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Irreversible Loss (irreversible + loss)
Selected AbstractsThermal denaturation pathway of starch phosphorylase from Corynebacterium callunae: Oxyanion binding provides the glue that efficiently stabilizes the dimer structure of the proteinPROTEIN SCIENCE, Issue 6 2000Richard GrießLer Abstract Starch phosphorylase from Corynebacterium callunae is a dimeric protein in which each mol of 90 kDa subunit contains 1 mol pyridoxal 5,-phosphate as an active-site cofactor. To determine the mechanism by which phosphate or sulfate ions bring about a greater than 500-fold stabilization against irreversible inactivation at elevated temperatures (,50°C), enzyme/oxyanion interactions and their role during thermal denaturation of phosphorylase have been studied. By binding to a protein site distinguishable from the catalytic site with dissociation constants of Ksulfate = 4.5 mM and Kphosphate,16 mM, dianionic oxyanions induce formation of a more compact structure of phosphorylase, manifested by (a) an increase by about 5% in the relative composition of the ,-helical secondary structure, (b) reduced 1H/2H exchange, and (c) protection of a cofactor fluorescence against quenching by iodide. Irreversible loss of enzyme activity is triggered by the release into solution of pyridoxal 5,-phosphate, and results from subsequent intermolecular aggregation driven by hydrophobic interactions between phosphorylase subunits that display a temperature-dependent degree of melting of secondary structure. By specifically increasing the stability of the dimer structure of phosphorylase (probably due to tightened intersubunit contacts), phosphate, and sulfate, this indirectly (1) preserves a functional active site up to, 50°C, and (2) stabilizes the covalent protein cofactor linkage up to , 70°C. The effect on thermostability shows a sigmoidal and saturatable dependence on the concentration of phosphate, with an apparent binding constant at 50°C of , 25 mM. The extra stability conferred by oxyanion-ligand binding to starch phosphorylase is expressed as a dramatic shift of the entire denaturation pathway to a , 20°C higher value on the temperature scale. [source] Application of exergy analysis to various psychrometric processesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2003Bilal A. Qureshi Abstract The relation between work and changes in entropy generation arises from the simultaneous treatment of the first and second laws referred to as exergy (or available energy) analysis. In this paper, we discuss thermodynamic analysis of various psychrometric processes using the concept of exergy. A parametric study of each of the processes is carried out to determine the variation of second-law efficiency as a function of mass flow rate, relative humidity and temperature. Other trends such as variation of temperature with relative humidity are also shown where applicable. Irreversible losses are calculated by applying an exergy balance on each system. In this regard, an engineering equation solver (EES) programme is used, which is unique because it has built-in functions for most thermodynamic and transport properties; removing the need for approximate equations. The concept of total exergy as the sum of thermomechanical and chemical parts is employed in calculating the flow exergies for air and water vapor mixtures. It is shown for some processes investigated that an increase in the relative humidity of the incoming air stream increases second-law efficiency. We notice that a decrease in mass flow rate of fresh air (second incoming stream) in the case of adiabatic mixing decreases the second-law efficiency of the process. Also, it is shown that the mass flow rate (of both water and steam) has almost a linear relationship with relative humidity in the range investigated. Copyright © 2003 John Wiley & Sons, Ltd. [source] Purification, characterization and amino-acid sequence analysis of a thermostable, low molecular mass endo-,-1,4-glucanase from blue mussel, Mytilus edulisFEBS JOURNAL, Issue 16 2000Bingze Xu A cellulase (endo-,-1,4- d -glucanase, EC 3.2.1.4) from blue mussel (Mytilus edulis) was purified to homogeneity using a combination of acid precipitation, heat precipitation, immobilized metal ion affinity chromatography, size-exclusion chromatography and ion-exchange chromatography. Purity was analyzed by SDS/PAGE, IEF and RP-HPLC. The cellulase (endoglucanase) was characterized with regard to enzymatic properties, isoelectric point, molecular mass and amino-acid sequence. It is a single polypeptide chain of 181 amino acids cross-linked with six disulfide bridges. Its molecular mass, as measured by MALDI-MS, is 19 702 Da; a value of 19 710.57 Da was calculated from amino-acid composition. The isoelectric point of the enzyme was estimated by isoelectric focusing in a polyacrylamide gel to a value of 7.6. According to amino-acid composition, the theoretical pI is 7.011. The effect of temperature on the endoglucanase activity, with carboxymethyl