Effect of Brefeldin A on the synthesis and transport of cell wall polysaccharides and proteins in pea root seedlings

The in vivo effect of Brefeldin A (BFA) on the synthesis andtransport of cell wall polysaccharides and proteins in the rootsof pea seedlings (Pisum sativum L. cv. Alaska) was investigated.BFA (10µgml^—1 inhibited the synthesis of cell wallmatrix polysaccharides by approximately 43%. Under the sameconditions, cellulose synthesis was inhibited by approximately77%. The percentage of incorporation of L—[U—¹⁴C]leucineand L-[U-14C]proline into cytosolic, membrane and cell wallproteins was only slightly changed in the presence of BFA. Inaddition, the drug did not change the pattern of newly synthesizedproteins in the three fractions as judged by SDS—PAGEfluorography. Double labelling of proteins and cell wall polysaccharidesconfirmed the above reported data. All these results showedthat the synthesis and transport of proteins to the cell wallwas only slightly affected by BFA under similar conditions tothose which brought about a strong inhibition of the synthesisof matrix and cellulosic polysaccharides. BFA had no effecton the activity of membrane-bound and digitonin-solubilizedmannan and glucomannan synthase isolated from the third internodeof pea seedlings. This would exclude an effect of BFA at thelevel of the catalytic site of the synthases. The inhibitionof polysaccharide synthesis by the drug was rapidly eliminatedafter its removal. It is concluded that the effect of BFA onthe biosynthesis of cell wall polysaccharides could be causedby an interaction of the drug with the topological organizationof the synthase complexes in the membranes. This effect wouldprecede the action of the drug at the level of vesicle transportto the walls. Key words: Brefeldin A, cell wall polysaccharides (synthesis and transport), Pisum sativum L, polysaccharide synthases, proteins (synthesis and transport)     

Probing the effect of mutations on cytochrome C stability

Although the tertiary structures of mitochondrial cytochromes c (cyts c) seem to be remarkably similar, there are variations in their amino acid sequences, stability and functional properties. GdnHCl-induced unfolding experiments on engineered yeast and horse cyt c were carried out with the aim to to clarify, at molecular level, some aspects concerning the stability of this class of proteins. The results obtained are discussed in the light of the three-dimensional structures of the two proteins.     

Second generation of alpha-tocopherol analogs-nitric oxide donors: Synthesis, physicochemical, and biological characterization

Synthesis, physicochemical, and biological characterization of a series of alpha-tocopherol mimetics with NO-releasing capacity are reported. The selected NO-donor moieties were nitrooxy and furoxan. All products were tested for their in vitro NO-releasing capacities, vasodilating properties and mammal cytotoxic activities. The lipophilic-hydrophilic balance of all products was also evaluated. A new hybrid furoxan, phenol derivative 17, possesses adequate profile of the studied properties.     

Synthetic chalcones, flavanones, and flavones as antitumoral agents: biological evaluation and structure-activity relationships

A series of synthetic chalcones, flavanones, and flavones has been synthesized and evaluated for antitumor activity against the human kidney carcinoma cells TK-10, human mammary adenocarcinoma cells MCF-7 (estrogen receptor-positive), and human colon adenocarcinoma cells HT-29. The most active series is the chalcone ones with the best results against TK-10 and HT-29 cells. Fourteen out of 53 analyzed compounds resulted very active against at least two of the studied tumoral cells. Alkaline single cell gel electrophoresis, comet assay, was performed as a study of the chromosomal aberrations promoted by the compounds on normal cells. Four active and two inactive chalcones were studied in the comet assay against normal human kidney cells (HK-2). A structure-activity relationship analysis of these compounds was performed and for 4- and 3,4-disubstituted derivatives a quantitative correlation was obtained in the case of anti-HT-29 activity.     

Fluid dynamics of establishing left-right patterning in development

How does the clockwise motion of tens of monocilia drive a leftward flow in the node? And, as the observed flow is leftward, how is the fluid recirculating within the node, as it must, because the node is a closed structure? How does the nodal flow lead to left–right symmetry breaking in the embryo? These questions are within the realm of fluid physics, whose application to the problem of left–right symmetry breaking in vertebrates has led to important advances in the field. Birth Defects Research (Part C) 84:95–101, 2008. © 2008 Wiley‐Liss, Inc.     

Characterization of bis(isoorotato)diaquamagnesium(II) dihydrate: a potentially useful complex for magnesium supplementation.

The synthesis and crystal structure of a new Mg(II) complex of stoichiometry [Mg(isoor)2(H2O)2].2H2O, where isoor is the monoanion of 5-carboxyuracil (isoorotic acid), are reported. The structure, solved by single-crystal X-ray diffractometry, shows that it crystallizes in the triclinic space group P(-1) with Z = 1. The electronic, IR and Raman spectra of the complex are briefly discussed. Its thermal behavior was also investigated by means of thermal gravimetry (TG) and differential thermal analysis (DTA) measurements in an oxygen atmosphere. Dissolution studies support the usefulness of the compound for magnesium supplementation.     

Interactions between Hair Cells Shape Spontaneous Otoacoustic Emissions in a Model of the Tokay Gecko's Cochlea

Background

The hearing of tetrapods including humans is enhanced by an active process that amplifies the mechanical inputs associated with sound, sharpens frequency selectivity, and compresses the range of responsiveness. The most striking manifestation of the active process is spontaneous otoacoustic emission, the unprovoked emergence of sound from an ear. Hair cells, the sensory receptors of the inner ear, are known to provide the energy for such emissions; it is unclear, though, how ensembles of such cells collude to power observable emissions.

Methodology and Principal Findings

We have measured and modeled spontaneous otoacoustic emissions from the ear of the tokay gecko, a convenient experimental subject that produces robust emissions. Using a van der Pol formulation to represent each cluster of hair cells within a tonotopic array, we have examined the factors that influence the cooperative interaction between oscillators.

Conclusions and Significance

A model that includes viscous interactions between adjacent hair cells fails to produce emissions similar to those observed experimentally. In contrast, elastic coupling yields realistic results, especially if the oscillators near the ends of the array are weakened so as to minimize boundary effects. Introducing stochastic irregularity in the strength of oscillators stabilizes peaks in the spectrum of modeled emissions, further increasing the similarity to the responses of actual ears. Finally, and again in agreement with experimental findings, the inclusion of a pure-tone external stimulus repels the spectral peaks of spontaneous emissions. Our results suggest that elastic coupling between oscillators of slightly differing strength explains several properties of the spontaneous otoacoustic emissions in the gecko.