172,260 research outputs found
Proteins from the prokaryotic nucleoid: 1H NMR study of the quaternary structure of Escherichia coli DNA binding protein NS (HU)
No full textThe quaternary interactions of Escherichia coli DNA binding proteins NS1, NS2, and NS (NS1 + NS2) have been studied by 1H NMR spectroscopy at 400 MHz following the reversible spectral changes produced by temperature increases on the resonances (Phe ring and His C-2 protons) whose spectral characteristics reflect the formation and dissociation of either homologous or heterologous interactions. These changes include (a) a progressive intensity decrease of the Phe resonances shifted to high field by stacking interactions, (b) a progressive intensity increase of the resonances due to freely rotating Phe, and (c) splitting of the His C-2 proton resonance. The association constants and thermodynamic parameters for the homologous and heterologous interactions were calculated from the molar fractions of the relevant molecular species by assuming that the above effects are due to the existence of simple association equilibria. It was found that two (out of three) phenylalanine residues of each polypeptide chain are involved in quaternary interactions. Quantitative data concerning the internal mobility and mutual orientations in aggregates of these Phe rings were also obtained. From the calculated association constants, from comparison of these data with recent protein-protein cross-linking results [Losso, M. A., Pawlik, R. T., Canonaco, M. A., & Gualerzi, C. O. (1986) Eur. J. Biochem. 155, 27-32], and from other considerations, we suggest that even though stacking of the Phe rings occurs at the interface between monomers, the temperature-dependent alteration of the Phe spectrum monitors shifts of the dimer in equilibrium tetramer equilibrium whereas the splitting of the His C-2 proton resonance most likely monitors the equilibrium between tetramers and larger aggregates
The interaction between initiation factor 3 and 30 S ribosomal subunits studied by high-resolution 1H NMR spectroscopy
No full textThe interaction between Escherichia coli translational initiation factor 3 (IF-3) (Mr = 20668) and 30 S ribosomal subunits or fragmented 16 S rRNA was followed by 1H NMR spectroscopy. Upon addition of increasing yet largely substoichiometric amounts of deuterated 30 S ribosomal subunits, selective line broadenings and some chemical shift changes were observed. These effects can be fully reversed by increasing the temperature and/or the ionic strength. The selective line broadenings, which are explained by a medium-fast to fast exchange dynamics between free and bound IF-3 with loss of internal mobility of the protons, shed light on the amino acid residues of IF-3 involved in or affected by the binding to the 30 S subunits. Some effects (i.e. implication of 1 tyrosine, 1 phenylalanine, and some arginine and lysine residues) are seen with both 30 S subunits and rRNA while others (i.e. implication of a second tyrosine or phenylalanine residue of a group of hydrophobic residues and, possibly, of the single histidine residue), seen only or preferentially with 30 S subunits, may reflect additional interactions exclusively occurring at the ribosomal level
Unconventional pairing in fullerides by nonadiabatic channels
No full textIn C-60 compounds the frequencies of the phonon involved in the superconductive processes (intra-molecular modes with omega(ph) up to 2300 K) are comparable with the typical electronic scale (E-F = 2900 K) and thus the two dynamics cannot be treated separately (breakdown of the adiabatic hypothesis). This implies a generalization of the standard theory to include nonadiabatic effects. The strong electronic correlation in the fullerenes causes the contribution of the nonadiabatic processes to be positive with consequent increase of the effective electron-phonon (el-ph) pairing;, and of T-c. We show that the inclusion of nonadiabatic terms in the el-ph interaction is a key element for the high values of T, in fullerenes. In particular T-c as high as 100 K are shown to be compatible with moderate values of lambda less than or similar to 1. This implies that it should be possible to increase the value of lambda, and so T-c, and still have a stable system. (C) 2004 Elsevier B.V. All rights reserved
EFEKTIFITAS PEMANFATAAN LARUTAN PACI-PACI (LEUCAS LAVANDULAEFOLIA) TERHADAP PERKEMBANGAN POPULASI PARASIT (TRICHODINA SP) PADA IKAN LELE DUMBO (CLARIAS SP)
