Characteristic Kinetic Properties Research Articles

Selective Discrimination of VOCs Applying Gas Sensing Kinetic Analysis over a Metal Oxide-Based Chemiresistive Gas Sensor

Semiconducting metal oxide-based gas sensors have inadequate selectivity as they are responsive toward a variety of gases. Here, we report the implementation of gas sensing kinetic analysis of the sensor to identify the tested volatile organic compounds (VOCs) (2-propanol, formaldehyde, methanol, and toluene) precisely. A single chemiresistive sensor was employed having tin oxide-based hollow spheres as the sensing material, which were obtained by chemical synthesis. The gas sensing measurements were conducted in a dynamic manner where the sensor displayed excellent response with high sensitivity. Eley-Rideal model was adopted to obtain the kinetic properties of the gas sensing phenomenon through theoretical fitting of response transient curves and their corresponding kinetic parameters. The calculated characteristic kinetic properties were further examined to discriminate among different VOCs. The approach of using gas sensing kinetic analysis for multiple gas discrimination is an attractive solution to mitigate the problem of cross-sensitivity for resistive gas sensors.

모델 상수관망에 형성된 초기 생물막에서 분리한 종속영양세균의 생장 동역학 및 염소 내성

The present work quantified the growth of young biofilm in a model distribution system that was fed with chlorinated drinking water at a hydraulic retention time of 2 h. Bacterial biofilms grew on the surface of polyvinyl chloride (PVC) slides at a specific growth rate of 0.14 ± 0.09 day –1 for total bacteria and 0.16 ± 0.08 day –1 for heterotrophic bacteria, reaching 3.1 × 10⁴ cells/㎠ and 6.6 × 10³ CFU/㎠ after 10 days, respectively. The specific growth rates of biofilm-forming bacteria were found to be much higher than those of bulk-phase bacteria, suggesting that biofilm bacteria account for a major part of the bacterial production in this model system. Biofilm isolates exhibited characteristic kinetic properties, as determined by μ max and K S values using the Monod model, in a defined growth medium containing various amounts of acetate. The lowest μ max value was observed in bacterial species belonging to the genus Methylobacterium, and their slow growth seemed to confer high resistance to chlorine treatment (0.5 mg/L for 10 min). K S values (inversely related to substrate affinity) of Sphingomonas were two orders of magnitude lower for acetate carbon than those of other isolates. The Sphingomonas isolates may have obligate-oligotrophic characteristics, since the lower K S values allow them to thrive under nutrient-deficient conditions. These results provide a better understanding and control of multi-species bacterial biofilms that develop within days in a drinking water distribution system.

Study on Suitability of KOD DNA Polymerase for Enzymatic Production of Artificial Nucleic Acids Using Base/Sugar Modified Nucleoside Triphosphates

Recently, KOD and its related DNA polymerases have been used for preparing various modified nucleic acids, including not only base-modified nucleic acids, but also sugar-modified ones, such as bridged/locked nucleic acid (BNA/LNA) which would be promising candidates for nucleic acid drugs. However, thus far, reasons for the effectiveness of KOD DNA polymerase for such purposes have not been clearly elucidated. Therefore, using mutated KOD DNA polymerases, we studied here their catalytic properties upon enzymatic incorporation of nucleotide analogues with base/sugar modifications. Experimental data indicate that their characteristic kinetic properties enabled incorporation of various modified nucleotides. Among those KOD mutants, one achieved efficient successive incorporation of bridged nucleotides with a 2′-ONHCH2CH2-4′ linkage. In this study, the characteristic kinetic properties of KOD DNA polymerase for modified nucleoside triphosphates were shown, and the effectiveness of genetic engineering in improvement of the enzyme for modified nucleotide polymerization has been demonstrated.

Motile microtubule crosslinkers require distinct dynamic properties for correct functioning during spindle organization inXenopusegg extract

The organization of the microtubule cytoskeleton depends crucially on crosslinking motors that arrange microtubules in space. Kinesin-5 is such an essential motile crosslinker. It is unknown whether its organizing capacity during bipolar spindle formation depends on its characteristic kinetic properties, or whether simply crosslinking combined with any plus-end-directed motility is sufficient for its function in a physiological context. To address this question, we replaced the motor domain of Xenopus Kinesin-5 by motor domains of kinesins belonging to other kinesin subfamilies, without changing the overall architecture of the molecule. This generated novel microtubule crosslinkers with altered kinetic properties. The chimeric crosslinkers mislocalized in spindles and consequently caused spindle collapse into tightly bundled microtubule arrays. This demonstrates that plus-end directionality and microtubule crosslinking are not the only characteristics required for proper functioning of Kinesin-5 during spindle assembly in Xenopus egg extract. Instead, its motor domain properties appear to be fine-tuned for the specific function of this kinesin.

Functional properties of skinned rabbit skeletal and cardiac muscle preparations containing alpha-cardiac myosin heavy chain.

