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Ionic Environment (ionic + environment)
Selected AbstractsEffects of Ionic Environments on Bovine Serum Albumin Fouling in a Cross-Flow Ultrafiltration SystemCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2007S. Salg Abstract The influence of electrostatic interactions on membrane fouling during the separation of bovine serum albumin (BSA) from solution was studied in a cross-flow ultrafiltration system. Experiments were carried out at different pH values between 3.78 and 7.46; and for different ionic strengths between 0.001,M and 0.1,M. The changes in permeate flux, cake layer resistance, zeta potentials of BSA and polyether sulfone (PES) membranes, and electrostatic interaction energies, were evaluated. At all of the ionic conditions studied, PES membranes are negatively charged. However, BSA molecules are either negatively or positively charged depending on the ionic environment. Whereas the cake layer resistance decreased with increasing pH and ionic strength, the permeate fluxes increased. The calculated electrostatic energy was a minimum at the isoelectric point (IEP) of BSA. However, at this point, the cake resistances corresponding to fouling at each ionic strength, were not minimized. Below the IEP of BSA, the electrostatic forces were attractive, while above the IEP, repulsive electrostatic forces were dominant. [source] The taurine transporter: mechanisms of regulationACTA PHYSIOLOGICA, Issue 1-2 2006X. Han Abstract Taurine transport undergoes an adaptive response to changes in taurine availability. Unlike most amino acids, taurine is not metabolized or incorporated into protein but remains free in the intracellular water. Most amino acids are reabsorbed at rates of 98,99%, but reabsorption of taurine may range from 40% to 99.5%. Factors that influence taurine accumulation include ionic environment, electrochemical charge, and post-translational and transcriptional factors. Among these are protein kinase C (PKC) activation and transactivation or repression by proto-oncogenes such as WT1, c-Jun, c-Myb and p53. Renal adaptive regulation of the taurine transporter (TauT) was studied in vivo and in vitro. Site-directed mutagenesis and the oocyte expression system were used to study post-translational regulation of the TauT by PKC. Reporter genes and Northern and Western blots were used to study transcriptional regulation of the taurine transporter gene (TauT). We demonstrated that (i) the body pool of taurine is controlled through renal adaptive regulation of TauT in response to taurine availability; (ii) ionic environment, electrochemical charge, pH, and developmental ontogeny influence renal taurine accumulation; (iii) the fourth segment of TauT is involved in the gating of taurine across the cell membrane, which is controlled by PKC phosphorylation of serine 322 at the post-translational level; (iv) expression of TauT is repressed by the p53 tumour suppressor gene and is transactivated by proto-oncogenes such as WT1, c-Jun, and c-Myb; and (v) over-expression of TauT protects renal cells from cisplatin-induced nephrotoxicity. [source] Development and evolution of adaptive polyphenismsEVOLUTION AND DEVELOPMENT, Issue 1 2003H. Frederik Nijhout SUMMARY Phenotypic plasticity is the primitive character state for most if not all traits. Insofar as developmental and physiological processes obey the laws of chemistry and physics, they will be sensitive to such environmental variables as temperature, nutrient supply, ionic environment, and the availability of various macro- and micronutrients. Depending on the effect this phenotypic plasticity has on fitness, evolution may proceed to select either for mechanisms that buffer or canalize the phenotype against relevant environmental variation or for a modified plastic response in which some ranges of the phenotypic variation are adaptive to particular environments. Phenotypic plasticity can be continuous, in which case it is called a reaction norm, or discontinuous, in which case it is called a polyphenism. Although the morphological discontinuity of some polyphenisms is produced by discrete developmental switches, most polyphenisms are due to discontinuities in the environment that induce only portions of what is in reality a continuous reaction norm. In insect polyphenisms, the environmental variable that induces the alternative phenotype is a token stimulus that serves as a predictor of, but is not itself, the environment to which the polyphenism is an adaptation. In all cases studied so far, the environmental stimulus alters the endocrine mechanism of metamorphosis by altering either the pattern of hormone secretion or the pattern of hormone sensitivity in different tissues. Such changes in the patterns of endocrine interactions result in the execution of alternative developmental pathways. The spatial and temporal compartmentalization of endocrine interactions has produced a developmental mechanism that enables substantial localized changes in morphology that remain well integrated into the structure and function of the organism. [source] Internalization of tenecin 3 by a fungal cellular process is essential for its fungicidal effect on Candida albicansFEBS JOURNAL, Issue 16 2001Dae-Hee Kim Tenecin 3 is a glycine-rich, antifungal protein of 78 residues isolated from the insect Tenebrio molitor larva. As an initial step towards understanding the antifungal mechanism of tenecin 3, we examined how this protein interacts with the pathogenic fungus Candida albicans to exert its antifungal action. Tenecin 3 did not induce the release of a fluorescent dye trapped in the artificial membrane vesicles and it did not perturb the membrane potential of C. albicans by the initial interaction. Fluorescence confocal microscopy and flow cytometric