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Reversible Conversion (reversible + conversion)
Selected AbstractsMetal Coordination Mediated Reversible Conversion between Linear and Cross-Linked Supramolecular Polymers,ANGEWANDTE CHEMIE, Issue 6 2010Feng Wang Dr. Dynamisches Duo: Dynamische supramolekulare Polymere mit unterschiedlichen Topologien, z.,B. lineare und vernetzte Strukturen (siehe Schema), können reversibel ineinander umgewandelt werden. Als externe Auslöser dienen nichtkovalente Wirt-Gast- und Metall-Ligand-Erkennungsmotive. [source] Self-Assembly of a Two-Dimensional Bimetallic Coordination Framework and Dynamic Control of Reversible Conversions to Homo-Metallic Hydrogen-Bond ArraysCHEMPHYSCHEM, Issue 1 2010Ziliang Shi A novel 2D coordination bimetallic framework composed of Cu and Zn is obtained at a Au(111) surface by the supramolecular assembly of Cu and zinc-5,10,15,20-tetra(4-pyridyl)porphyrin molecules (see figure). Suppressing Cu concentration at high temperature transforms the 2D bimetallic frameworks into 2D homo-metallic hydrogen-bond arrays. Enriching the Cu concentration can reverse the structural transformation. [source] Characterization of cinnamyl alcohol dehydrogenase of Helicobacter pyloriFEBS JOURNAL, Issue 5 2005An aldehyde dismutating enzyme Cinnamyl alcohol dehydrogenases (CAD; 1.1.1.195) catalyse the reversible conversion of p -hydroxycinnamaldehydes to their corresponding alcohols, leading to the biosynthesis of lignin in plants. Outside of plants their role is less defined. The gene for cinnamyl alcohol dehydrogenase from Helicobacter pylori (HpCAD) was cloned in Escherichia coli and the recombinant enzyme characterized for substrate specificity. The enzyme is a monomer of 42.5 kDa found predominantly in the cytosol of the bacterium. It is specific for NADP(H) as cofactor and has a broad substrate specificity for alcohol and aldehyde substrates. Its substrate specificity is similar to the well-characterized plant enzymes. High substrate inhibition was observed and a mechanism of competitive inhibition proposed. The enzyme was found to be capable of catalysing the dismutation of benzaldehyde to benzyl alcohol and benzoic acid. This dismutation reaction has not been shown previously for this class of alcohol dehydrogenase and provides the bacterium with a means of reducing aldehyde concentration within the cell. [source] Nonvolatile Memory: Majority Carrier Type Conversion with Floating Gates in Carbon Nanotube Transistors (Adv. Mater.ADVANCED MATERIALS, Issue 47 200947/2009) A charge trapping layer can serve not only for designing multilevel nonvolatile memory but also for reversible type conversion from p- to n-type in carbon nanotube channels. Young Hee Lee and co-workers demonstrate on p. 4821 that reversible conversion from p- to n-type can be robustly realized in CNT field-effect transistors by changing the polarity of trapped charges. [source] Sucrose phosphorylase of the rumen bacterium Pseudobutyrivibrio ruminis strain AJOURNAL OF APPLIED MICROBIOLOGY, Issue 3 2009A. Kasperowicz Abstract Aims:, To verify the taxonomic affiliation of bacterium Butyrivibrio fibrisolvens strain A from our collection and to characterize its enzyme(s) responsible for digestion of sucrose. Methods and Results:, Comparison of the 16S rRNA gene of the bacterium with GenBank showed over 99% sequence identity to the species Pseudobutyrivibrio ruminis. Molecular filtration, native electrophoresis on polyacrylamide gel, zymography and thin layer chromatography were used to identify and characterize the relevant enzyme. An intracellular sucrose phosphorylase with an approximate molecular mass of 52 kDa exhibiting maximum activity at pH 6·0 and temperature 45°C was identified. The enzyme was of inducible character and catalysed the reversible conversion of sucrose to fructose and glucose-1-P. The reaction required inorganic phosphate. The Km for glucose-1-P formation and fructose release were 3·88 × 10,3 and 5·56 × 10,3 mol l,1 sucrose, respectively , while the Vmax of the reactions were ,0·579 and 0·9 ,mol mg protein,1 min,1. The enzyme also released free glucose from glucose phosphate. Conclusion:,Pseudobutyrivibrio ruminis strain A utilized sucrose by phosphorolytic cleavage. Significance and Impact of the Study:, Bacterium P. ruminis strain A probably participates in the transfer of energy from dietetary sucrose to the host animal. [source] Lutein epoxide cycle, light harvesting and photoprotection in species of the tropical tree genus IngaPLANT CELL & ENVIRONMENT, Issue 4 2008SHIZUE MATSUBARA ABSTRACT Dynamics and possible function of the lutein epoxide (Lx) cycle, that is, the reversible conversion of Lx to lutein (L) in the light-harvesting