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Interconversion Process (interconversion + process)
Selected AbstractsFunctional transitions of F0F1 -ATPase mediated by the inhibitory peptide IF1 in yeast coupled submitochondrial particlesFEBS JOURNAL, Issue 10 2004Mikhail Galkin The mechanism of inhibition of yeast F0F1 -ATPase by its naturally occurring protein inhibitor (IF1) was investigated in submitochondrial particles by studying the IF1-mediated ATPase inhibition in the presence and absence of a protonmotive force. In the presence of protonmotive force, IF1 added during net NTP hydrolysis almost completely inhibited NTPase activity. At moderate IF1 concentration, subsequent uncoupler addition unexpectedly caused a burst of NTP hydrolysis. We propose that the protonmotive force induces the conversion of IF1-inhibited F0F1 -ATPase into a new form having a lower affinity for IF1. This form remains inactive for ATP hydrolysis after IF1 release. Uncoupling simultaneously releases ATP hydrolysis and converts the latent form of IF1-free F0F1 -ATPase back to the active form. The relationship between the different steps of the catalytic cycle, the mechanism of inhibition by IF1 and the interconversion process is discussed. [source] Side chain contributions to the interconversion of the topological isomers of guanylin-like peptidesJOURNAL OF PEPTIDE SCIENCE, Issue 6 2005Dr Axel Schulz Abstract The peptide hormones guanylin and uroguanylin are ligands of the intestinal guanylyl cyclase-C (GC-C) that is involved in the regulation of epithelial water and electrolyte transport. The small peptides contain 15 and 16 amino acids, respectively, and two disulfide bonds with a 1,3/2,4 connectivity. This structural feature causes the unique existence of two topological isoforms for each peptide in an approximate 3:2 ratio, with only one of the isoforms exhibiting GC-C-activating potential. The two uroguanylin isomers can be separated by HPLC and are of sufficient stability to be studied separately at ambient temperatures while the two guanylin isomers are rapidly interconverting even at low temperatures. Both isomers show clearly distinguishable 1H chemical shifts. To investigate the influence of certain amino acid side chains on this isomerism and interconversion kinetics, derivatives of guanylin and uroguanylin (L -alanine scan and chimeric peptides) were designed and synthesized by Fmoc solid-phase chemistry and compared by HPLC and 2D 1H NMR spectroscopy. Amino acid residues with the most significant effects on the interconversion kinetics were predominantly identified in the COOH-terminal part of both peptides, whereas amino acids in the central part of the peptides only moderately affected the interconversion. Thus, the conformational conversion among the isomers of both peptides is under the control of a COOH-terminal sterical hindrance, providing a detailed model for this dynamic isomerism. Our results demonstrate that kinetic control of the interconversion process can be achieved by the introduction of side chains with a defined sterical profile at suitable sequence positions. This is of potential impact for the future development of GC-C peptide agonists and antagonists. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source] The stereodynamics of 1,2-dipropyldiaziridinesCHIRALITY, Issue 2 2010Oliver Trapp Abstract N-alkylated trans -diaziridines are an intriguing class of compounds with two stereogenic nitrogen atoms which easily interconvert. In the course of our investigations of the nature of the interconversion process via nitrogen inversion or electrocyclic ring opening ring closure, we synthesized and characterized the three constitutionally isomeric diaziridines 1,2-di- n -propyldiaziridine 1, 1-isopropyl-2- n -propyldiaziridine 2, and 1,2-diisopropyldiaziridine 3 to study the influence of the substituents on the interconversion barriers. Enantiomer separation was achieved by enantioselective gas chromatography on the chiral stationary phase Chirasil-,-Dex with high separation factors , (1-isopropyl-2- n -propyldiaziridine: 1.18; 1, 2-diisopropyldiaziridine: 1.24; 100°C 50 kPa He) for the isopropyl substituted diaziridines. These compounds showed pronounced plateau formation between 100 and 150°C, and peak coalescence at elevated temperatures. The enantiomerization barriers ,G, and activation parameters ,H, and ,S, were determined by enantioselective dynamic gas chromatography (DGC) and direct evaluation of the elution profiles using the unified equation implemented in the software DCXplorer. Interestingly, 1-isopropyl-2- n -propyldiaziridine and 1,2-diisopropyldiaziridine exhibit similar high interconversion barriers ,G, (100°C) of 128.3 ± 0.4 kJ mol,1 and 129.8 ± 0.4 kJ mol,1, respectively, which indicates that two sterically demanding substituents do not substantially increase the barrier as expected for a distinct nitrogen inversion process. Chirality, 2010. © 2009 Wiley-Liss, Inc. [source] Protein expression changes induced in murine peritoneal macrophages