analysis revealed that tenecin 3 is rapidly internalized into the cytoplasmic space in energy-dependent and temperature-dependent manners. This internalization is also dependent on the ionic environment and cellular metabolic states. These results suggest that the internalization of tenecin 3 into the cytoplasm of C. albicans is mediated by a fungal cellular process. The internalized tenecin 3 is dispersed in the cytoplasm, and the loss of cell viability occurs after this internalization. [source] Global Model for Optimizing Crossflow Microfiltration and Ultrafiltration Processes: A New Predictive and Design ToolBIOTECHNOLOGY PROGRESS, Issue 4 2005Gautam Lal Baruah A global model and algorithm that predicts the performance of crossflow MF and UF process individually or in combination in the laminar flow regime is presented and successfully tested. The model accounts for solute polydispersity, ionic environment, electrostatics, membrane properties and operating conditions. Computer programs were written in Fortran 77 for different versions of the model algorithm that can optimize MF/UF processes rapidly in terms of yield, purity, selectivity, or processing time. The model is validated successfully with three test cases: separation of bovine serum albumin (BSA) from hemoglobin (Hb), capture of immunoglobulin (IgG) from transgenic goat milk by MF, and separation of BSA from IgG by UF. These comparisons demonstrate the capability of the global model to conduct realistic in silico simulations of MF and UF processes. This model and algorithm should prove to be an invaluable technique to rapidly design new or optimize existing MF and UF processes separately or in combination in both pressure-dependent and pressure-independent regimes. [source] Effects of Ionic Environments on Bovine Serum Albumin Fouling in a Cross-Flow Ultrafiltration SystemCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2007S. Salg Abstract The influence of electrostatic interactions on membrane fouling during the separation of bovine serum albumin (BSA) from solution was studied in a cross-flow ultrafiltration system. Experiments were carried out at different pH values between 3.78 and 7.46; and for different ionic strengths between 0.001,M and 0.1,M. The changes in permeate flux, cake layer resistance, zeta potentials of BSA and polyether sulfone (PES) membranes, and electrostatic interaction energies, were evaluated. At all of the ionic conditions studied, PES membranes are negatively charged. However, BSA molecules are either negatively or positively charged depending on the ionic environment. Whereas the cake layer resistance decreased with increasing pH and ionic strength, the permeate fluxes increased. The calculated electrostatic energy was a minimum at the isoelectric point (IEP) of BSA. However, at this point, the cake resistances corresponding to fouling at each ionic strength, were not minimized. Below the IEP of BSA, the electrostatic forces were attractive, while above the IEP, repulsive electrostatic forces were dominant. [source] Functional studies of frataxinACTA PAEDIATRICA, Issue 2004G Isaya Mitochondria generate adenosine triphosphate (ATP) but also dangerous reactive oxygen species (ROS). One-electron reduction of dioxygen in the early stages of the electron transport chain yields a superoxide radical that is detoxified by mitochondrial superoxide dismutase to give hydrogen peroxide. The hydroxyl radical is derived from decomposition of hydrogen peroxide via the Fenton reaction, catalyzed by Fe2+ ions. Mitochondria require a constant supply of Fe2+ for heme and iron-sulfur cluster biosyntheses and therefore are particularly susceptible to ROS attack. Two main antioxidant defenses are known in mitochondria: enzymes that catalytically remove ROS, e.g. superoxide dismutase and glutathione peroxidase, and low molecular weight agents that scavenge ROS, including coenzyme Q, glutathione, and vitamins E and C. An effective defensive system, however, should also involve means to control the availability of pro-oxidants such as Fe2+ ions. There is increasing evidence that this function may be carried out by the mitochondrial protein frataxin. Frataxin deficiency is the primary cause of Friedreich's ataxia (FRDA), an autosomal recessive degenerative disease. Frataxin is a highly conserved mitochondrial protein that plays a critical role in iron homeostasis. Respiratory deficits, abnormal cellular iron distribution and increased oxidative damage are associated with frataxin defects in yeast and mouse models of FRDA. The mechanism by which frataxin regulates iron metabolism is unknown. The yeast frataxin homologue (mYfhlp) is activated by Fe(II) in the presence of oxygen and assembles stepwise into a 48-subunit multimer (,48) that sequesters <2000 atoms of iron in a ferrihydrite mineral core. Assembly of mYfhlp is driven by two sequential iron oxidation reactions: a fast ferroxidase reaction catalyzed by mYfh1p induces the first assembly step (,,3), followed by a slower autoxidation reaction that promotes the assembly of higher order oligomers yielding ,48. Depending on the ionic environment, stepwise assembly is associated with the sequestration of 50,75 Fe(II)/subunit. This Fe(II) is initially loosely bound to mYfh1p and can be readily mobilized by chelators or made available to the mitochondrial enzyme ferrochelatase to synthesize heme. However, as iron oxidation and mineralization proceed, Fe(III) becomes progressively inaccessible and a stable iron-protein complex is produced. In conclusion, by coupling iron oxidation with stepwise assembly, frataxin can successively function as an iron chaperon or an iron store. Reduced iron availability and solubility and increased oxidative damage may therefore explain the pathogenesis of FRDA. [source] | |||||||||||||