antennae, were investigated in leaves of tropical tree species. Photosynthetic pigments were quantified in nine Inga species and species from three other genera. In Inga, Lx levels were high in shade leaves (mostly above 20 mmol mol,1 chlorophyll) and low in sun leaves. In Virola surinamensis, both sun and shade leaves exhibited very high Lx contents (about 60 mmol mol,1 chlorophyll). In Inga marginata grown under high irradiance, Lx slowly accumulated within several days upon transfer to deep shade. When shade leaves of I. marginata were briefly exposed to the sunlight, both violaxanthin and Lx were quickly de-epoxidized. Subsequently, overnight recovery occurred only for violaxanthin, not for Lx. In such leaves, containing reduced levels of Lx and increased levels of L, chlorophyll fluorescence induction showed significantly slower reduction of the photosystem II electron acceptor, QA, and faster formation as well as a higher level of non-photochemical quenching. The results indicate that slow Lx accumulation in Inga leaves may improve light harvesting under limiting light, while quick de-epoxidation of Lx to L in response to excess light may enhance photoprotection. [source] X-ray structure and characterization of carbamate kinase from the human parasite Giardia lambliaACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 4 2010Andrey Galkin Carbamate kinase catalyzes the reversible conversion of carbamoyl phosphate and ADP to ATP and ammonium carbamate, which is hydrolyzed to ammonia and carbonate. The three-dimensional structure of carbamate kinase from the human parasite Giardia lamblia (glCK) has been determined at 3,Å resolution. The crystals belonged to the monoclinic space group P21, with unit-cell parameters a = 69.77, b = 85.41, c = 102.1,Å, , = 106.8°. The structure was refined to a final R factor of 0.227. The essentiality of glCK together with its absence in humans makes the enzyme an attractive candidate for anti- Giardia drug development. Steady-state kinetic rate constants have been determined. The kcat for ATP formation is 319 ± 9,s,1. The Km values for carbamoyl phosphate and ADP are 85 ± 6 and 70 ± 5,µM, respectively. The structure suggests that three invariant lysine residues (Lys131, Lys216 and Lys278) may be involved in the binding of substrates and phosphoryl transfer. The structure of glCK reveals that a glycerol molecule binds in the likely carbamoyl phosphate-binding site. [source] The structure of an archaeal ribose-5-phosphate isomerase from Methanocaldococcus jannaschii (MJ1603)ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 12 2009Richard W. Strange Ribose-5-phosphate isomerase is a ubiquitous intracellular enzyme of bacterial, plant and animal origin that is involved in the pentose phosphate cycle, an essential component of cellular carbohydrate metabolism. Specifically, the enzyme catalyses the reversible conversion of ribose 5-phosphate to ribulose 5-phosphate. The structure of ribose-5-phosphate isomerase from Methanocaldococcus jannaschii has been solved in space group P21 to 1.78,Å resolution using molecular replacement with one homotetramer in the asymmetric unit and refined to an R factor of 14.8%. The active site in each subunit was occupied by two molecules of propylene glycol in different orientations, one of which corresponds to the location of the phosphate moiety and the other to the location of the furanose ring of the inhibitor. [source] Structure of d -3-hydroxybutyrate dehydrogenase prepared in the presence of the substrate d -3-hydroxybutyrate and NAD+ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 4 2009Md Mominul Hoque d -3-Hydroxybutyrate dehydrogenase from Alcaligenes faecalis catalyzes the reversible conversion between d -3-hydroxybutyrate and acetoacetate. The enzyme was crystallized in the presence of the substrate d -3-hydroxybutyrate and the cofactor NAD+ at the optimum pH for the catalytic reaction. The structure, which was solved by X-ray crystallography, is isomorphous to that of the complex with the substrate analogue acetate. The product as well as the substrate molecule are accommodated well in the catalytic site. Their binding geometries suggest that the reversible reactions occur by shuttle movements of a hydrogen negative ion from the C3 atom of the substrate to the C4 atom of NAD+ and from the C4 atom of NADH to the C3 atom of the product. The reaction might be further coupled to the withdrawal of a proton from the hydroxyl group of the substrate by the ionized Tyr155 residue. These structural features strongly support the previously proposed reaction mechanism of d -3-hydroxybutyrate dehydrogenase, which was based on the acetate-bound complex structure. [source] | |||||||||||||