH 10 and 80 °C, respectively. This xylanase was stable within a pH range of 5-10 and up to a temperature of 90 °C. It showed high thermostability at 60 °C for 5 days and half-life times at 90 °C and 100 °C were 2 and 1 h, respectively. The xylanase was specific for xylans, showing higher specific activity on soluble oat-spelt xylan followed by beechwood xylan. This enzyme obeyed the Michaelis-Menten kinetics, with the K (m) and k (cat) values being 1.55 mg soluble oat-spelt xylan/ml and 388 min(-1), respectively. While the xylanase from Actinomadura sp. Cpt20 was activated by Mn(2+), Ca(2+), and Cu(2+), it was, strongly inhibited by Hg(2+), Zn(2+), and Ba(2+). These properties make this enzyme a potential candidate for future use in biotechnological applications particularly in the pulp and paper industry.

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Guava (Psidium guajava L.) is a fruit tree largely used in folk medicine in tropical and subtropical areas. This exotic species was introduced in a botanical garden in the northeast of Algeria in the 1950’s. The aim of this study is to estimate, for the first time, the antioxidant and anticholinesterase activities of chloroform, ethyl acetate and n-butanol extracts of P. guajava growing in Algeria. Six antioxidant assays were tested, results showed very important efficiency in free radical scavenging, reducing power and β-carotene bleaching of tested extracts. Values of IC50 or A0.5 of some samples were lower than those of standards. With regard to anticholinesterase activity, the inhibitory of both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) was investigated. The extracts exhibited interesting capacity to inhibit these enzymes with low values of IC50 and even less than that of galanthamine. These activities were correlated with total phenolic content which was more important compared to the one found in extracts from trees growing in tropical and subtropical region. This could be due to resistance and adaptation of P. guajava grown in Algeria. The data obtained suggest the use of bioactive compounds from P. guajava leaves as antioxidant and drugs for symptomatic treatment of Alzheimer disease.

Among the heavy metals most commonly found on land, lead is a strongly represented pollutant in soil and sediments. It is easily absorbed and accumulated in different parts of plants. On the macroscopic scale, lead causes unfavorable effects on plants. First and in the event of excess, it may exert toxicity affecting several stages of germination development in leaf formation and root elongation in the early stages of development. The effect of lead on two varieties of durum wheat Triticum durum cv Gta and Vitron have been analyzed on germination under laboratory conditions. The objective is to determine the influence of lead on (i) germinal parameters and (ii) the stress physiological markers. The experiment was set up in a completely randomized design with 3 replications of 20 seeds per variety, including 4 concentrations of Pb(NO 3 ) 2 (0, 320, 430 and 660 ppm) on the germination. Average ambient temperature was 22°C, the humidity was 32% and photoperiod light/dark was 16/8 h. The obtained results showed a real sensitivity of germination to lead. Indeed, it was noted a total absence of germination of the two varieties in all seeds treated with the highest concentration. The treatment of seeds by the increasing doses of lead decreased the germinative faculty considerably, the content of pigments and disrupted the cellular metabolism, the proteins, the proline and glutathione levels. These results indicated that lead stress caused a decrease in germinal parameters and significant impairment of cell biochemical markers. Such effect was inversely proportional to the doses used. It was also noted that the Gta variety was less sensitive to lead toxicity than Vitron.