Contractile properties of skinned muscle fibres from the masseter muscle and strips of heart atrium muscle from rabbits, both containing the alpha-cardiac myosin heavy chain isoform (alpha-cardiac MHC), were investigated and compared with those of other skeletal muscle fibre types. The stretch-induced delayed force increase (stretch activation) was investigated on maximally Ca(2+)-activated skinned preparations as an index of the kinetic properties of the myosin heads of various MHC isoforms. Skeletal muscle fibres containing exclusively alpha-cardiac MHC (type alpha) and muscle strips of heart atrium showed specific kinetics of stretch activation intermediate between those of types IIA and I fibres. In agreement with available data the unloaded shortening velocity V(u) of type alpha fibres was also intermediate between that of types IIA and I fibres. Compared with skeletal muscle type alpha fibres, muscle strips of heart atrium exhibited significantly (P<0.001) faster kinetics of both stretch activation and V(u). We conclude that type alpha fibres have characteristic kinetic properties that fill the gap between the fast type II and the slow type I fibres, and the following order of velocity can be established: IIB>IID(X)>IIA>alpha>I.

On the structural and functional modularity of glycinamide ribonucleotide formyltransferases.

Glycinamide ribonucleotide formyltransferases (GARTs) are part of the de novo purine biosynthetic pathway, catalyzing the direct transfer of a formyl group from the tetrahydrofolate cofactor to the glycinamide ribonucleotide substrate. Despite the low amino acid-sequence identity between the GARTs from Escherichia coli and human, their tertiary structures are superimposable. As part of our functional studies of these enzymes, we have investigated the interchangeability of individual protein fragments or modules between the two enzymes and the functional properties of the resulting hybrids. The modular nature of GART facilitated the creation of combinatorial libraries of chimeras between the Escherichia coli and human enzymes, which were functionally selected through complementation of an auxotrophic Escherichia coli strain. From a pool of several dozen sequence distinct hybrids, six in vivo-functional fusion genes were selected, overexpressed, and purified to homogeneity. The kinetic analysis of these constructs and the comparison of their k(cat) and K(M) values to the parental enzymes suggest that the characteristic kinetic properties from the two parents are "modular encoded" and can be exchanged by domain swapping. The chimeras in general, however, are subject to temperature instability and misfolding; thus, they serve primarily as useful candidates for further rounds of optimization.

Metabolic regulation of glucose transport.

Facilitated transport of glucose across plasma membranes, a passive Na+-independent process present in all mammalian cells, is mediated by a family of homologous glycoprotein molecules that exhibit characteristic kinetic properties and are expressed in a tissue-specific manner. Because glucose is a universal energy-producing substrate, the regulation of its transport into cells is of fundamental importance in cellular homeostasis. This review is primarily focused on regulatory pathways that modulate the rate of glucose transport in response to alterations in cellular metabolism, with specific reference to conditions associated with increased demand for glucose utilization. Mechanisms mediating the regulation of glucose transport in response to a variety of other stimuli are also briefly considered.

Regulation of electron transfer by the quinone pool.

Strong evidence for a random collisional mechanism for ubiquinone-mediated electron transfer is provided by the characteristic kinetic properties of respiratory chains originally explored by Kröger, A., and Klingenberg, M. (1973), Eur. J. Biochem. 34, 313-323. A kinetic model which leads to this so-called "simple Q-pool behavior" has been described and we use this in reviewing evidence that electron transfer is diffusion-controlled as well as diffusion-coupled. We also consider mechanisms by which the kinetics of electron transfer might deviate from simple Q-pool behavior and how these might be implicated in the regulation of electron transport.

Modification of Yeast Fructose-1,6-Bisphosphatase

Phosphorylation of purified FBPase a can be demonstrated in vitro by incubation with purified cyclic AMP-dependent protein kinase from yeast in the presence of ATP, Mg2+, and cyclic AMP. The final loss of catalytic activity is about 60%, a value very similar to that found in intact cells 1–3 minutes after addition of glucose to starved yeast. The in vitro phosphorylated enzyme shows characteristic kinetic properties similar to the enzyme assayed in a crude extract from glucose-treated yeast and to FBPase-P b purified from such an extract. Incubation of FBPase a with a lysate from yeast vacuoles, containing the bulk of the proteolytic activity of yeast, shows inactivation kinetics similar to those observed after incubation of purified FBPase a with cyclic AMP-dependent protein kinase. Chymostatin and the endogenous proteinase inhibitor IB from yeast, both known as specific inhibitors of proteinase B, completely prevent the limited proteolysis of FBPase a by the vacuole lysate. Chymostatin and the endogenous proteinase inhibitor IB from yeast, both known as specific inhibitors of proteinase B, completely prevent the limited proteolysis of FBPase a by the vacuole lysate. Studies in the laboratory of Earl Stadtman have pointed to a possible biological significance of oxidative inactivation of glutamine synthetase from Escherichia coli by mixed function oxidation reactions. Interestingly, oxidative modification of one histidine residue per subunit of glutamine synthetase parallels the loss of its activity.