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81.
Polyoxometalates (POMs)containingKegginmoi etieshavebeenreceivingextensiveattentioninrecentyearsowingtotheirgreatfundamentalandpracticalinter est .1Especiallytheunusualelectronicproperty (highnegativecharges) ,oneofthemostimportantpropertiesofPOMs ,haspoten… 相似文献
82.
The time-resolved tryptophyl fluorescence of alpha-chymotrypsin A and alpha-chymotrypsin in the crystalline state and in buffer solution at room temperature was analyzed globally. Triple-exponential decay functions are necessary to adequately describe the tryptophyl fluorescence decay surfaces of the protein powders as a function of hydration and in solution. The fluorescence lifetimes of alpha-chymotrypsinogen A (tau 1 = 0.32, tau 2 = 1.30 ns, tau 3 = 3.98 ns) and alpha-chymotrypsin(tau 1 = 0.66 n s, tau 2 = 2.26 ns, tau 3 = 5.40 ns) are constant over the entire hydration range. The spectral positions of the decay-associated spectra of the hydrated powders do not shift as a function of hydration. This indicates that the structures of the zymogen and the active enzyme are unaffected by hydration. The lifetimes of alpha-chymotrypsinogen A in phosphate buffer pH 7.4 are tau 1 = 0.37 ns, tau 2 = 1.17 ns and tau 3 = 3.44 ns while the respective values of alpha-chymotrypsin are tau 1 = 0.47 ns, tau 2 = 1.40 and tau 1 = 3.89 ns. 相似文献
83.
Lee HY Chung HS Hang C Khosla C Walsh CT Kahne D Walker S 《Journal of the American Chemical Society》2004,126(32):9924-9925
EryCIII converts alpha-mycarosyl erythronolide B into erythromycin D using TDP-d-desosamine as the glycosyl donor. We report the heterologous expression, purification, in vitro reconstitution, and preliminary characterization of EryCIII. Coexpression of EryCIII with the GroEL/ES chaperone complex was found to enhance greatly the expression of soluble EryCIII protein. The enzyme was found to be highly active with a kcat greater than 100 min-1. EryCIII was quite selective for the natural nucleotide sugar donor and macrolide acceptor substrates, unlike several other antibiotic glycosyl transferases with broad specificity such as desVII, oleG2, and UrdGT2. Within detectable limits, neither 6-deoxyerythronolide B nor 10-deoxymethynolide were found to be glycosylated by EryCIII. Furthermore, TDP-d-mycaminose, which only differs from TDP-d-desosamine at the C4 position, could not be transferred to alphaMEB. These studies lay the groundwork for detailed structural and mechanistic analysis of an important member of the desosaminyl transferase family of enzymes. 相似文献
84.
Youngseon Park Dr. Atsushi Taguchi Dr. Vadim Baidin Prof. Daniel Kahne Prof. Suzanne Walker 《Angewandte Chemie (International ed. in English)》2023,62(25):e202301522
The peptidoglycan cell wall is essential for bacterial survival. To form the cell wall, peptidoglycan glycosyltransferases (PGTs) polymerize Lipid II to make glycan strands and then those strands are crosslinked by transpeptidases (TPs). Recently, the SEDS (for shape, elongation, division, and sporulation) proteins were identified as a new class of PGTs. The SEDS protein FtsW, which produces septal peptidoglycan during cell division, is an attractive target for novel antibiotics because it is essential in virtually all bacteria. Here, we developed a time-resolved Förster resonance energy transfer (TR-FRET) assay to monitor PGT activity and screened a Staphylococcus aureus lethal compound library for FtsW inhibitors. We identified a compound that inhibits S. aureus FtsW in vitro. Using a non-polymerizable Lipid II derivative, we showed that this compound competes with Lipid II for binding to FtsW. The assays described here will be useful for discovering and characterizing other PGT inhibitors. 相似文献
85.
Hu Y Al-Mestarihi A Grimes CL Kahne D Bachmann BO 《Journal of the American Chemical Society》2008,130(47):15756-15757
Herein we describe the cloning, functional expression and initial characterization of ORF36 from Micromonospora carbonacae var. africana and rubN8 from Streptomyces achromogenes var. rubradiris. The purified enzymes play the same role, the double-oxidation of TDP-evernosamine to TDP-evernitrosose in the everninomycin and rubradirin pathways, respectively. 相似文献
86.
JUAN E. PERALTA VERÓNICA BARONE MARTÍN C. RUIZ DE AZÚA RUBÉN H. CONTRERAS 《Molecular physics》2013,111(8):655-661
In this work an implementation of the FPT-DFT approach for calculating the spin-dipolar contribution to NMR spin-spin coupling constants is presented. This method was tested in a set of small molecules, giving results in excellent agreement when comparing them with values taken from the literature, which were obtained with state-of-the-art calculations. To obtain an insight into the relative importance of the spin-dipolar contribution in unsaturated compounds, calculations of J(F,C), J(F,F) and J(F,H) couplings in 1,2-, 1,3-, and 1,4-difluorobenzenes were performed. An important spin-dipolar contribution to 3 J(F, F) and 5 J(F,F) was found, suggesting that this term might be important in some cases. When performing DFT calculations the non-singlet instabilities usually found in unsaturated compounds are overcome. 相似文献
87.
Better substrates for bacterial transglycosylases. 总被引:2,自引:0,他引:2
88.
EDUARDO DE RAFAEL 《Pramana》2012,78(6):927-946
In the large-N c limit of QCD, two-point functions of local operators become harmonic sums. I review some properties which follow from this fact and which are relevant for phenomenological applications. This has led us to consider a class of analytic number theory functions as toy models of large-N c QCD which also is discussed. 相似文献
89.
The most potent inhibitor of the p53-MDM2 interaction reported to date is an 8-mer p53 peptide analogue (Novartis peptide), which contains 6-chlorotryptophane (Cl-Trp) and phosphonomethylphenylalanine (Pmp) as key residues for the enhanced activity. We report here a crystal structure of the co-complex between MDM2 and the Novartis peptide solved at 1.8 A resolution. The structural basis for the role of the two aromatic residues are delineated by comparing the present structure with crystal structures of the MDM2 co-complex bound to other inhibitors including the wt-p53 peptide itself. 相似文献
90.
Deon DE Wet‐Roos Aletta DU Toit Dawie J. Joubert 《Journal of polymer science. Part A, Polymer chemistry》2006,44(23):6847-6856
Homogeneous tandem catalysis of the bis(diphenylphoshino)amine‐chromium oligomerization catalyst with the metallocenes Ph2C(Cp)(9‐Flu)ZrCl2 and rac‐EtIn2ZrCl2, is discussed. GC, CRYSTAF, and 13C NMR analysis of the products obtained from reactions at constant temperatures show that during tandem catalysis, α‐olefins, mainly 1‐hexene and 1‐octene, are produced from ethylene by the oligomerization catalyst and subsequently built into the polyethylene chain. At 40 °C the Cr/PNP catalyst acts as a tetramerization catalyst while the polymerization catalyst activity is low. Copolymerization of ethylene and the in situ produced α‐olefins have also been carried out by increasing the temperature from 40 °C, where primarily oligomerization takes place, to above 100 °C, where polymerization becomes dominant. The melting temperature of the polymer is dependent on the catalyst and cocatalyst ratios as well as on the temperature gradient followed during the reaction, while the presence of the oligomerization catalyst reduces the activity of the polymerization catalyst. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6847–6856, 2006 相似文献