by Group B StreptococcusPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 11 2010Federica Susta Abstract Protein expression changes induced in thioglycolate-elicited peritoneal murine macrophages (M,) by infection with type III Group B Streptococcus (GBS) are described. Proteins from control M, and M, incubated 2,h with live or heat-inactivated GBS were separated by 2-DE. Proteins whose expression was significantly different in infected M,, as compared with control cells, were identified by MS/MS analysis. Changes in the expression level of proteins involved in both positive and negative modulation of phagocytic functions, stress response and cell death were induced in M, by GBS infection. In particular, expression of enzymes playing a key role in production of reactive oxygen species was lowered in GBS-infected M,. Significant alterations in the expression of some metabolic enzymes were also observed, most of the glycolytic and of the pentose-cycle enzymes being down-regulated in M, infected with live GBS. Finally, evidence was obtained that GBS infection affects the expression of enzymes or enzyme subunits involved in ATP synthesis and in adenine nucleotides interconversion processes. [source] Metallocyclo- and Polyphosphazenes Containing Gold or Silver: Thermolytic Transformation into Nanostructured MaterialsCHEMISTRY - A EUROPEAN JOURNAL, Issue 48 2009Josefina Jiménez Dr. Abstract A cyclotriphosphazene bearing two 4-oxypyridine groups on the same phosphorus atom, gem -[N3P3(O2C12H8)2(OC5H4N-4)2] (I), and its analogous polymer [{NP(O2C12H8)}0.7{NP(OC5H4N-4)2}0.3]n (II), have been used to prepare gold or silver, cyclic and polymeric, metallophosphazenes. The following complexes, gem -[N3P3(O2C12H8)2(OC5H4N-4{ML})2] (ML=Au(C6F5) (1) or Au(C6F5)3 (2)), [N3P3(O2C12H8)2(OC5H4N-4{AuPPh3})2][NO3]2 (3), and [N3P3(O2C12H8)2(OC5H4N-4{AgPPh2R})2][SO3CF3]2 (R=Ph (4) or Me (5)) have been obtained. Complexes 1 and 4 are excellent models for the preparation of the analogous polymers [{NP(O2C12H8)}0.7{NP(OC5H4N-4{ML})2}0.3]n (ML=Au(C6F5) (P1), Ag(OSO2CF3)PPh3 (P2)). All complexes have been characterized by elemental analysis, various spectroscopic methods, and mass spectrometry. The polymers were further investigated by thermochemical methods (thermogravimetric analysis) and differential scanning calorimetry. For compounds 1,5 and for the starting phosphazene I, a mixture of different stereoisomers may be expected. The stereochemistry in solution has been studied by variable-temperature NMR spectroscopy studies, which provided evidence for interconversion processes that involve changes in the chirality of a 2,2,-dioxybiphenyl group. A single-crystal X-ray analysis of the gold complex 2 confirmed not only the proposed structure, but also S,S and R,R configurations at the two biphenoxy-substituted phosphorus centers, in contrast to those observed for the precursor I. Pyrolysis of these new metallophosphazenes was also studied. Notably, pyrolysis of the gold derivatives gave macroporous metallic gold sponges without the requirement of either an external reducing agent or a porous support. These materials were all characterized by XRD, TEM, SEM, and energy-dispersive X-ray spectroscopy. En este trabajo se ha usado el ciclotrifosfazeno que tiene dos grupos 4-oxipiridina en el mismo átomo de fósforo, gem -[N3P3(O2C12H8)2(OC5H4N-4)2] (I), y su polímero análogo, [{NP(O2C12H8)}0.7{NP(OC5H4N-4)2}0.3]n(II), para preparar nuevos compuestos de oro o plata, cíclicos o polímeros. Se han obtenido los siguientes complejos, gem -[N3P3(O2C12H8)2(OC5H4N-4{ML})2] [ML=Au(C6F5) (1), Au(C6F5)3 (2)], [N3P3(O2C12H8)2(OC5H4N-4{AuPPh3})2][NO3]2 (3) and [N3P3(O2C12H8)2(OC5H4N-4{AgPPh2R})2][SO3CF3]2 [R=Ph (4) or Me (5)], que a su vez han resultado ser excelentes modelos para preparar los polímeros análogos de oro o plata, [{NP(O2C12H8)}0.7{NP(OC5H4N-4{ML})2}0.3]n[ML=Au(C6F5)(P1), Ag(OSO2CF3)PPh3 (P2)]. Todos los complejos, cíclicos o polímeros, se han caracterizado por análisis elemental, por métodos espectroscópicos y por espectrometría de masas. Los polímeros, además, se han caracterizado por métodos termoquímicos (TGA y DSC). Para 1,5 y para el fosfazeno de partida (I) puede esperarse una mezcla de varios estereoisómeros. Se ha estudiado su estereoquímica en disolución por RMN a temperatura variable, lo que ha indicado la presencia de un proceso de interconversión que implica cambios de quiralidad del grupo 2,2,-dioxibifenilo. La resolución de la estructura cristalina del complejo 2, por difracción de Rayos X, no sólo ha confirmado la estructura propuesta sino que, además, indica una configuración (S,S)- y (R,R)- , a diferencia de lo observado para el precursor I. Se ha estudiado también la pirólisis de estos nuevos metalofosfazenos. Cabe destacar que la pirólisis de los derivados de oro, trímero (1) y polímero (P1), dio esponjas macroporosas de oro metálico sin utilizar un agente reductor externo ni un soporte poroso. Todos estos materiales se han caracterizado por XRD, TEM, SEM y EDAX. [source] | ||||||||||