A 4.2 kDa synthetic peptide as a potential probe to evaluate the antibacterial activity of coumarin drugs

The coumarin antibiotics are potent inhibitors of DNA replication whose target is the enzyme DNA gyrase, an ATP-dependent bacterial type II topoisomerase. The coumarin drugs inhibit gyrase action by competitive binding to the ATP-binding site of DNA gyrase B protein. The production of new biologically active products has stimulated additional studies on coumarin-gyrase interactions. In this regard, a 4.2 kDa peptide mimic of DNA gyrase B protein from Escherichia coli has been designed and synthesized. The peptide sequence includes the natural fragment 131-146 (coumarin resistance-determining region) and a segment containing the gyrase-DNA interaction region (positions 753-770). The peptide mimic binds to novobiocin (K-a = 1.4 +/- 0.3 x 10(5) m(-1)), plasmid (K-a = 1.6 +/- 0.5 x 10(6) m(-1)) and ATP (K-a = 1.9 f 0.4 x 10(3) m(-1)), results previously found with the intact B protein. on the other hand, the binding to novobiocin was reduced when a mutation of Arg-136 to Leu-136 was introduced, a change previously found in the DNA gyrase B protein from several coumarin-resistant clinical isolates of Escherichia coLi. In contrast, the binding to plasmid and to ATP was not altered. These results suggest that synthetic peptides designed in a similar way to that described here could be used as mimics of DNA gyrase in studies which seek a better understanding of the ATP, as well as coumarin, binding to the gyrase and also the mechanism of action of this class of antibacterial drugs. Copyright (C) 2004 European Peptide Society and John Wiley Sons, Ltd.

Synthesis and thermal study of magnesium complexes with 8-hydroxyquinolinate derivatives

Magnesium ion was reacted with 5,7-dibromo-, 5,7-dichloro-, 7-iodo- and 5-chloro-7-iodo-8-hydroxyquinoline, in acetone/ammonium hydroxide medium under constant stirring to obtain (I) Mg[(C9H4ONBr2)(2)].2H(2)O; (II) Mg[(C9H4ONCl2)(2)].3H(2)O; (III) Mg[(C9H5ONI)(2)].2H(2)O and (IV) Mg[(C9H4ONICl)(2)].2.5H(2)O complexes. The compounds were characterized by elemental analysis, IR spectra, ICP, TG-DTA and DSC.Through thermal decomposition residues were obtained and characterized, by X-ray diffractometry, as a mixture of hexagonal MgBr2 and cubic MgO to the (I) compound at 850degreesC; cubic MgO to the (II), (III) and (IV) compounds at 750, 800 and 700degreesC, respectively.

Wet-chemical synthesis of magnesium niobate nanoparticles powders

Nanosized and highly reactive magnesium mobate (MgNb2O6) powders were successfully synthesized by a new wet-chemical method by means of the dissolution of Nb2O5 center dot 5H(2)O and in a solution of oxalic acid followed by the addition of stoichiometric amounts of magnesium carbonate. The Nb-Mg-oxalic acid solution was evaporated resulting in a dry and amorphous powder that was calcined in the temperature range from 200 to 900 degrees C for 2 h. The crystallization process from the amorphous state to the crystalline MgNb2O6 was followed by thermal analysis. The calcined powders characterized by FT-Raman spectroscopy, X-ray diffraction (XRD) and their morphology examined by high resolution scanning electron microscopy (HR-SEM). Pure MgNb2O6, free from the second phases and obtained at 800 degrees C was confirmed by a combined analysis using XRD and FT-Raman. The average diameter of the particles was calculated from the HR-SEM image as 70 urn approximately. This technique allows a better mixing of the constituent elements and thus a better reactivity of the mixture to obtain pre-reaction products with high purity at lower temperatures and reducing cost. It can offer a great advantage in the PMN-PT formation with respect to the solid-state synthesis. (c) 2006 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

New anti-Alzheimer drugs from biodiversity: the role of the natural acetylcholinesterase inhibitors

Alzheimer's disease (AD) is a progressive neurodegenerative pathology with severe economic and social impact. There is currently no cure, although cholinesterase inhibitors provide effective temporary relief of symptoms in some patients. Nowadays, drug research and development are based on the cholinergic hypothesis that supports the cognition improvement by regulation of the synthesis and release of acetylcholine in the brain. There are only four commercial medicines approved for treatment of AD, and natural products have played an important alternative role in the research for new acetylcholinesterase inhibitors, as exemplified through the discovery of galantamine. This profile conducts us to give in this paper an overview relating the several classes of natural products with anti-cholinesterasic activity as potential templates to the design of new selective and powerful anti-Alzheimer drugs.

