Descripción: The adherence of hematite (αFe2O3) particles onto mercury electrodes in water-ethanol mixtures has been studied by counting using optical microscope images. The number of attached particles, when the ethanol content is small, decreases as the ethanol concentration increases. At a mole fraction of ethanol near to 0.2, the number of particles goes through a minimum and then it increases with ethanol concentration. When the electrode potential is modified, curves of the number of particles vs. ethanol mole fraction with the same shape are found, but which cross each other. The dependence on the ethanol concentration can be explained based on the dependence of particle/solution and metal/solution interaction energies with the solvent composition.

Descripción: Lipid-protein interactions play an essential role in the regulation of biological function of integral membrane proteins; however, the underlying molecular mechanisms are not fully understood. Here we explore the modulation by phospholipids of the enzymatic activity of the plasma membrane calcium pump reconstituted in detergent-phospholipid mixed micelles of variable composition. The presence of increasing quantities of phospholipids in the micelles produced a cooperative increase in the ATPase activity of the enzyme. This activation effect was reversible and depended on the phospholipid/detergent ratio and not on the total lipid concentration. Enzyme activation was accompanied by a small structural change at the transmembrane domain reported by 1-aniline-8-naphtalenesulfonate fluorescence. In addition, the composition of the amphipilic environment sensed by the protein was evaluated by measuring the relative affinity of the assayed phospholipid for the transmembrane surface of the protein. The obtained results allow us to postulate a two-stage mechanistic model explaining the modulation of protein activity based on the exchange among non-structural amphiphiles at the hydrophobic transmembrane surface, and a lipid-induced conformational change. The model allowed to obtain a cooperativity coefficient reporting on the efficiency of the transduction step between lipid adsorption and catalytic site activation. This model can be easily applied to other phospholipid/detergent mixtures as well to other membrane proteins. The systematic quantitative evaluation of these systems could contribute to gain insight into the structure-activity relationships between proteins and lipids in biological membranes. © 2012 Dodes Traian et al.

Descripción: Nauplii of the branchiopod crustacean Artemia spp. are widely used as live food in aquaculture. Their nutritional value depends essentially on the fatty acid profile of their lipids, which can be very variable. Study of this variability (often species- and/or ecology-related) proposes interesting theoretical and applied questions. In the present study, cysts (dehydrated dormant eggs) from Argentinean Artemia spp. populations were analysed for their fatty acid profile. Most of the cyst samples analysed (n = 16) were obtained from Artemia persimilis populations, but 3 belonged to A. franciscana. Previous research indicated that A. persimilis populations are confined to inland biotopes, but in this study we report the presence of A. persimilis populations in coastal ecosystems. Cysts from all populations exhibited fatty acid profiles typical of either marine or freshwater, irrespective of the inland or coastal origin of their biotope. This study represents the first time that a significant amount of eicosapentaenoic acid (EPA, 20:5n-3) was detected in A. persimilis cyst samples. We hypothesize on some factors that presumably influence the fatty acid profiles of Artemia spp. cysts: (1) food resources from different habitats, which in turn can be influenced by environmental parameters, (2) the genetic make-up of each population, and/or (3) mechanisms of selective feeding. © Inter-Research 2007.

Descripción: The host-plant environment of phytophagous insects directly affects various aspects of an insect's life cycle. Interestingly, relatively few insect groups have specialized in the exploitation of plants in the Cactaceae family, potentially because of the chemical and ecological challenges imposed by these plants. The cactophilic Drosophila buzzatiiPatterson & Wheeler, 1942 is a well-studied model in evolutionary ecology, partially because of its ability to exploit toxic cactus hosts. Previous studies have shown a negative effect on performance when flies are reared in an alternative columnar cactus host of the genus Trichocereus, relative to its primary cactus host, Opuntia. These observations were attributed to the presence of alkaloids in Trichocereus tissues, a chemical deterrent to herbivores that indirectly affects Drosophila larvae; however, the putative toxic effect of alkaloids has never been tested directly in D. buzzatii. The present study is the first attempt to relate chemical extracts in Trichocereus terscheckii Britton & Rose, 1920 with detrimental effects on D. buzzatii. We assessed the effects of a crude alkaloid extract, rich in phenylethylamines, and a 'non-alkaloid fraction' on viability and adult wing morphology. Our results indicate that rearing larvae on an artificial diet containing different concentrations of the crude alkaloid extract decreased pupal viability and adult size in a concentration-dependent manner. We discuss the role of cactus alkaloids in the evolution of host-plant use in cactophilic flies. © 2013 The Linnean Society of London.