cellulose and amorphous cellulose as substrates, respectively, was studied at pH 5.5 and displayed an unusually broad optimum activity temperature range between 30 and 50 °C. Another unusual feature is that the enzyme retains 55,60% of its maximum activity at 0 °C. The enzyme readily degrades amorphous cellulose and carboxymethyl cellulose but displays no hydrolytic activity towards crystalline cellulose (Avicel) and shows no cross-specificity for xylan; there is no binding to Avicel. The enzyme can withstand 10 min at 100 °C without irreversible loss of enzymatic activity. Amino-acid sequence-based classification has revealed that the enzyme belongs to the glycoside hydrolase family 45, subfamily 2 (B. Henrissat, Centre de Recherches sur les Macromolecules Végétales, CNRS, Joseph Fourier Université, Grenoble, France, personal communication). [source] Quantification of irreversible benzene sorption in sandy materialsHYDROLOGICAL PROCESSES, Issue 17 2004Dong-Ju Kim Abstract Based on a previous study of the irreversible sorption of benzene in sandy aquifer materials, we further investigated a method to quantify an irreversible sorption coefficient of aqueous benzene. Assuming that the rate of irreversible loss from the solution to the sorption sites followed first-order kinetics, the irreversible sorption coefficient was derived from a kinetic batch sorption test conducted for an appropriate soil-to-solution ratio to reflect the flow conditions imposed on a column test. Simulation results revealed that the irreversible sorption coefficient estimated from the kinetic batch test provided a good agreement with the measured data obtained from the column test, indicating that the method proposed in this study can be used to quantify the irreversible sorption coefficient. Copyright © 2004 John Wiley & Sons, Ltd. [source] An Internalist View on the Value of Life and Some Tricky Cases Relevant to itJOURNAL OF APPLIED PHILOSOPHY, Issue 1 2001Theo van Willigenburg If we understand death as the irreversible loss of the good of life, we can give meaning to the idea that for suffering patients in the end stage of their illness, life may become an evil and death no longer a threat. Life may lose its good already in the living person. But what does the good of life consist in, then? I defend an internalist view according to which the goodness of life is intrinsically related to the attitudes, concerns, interests and experiences of the person who is leading the life. This results in the contention that the core of what we understand as the value of a person's life is to be identified with what makes life go well for the person living the particular life. This internalist view does not presuppose (or imply) hedonism or mentalism, nor does it pose an experience requirement. Something may be good for you, because it is valuable as seen from your authentic viewpoint, even if you do not actually experience this goodness, or think otherwise because you are mistaken about your own well-being. To test this position, and the authenticity-requirement it includes, I discuss three cases of patients who are persistent in denying that in their life any value is left and who contend that death is no worse than further living. Internalism acknowledges that in the life of these patients there may be 'functionings' and 'beings' that are worthwhile, where the test of value is at least partially independent of subjective assessment. Still, internalism claims that something truly valuable can only contribute to the good of one's life of it has positive meaning as seen from the attitudinal viewpoint that identifies oneself. [source] Defining the transcriptome of accelerated and replicatively senescent keratinocytes reveals links to differentiation, interferon signaling, and Notch related pathways,JOURNAL OF CELLULAR BIOCHEMISTRY, Issue 2 2006Ranjan J. Perera Abstract Epidermal keratinocytes (KCs) undergo highly orchestrated morphological and molecular changes during transition from proliferative compartment into growth arrested early and late differentiation layers, prior to dying in outermost cornified layers of normal skin. Creation of stratum corneum is vital to barrier function protecting against infection. Transcriptional events in KCs regulating complex processes of differentiation and host defense required to maintain constant epidermal thickness and resistance to infection in either young or aged skin are largely unknown. Furthermore, as terminal differentiation is characterized by irreversible loss of replicative potential culminating in dead layers at the skin surface, this process may be viewed as a form of senescence. However, a complete transcriptional profile of senescent (SN) human KCs has not been previously defined to permit delineation of molecular boundaries involving differentiation and senescence. To fill this void, we utilized global transcriptional analysis of KCs maintained in vitro as either cultures of proliferating (PR) cells, early and late confluent (LC) (accelerated senescence) cultures, or