Magnesium levels in nutrient solution and common bean (Phaseolus vulgaris L cv Carioca) development. Evaluation of the growth relations and assimilate partitioning

The effect of magnesium levels in nutrient solution upon relation between shoot and root, leaf weight ratio and assimilate partitioning of common bean (Phaseolus vulgaris L. cv Carioca) was studied. Bean plants (3 per pot) were grown in 6 l pots containing Hoagland & Arnon n. 2 solution modified to obtain 2.4, 24.3, 48.6, 72.9 and 97.2 ppm of magnesium. The experimental design was a completely randomized factorial replicated 3 times with 5 levels of magnesium and 5 samplings wich were done forthnightly. Therefore, it may be suggested that the 48.6 ppm of magnesium level proposed by Hoagland & Amen (1950) is the best choice for the common bean, according to the conditions of this experiment. Magnesium concentrations over 48.6 ppm didn't show significant alterations of the evaluated parameters. Nutrient solution with 2.4 ppm of magnesium content provides higher efficiency to the common bean plants during almost all its cycle, except the final of the reproductive phase. These results suggest that magnesium concentration increased to 48.6 ppm, in the cycle final perhaps could increase the productivity.

Effect of PbO excess on the formation of lead magnesium niobate perovskite by the columbite method

The effect of lead excess on the pyrochlore-type formation in Pb(Mg1/3Nb2/3)O-3 (PMN) powders has been investigated. The polymeric precursor method was used in the synthesis of the columbite in association to the partial oxalate method to synthesize the PMN powder samples. Structure refinement of the columbite precursor and PMN powders was carried out using the Rietveld method. The quantitative phase analysis showed that the amount of perovskite phase is not affected by PbO excess, but a great excess drives the pyrochlore-type formation so that 3 wt.% of PbO causes the predominance of Mg-containing pyrochlore phase. Using the refined data obtained from the Rietveld refinement, the compositional fluctuation in the perovskite phase was calculated from Nb/Mg ratio values and Pb occupation factor. Mg inclusion occurs concomitant with Ph one into PMN perovskite phase and this effect is directed by PbO excess during powder synthesis. (C) 2003 Elsevier B.V. All rights reserved.

Effect of magnesium on the properties of LiNbO3 thin films prepared from polymeric precursors

The effect of magnesium addition on the phase formation, microstructure and electric and ferroelectric properties of LiNbO3 thin films prepared through polymeric precursors was analyzed. By X ray diffraction no secondary phase was observed with the increase of magnesium concentration. Comparing to pure LiNbO3, the addition of 0.5 and 1.0 mol% of Mg+2 increased of the dielectric constant, while 2.0 mol% decreased it. It was noticed that the increase in additive concentration decreases the ferroelectric remanent polarization and increases the coercive field.

Effects of the magnesium and chloride ions and shikimate on the structure of shikimate kinase from Mycobacterium tuberculosis

Bacteria, fungi and plants can convert carbohydrate and phosphoenolpyruvate into chorismate, which is the precursor of various aromatic compounds. The seven enzymes of the shikimate pathway are responsible for this conversion. Shikimate kinase (SK) is the fifth enzyme in this pathway and converts shikimate to shikimate-3-phosphate. In this work, the conformational changes that occur on binding of shikimate, magnesium and chloride ions to SK from Mycobacterium tuberculosis (MtSK) are described. It was observed that both ions and shikimate influence the conformation of residues of the active site of MtSK. Magnesium influences the conformation of the shikimate hydroxyl groups and the position of the side chains of some of the residues of the active site. Chloride seems to influence the affinity of ADP and its position in the active site and the opening length of the LID domain. Shikimate binding causes a closing of the LID domain and also seems to influence the crystallographic packing of SK. The results shown here could be useful for understanding the catalytic mechanism of SK and the role of ions in the activity of this protein.