Descripción: The importance of the content of anionic phospholipids [cardiolipin (CL) and phosphatidylglycerol (PG)] in the osmotic adaptation and in the membrane structure of Bacillus subtilis cultures was investigated. Insertion mutations in the three putative cardiolipin synthase genes (ywiE, ywnE and ywjE) were obtained. Only the ywnE mutation resulted in a complete deficiency in cardiolipin and thus corresponds to a true clsA gene. The osmotolerance of a clsA mutant was impaired: although at NaCl concentrations lower than 1.2 M the growth curves were similar to those of its wild-type control, at 1 .5 M NaCl (LBN medium) the lag period increased and the maximal optical density reached was lower. The membrane of the clsA mutant strain showed an increased PG content, at both exponential and stationary phase, but no trace of CL in either LB or LBN medium. As well as the deficiency in CL synthesis, the clsA mutant showed other differences in lipid and fatty acids content compared to the wild-type, suggesting a cross-regulation in membrane lipid pathways, crucial for the maintenance of membrane functionality and integrity. The biophysical characteristics of membranes and large unilamellar vesicles from the wild-type and clsA mutant strains were studied by Laurdan's steady-state fluorescence spectroscopy. At physiological temperature, the clsA mutant showed a decreased lateral lipid packing in the protein-free vesicles and isolated membranes compared with the wild-type strain. Interestingly, the lateral lipid packing of the membranes of both the wild-type and clsA mutant strains increased when they were grown in LBN. In a conditional IPTG-controlled pgsA mutant, unable to synthesize PG and CL in the absence of IPTG, the osmoresistance of the cultures correlated with their content of anionic phospholipids. The transcriptional activity of the clsA and pgsA genes was similar and increased twofold upon entry to stationary phase or under osmotic upshift. Overall, these results support the involvement of the anionic phospholipids in the growth of B. subtilis in media containing elevated NaCl concentrations. © 2006 SGM.

Descripción: Research done in the last years strongly support the hypothesis that PIP aquaporin can form heterooligomeric assemblies, specially combining PIP2 monomers with PIP1 monomers. Nevertheless, the structural elements involved in the ruling of homo versus heterooligomeric organization are not completely elucidated. In this work we unveil some features of monomer-monomer interaction in Beta vulgaris PIP aquaporins. Our results show that while BvPIP2;2 is able to interact with BvPIP1;1, BvPIP2;1 shows no functional interaction. The lack of functional interaction between BvPIP2;1 and BvPIP1;1 was further corroborated by dose-response curves of water permeability due to aquaporin activity exposed to different acidic conditions. We also found that BvPIP2;1 is unable to translocate BvPIP1;1-ECFP from an intracellular position to the plasma membrane when co-expressed, as BvPIP2;2 does. Moreover we postulate that the first extracellular loop (loop A) of BvPIP2;1, could be relevant for the functional interaction with BvPIP1;1. Thus, we investigate BvPIP2;1 loop A at an atomic level by Molecular Dynamics Simulation (MDS) and by direct mutagenesis. We found that, within the tetramer, each loop A presents a dissimilar behavior. Besides, BvPIP2;1 loop A mutants restore functional interaction with BvPIP1;1. This work is a contribution to unravel how PIP2 and PIP1 interact to form functional heterooligomeric assemblies. We postulate that BvPIP2;1 loop A is relevant for the lack of functional interaction with BvPIP1;1 and that the monomer composition of PIP assemblies determines their functional properties. © 2013 Jozefkowicz et al.