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  • Bradyrhizobium japonicum  (1)
  • Conformational analysis  (1)
  • Hybrid methods  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Journal of molecular modeling 6 (2000), S. 527-538 
    ISSN: 0948-5023
    Schlagwort(e): Hybrid methods ; QM/MM ; LSCF ; Zinc metalloproteases ; Thermolysin ; Peptide hydrolysis ; Enzymatic mechanism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The hydrolysis by thermolysin of a Gly-Phe-Leu peptide, considered as a model substrate of the enkephalin family, has been studied with a mixed QM/MM method with the AM1/AMBER parameterization. This study is based on the mechanism proposed by Matthews in which the Glu-143 residue plays the role of a proton shuttle in the course of the reaction. The study focused on the description of every step of the process, reaction intermediates and transition states, and on the influence, both energetical and structural, of the whole protein on these stationary points. The overall mechanism appears to be quite realistic, but the study shows that some reaction steps that were assumed to be concerted should occur in two phases. Analysis of the role of the amino-acids surrounding the active site has shown their important participation in the fluctuations of the energy. In particular, the major role of His-231 on the overall mechanism has been confirmed. This study shows that modeling reaction mechanisms for enzymes is quite feasible and opens the way for computer experiments that may be helpful in devising and interpreting detailed experimental investigations.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 1432-072X
    Schlagwort(e): Bradyrhizobium japonicum ; Nitrate ; Membrane-bound nitrate reductase ; Nitrate reductase mutants ; Microaerobiosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Native PAGE of Triton x-100-solubilized membranes from Bradyrhizobium japonicum strain PJ17 grown microaerobically (2% O2, v/v) in defined nitrate-containing medium resolved two catalytically active nitrate reductase (NR) species with apparent molecular masses of 160 kDa (NRI) and 200 kDa (NRII). NRI and NRII were also found in membranes from cells of strain PJ17 that were first grown in defined medium with glutamate and further incubated microaerobically in the presence of 5 mmol/l KNO3. However, only NRI was detected in cell membranes of strain PJ17 when nitrate was omitted from the microaerobic incubation medium. Four mutants unable to grow at low O2 tension in the presence of nitrate were isolated after transposon Tn5 mutagenesis. Membranes from mutants GRF110 and GRF116 showed mainly NRI, while the other two mutants, GRF3 and GRF4, expressed mostly NRII. These results indicate that the ability of B. japonicum PJ17 to grow under microaerobic conditions depends upon the presence of two membrane-bound NR enzymes whose synthesis seem to be independently induced by microaerobiosis (NRI) or by both microaerobiosis and nitrate (NRII).
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Journal of computer aided molecular design 7 (1993), S. 183-198 
    ISSN: 1573-4951
    Schlagwort(e): QSAR ; Conformational analysis ; Prostaglandin synthase ; Antiinflammatory ; Amfenac
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The new nonsteroidal antiinflammatory drug (NSAID) arylacetic amfenac (2-amino-3-benzoylphenylacetic acid) and 19 substituted derivatives were studied in order to correlate the biological activities with the structure-related parameters. The geometry of amfenac in neutral and anionic form was totally optimized, starting from standard geometries and crystallographic data, using semiempirical AM1 and MNDO quantum-mechanical methods. Conformational analysis shows the existence of a rigid structure for rotations of the acetic acid chain (α°) and the central carbonyl group (γ°) around the bonds with the phenylamine ring, whereas the carboxyl group (β°) and the phenyl ring of the benzoyl group (δ°) can rotate almost freely. Electrostatic potential maps were analyzed and showed that the electrostatic orientation effect seems to make an important contribution to the binding of the active compounds to prostaglandin synthase. An electrostatic orientation model of the binding site is proposed. The frontier orbital charge distribution was also described for each compound. On the other hand, steric, electronic and hydrophobic (log P) parameters were calculated and QSAR analysis showed that the most significant parameter for the antiinflammatory activity was the π-electron density of the HOMO orbital in the second aromatic ring. These results suggest a possible electronic charge transfer between the aromatic fragments and the receptor.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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