No full textThis study aims to determine the effectiveness of the solution to the abundance paci- paci Trichodina sp that attack catfish. This research is expected to be material information in an effort to increase fish production in the African catfish hatchery operations. This study was conducted in August and September 2015 Fish Seed Center (BBI) Bontomanai Gowa in South Sulawesi, The experimental design used was completely randomized design (CRD) with 4 treatments and 3 replications ie Treatment A (1.000 ppm), treatment B (2,000 ppm), treatment C (3,000 ppm), and without giving a solution of PACI - Paci (treatment D). The results showed that soaking in the solution catfish paci paci leaf extract is effective to reduce the infestation Trichodina to 84%, and the best dose in this study with a 24-hour immersion is 3 g / l.dengan this treatment achieved a survival rate higher catfish during immersion, ie 97%
Theologia christiana dogmatico-moralis : de iure nat. et gen. & c adversus Puffend. Barbeyr. Thomas. aliosque novatores tomus sextus
No full textSign.: a-b, c, A-Z, 2A-2Z, 3APort. con grav. xilTexto a dúas co
Electron-Paramagnetic-Resonance and H-1 and C-13 NMR-study of paper
No full textHigh quality antique sheets of paper have been characterized by H-1 NMR relaxation, C-13 CP MAS spectra, and Electron Paramagnetic Resonance spectroscopy. Paper can be regarded as a bi-component material made by cellulose and water plus a small amount of organic and inorganic additives and impurities. Semi-crystalline fibrous cellulose, rich in water, is present as polymorphs I alpha and I beta. Amorphous cellulose, with a lower water content, presents a higher amount of paramagnetic impurities and is characterized by quite short H-1 spin-lattice relaxation times and by C-13 resonances with noticeable chemical shifts. ''Ad hoc'' tailored sequences are able to produce C-13 CP MAS spectra in which the amorphous content of cellulose in paper is quite well observable. The nature of water as fully bound to the cellulose lattice has also been proved. Low-temperature EPR spectra have shown the presence of measurable amounts of different inorganic paramagnetic impurities, such as Fe3+, Mn2+, Cu2+ often found in different stereochemical environments. The spectra are all, qualitatively, closely similar. However, quantitative data have shown that in paper the state of conservation does not depend on the amount of pseudo-octahedral iron, but is strongly correlated to the concentration of this metal ion in a rhombic stereochemistry and to the presence of even very small amounts of copper
Structure-function relationship in Escherichia coli initiation factors. Biochemical and biophysical characterization of the interaction between IF-2 and guanosine nucleotides
No full textEquilibrium dialysis and protection from heat inactivation and proteolysis show that initiation factor 2 (IF-2) interacts not only with GTP but also with GDP and that its conformation is changed upon binding of either nucleotide. The apparent Ka (at 25 degrees C) for the IF-2 X GDP and IF-2 X GTP complexes was 8.0 X 10(4) and 7.0 X 10(3) M(-1), respectively. The lower affinity for GTP is associated with a more negative delta S0. The interaction, monitored by 1HNMR spectroscopy, is characterized by fast exchange and results in line broadening and downfield shift of the purine C-8 and ribose C-1' protons of GTP as well as of the beta, gamma-methylene protons of (beta-gamma-methylene)guanosine 5'-triphosphate. The interaction of guanosine nucleotides with IF-2 requires an H bond donor (or acceptor) group at position C-2 of the purine and involves the beta- and/or gamma-phosphate of the nucleotide while the ribose 2'-OH group or the integrity of the furan ring are less critical. IF-2 binds to ribosomal particles with decreasing affinity: 30 S greater than 70 S greater than 50 S. GTP and GDP have no effect on the binding to 70 S. GTP stimulates the binding to the 30 S and depresses somewhat the binding to the 50 S subunits; GDP has the opposite effect. These results seem to rule out that the release of IF 2 from 70 S is due to a "GDP-conformation" of the factor incompatible with its permanence on the ribosome. The rate and the extent of 30 S initiation complex formation are approximately 2-fold higher with IF-2 X GTP than with IF-2 alone. At low concentrations of IF-2 and 30 S subunits, GDP inhibits this reaction, acting as a strong competitive inhibitor of GTP (Ki = 1.25 X 10(-5)m) and preventing IF-2 from binding to the ribosomal subunit
- …