KCs undergoing replicative senescence. Global gene expression profiling revealed early confluent (EC) KCs were somewhat similar to PR KCs, while prominent differences were evident when compared to LC KCs; which were also distinct from replicatively SN KCs. While confluent KCs have in common several genes regulating differentiation with replicatively SN KCs, the latter cells expressed elevated levels of genes involved in interferon signaling and inflammatory pathways. These results provide new insights into cell autonomous transcriptional-based programs operative within KCs contributing to replicative senescence, with partial sharing of genes involved in differentiation. In addition, regulation of KC senescence may involve participation of interferon signaling pathways derived from the important role of KCs in protecting skin from infection. Integrating all of the transcriptional data revealed a key role for Notch receptor mediated signaling in the confluency induced differentiation phenotype using this model system. J. Cell. Biochem. 98: 394,408, 2006. © 2006 Wiley-Liss, Inc. [source] Oral administration of a tri-therapy for central pattern generator activation in paraplegic mice: Proof-of-concept of efficacyBIOTECHNOLOGY JOURNAL, Issue 4 2010Pierre A. Guertin Dr. Abstract Spinal cord injury (SCI) is a neurological condition, for which no cure exists, typically leading to an immediate and irreversible loss of sensory and voluntary motor functions accompanied by significant health problems. We conducted proof-of-concept experiments aimed at assessing efficacy upon oral administration of a novel combination therapy for central pattern generator (CPG) activation and corresponding locomotor movement generation in completely paraplegic animals. Co-administration orally (by gavage) of buspirone, levodopa and carbidopa was found to dose-dependently induce episodes of steady weight-bearing stepping in low-thoracic (Th9/10) spinal cord-transected (Tx) mice (with no other form of assistance or training). Robust hindlimb stepping with weight-bearing capabilities was induced with the tri-therapy but not with clinically relevant doses of these compounds administered separately. These results provide evidence suggesting that this drug combination may be ideally suited to constitute a first-in-class therapy (CPG activator) for locomotor activity induction in chronic SCI individuals, given that efficacy was shown using commercially available brain-permeable small molecules, already known as safe for the treatment of various neurological indications. [source] Optimization of a finned heat sink array based on thermoeconomic analysisINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2007S. Z. Shuja Abstract The design and specification of heat sinks for electronic systems is not easily accomplished through the use of standard thermal design and analysis tools since geometric and boundary conditions are not typically known in advance. A second-law based thermoeconomic optimization procedure is presented for a finned heat sink array. This involves including costs associated with material, and irreversible losses due to heat transfer and pressure drop. The influence of important physical, geometrical and unit cost parameters on the overall finned array are optimized for some typical operating conditions that are representative of electronic cooling applications. The optimized cost results are presented in terms of ReD, ReL, ,P / ,H, and q for a finned system in a graphical form. In addition the methodology of obtaining optimum parameters for a finned heat sink system which will result in minimum operating cost is demonstrated. Copyright © 2006 John Wiley & Sons, Ltd. [source] Securing water for people, crops, and ecosystems: New mindset and new prioritiesNATURAL RESOURCES FORUM, Issue 2 2003Sandra L Postel A fundamentally new approach to water and human development will be needed during this new century if we are to secure sufficient freshwater to meet the needs of some 9 billion people while at the same time protecting the critical ecosystem services upon which the human economy depends. Signs of unsustainable water use , including falling water tables, shrinking lakes, and the drying up of rivers and streams , are widespread and spreading. In many regions, greater modification and appropriation of freshwater systems for human purposes will yield greater costs than benefits and create the risk of irreversible losses of species and ecosystem services. A new mindset is needed to guide water use and management in this new century, one that views the human water economy as a subset of nature's water economy. Living within nature's limits will require that societies satisfy the basic needs of people and ecosystems before non-essential water demands are met. It will require on the order of a doubling of water productivity. And it will require stronger institutions to encourage equitable sharing of water to alleviate tensions within and between countries. [source] | ||||||||||||||||