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941.
Xian-He Bu He LiuMiao Du Keith Man-Chung WongVivian Wing-Wah Yam 《Inorganica chimica acta》2002,333(1):32-40
The complexes of Cu(I), Cu(II), Ni(II), Zn(II) and Co(II) with a new polypyridyl ligand, 2,3-bis(2-pyridyl)-5,8-dimethoxyquinoxaline (L), have been synthesized and characterized. The crystal structures of these complexes have been elucidated by X-ray diffraction analyses and three types of coordination modes for L were found to exist in them. In the dinuclear complex [Cu(I)L(CH3CN)]2·(ClO4)2 (1), L acts as a tridentate ligand with two Cu(I) centers bridged by two L ligands to form a box-like dimeric structure, in which each Cu(I) ion is penta-coordinated with three nitrogen atoms and a methoxyl oxygen atom of two L ligands, and an acetonitrile. In [Cu(II)L(NO3)2]·CH3CN 2, the Cu(II) center is coordinated to the two nitrogen atoms of the two pyridine rings of L which acts as a bidentate ligand. The structures of [Ni(II)L(NO3)(H2O)2]·2CH3CN·NO3 (3), [Zn(II)L(NO3)2 (H2O)]·2CH3CN (4) and [Co(II)LCl2(H2O)] (5) are similar to each other in which L acts as a tridentate ligand by using its half side, and the metal centers are coordinated to a methoxyl oxygen atom and two bipyridine nitrogen atoms of L in the same side. The formation of infinite quasi-one-dimensional chains (1, 4 and 5) or a quasi-two-dimensional sheet (2) assisted by the intra- or intermolecular face-to-face aryl stacking interactions and hydrogen bonds may have stabilized the crystals of these complexes. Luminescence studies showed that 1 exhibits broad, structureless emissions at 420 nm in the solid state and at 450 nm in frozen alcohol frozen glasses at 77 K. Cyclic voltammetric studies of 1 show the presence of an irreversible metal-centered reduction wave at approximately −0.973 V versus Fc+/0 and a quasi-reversible ligand-centered reduction couple at approximately −1.996 V versus Fc+/0. The solution behaviors of these complexes have been further studied by UV-Vis and ESR techniques. 相似文献
942.
Molecular modeling of flavonoids that inhibits xanthine oxidase 总被引:8,自引:0,他引:8
Lin CM Chen CS Chen CT Liang YC Lin JK 《Biochemical and biophysical research communications》2002,294(1):167-172
The inhibition of xanthine oxidase activity by various flavonoids was assessed. All of the tested flavonoids were competitive inhibitors, and from the kinetic analysis suggested that flavonoids bind to the reactive site. To further understand the stereochemistry between these flavonoids and xanthine oxidase, structure-based molecular modeling was performed. Apigenin was the most potent inhibitor which showed the most favorable interaction in the reactive site. The bicyclic benzopyranone ring of apigenin stacked with phenyl of Phe 914, and the phenolic group stretched to the space surrounding with several hydrophobic residues. Quercetin and myricetin composed a 3-hydroxyl group on benzopyranone which resulting in reduction of binding affinity. The phenolic group of genistein positioned in opposite orientation comparison with apigenin, and resulted in a weaker interaction with xanthine oxidase. Isovitexin showed the weakest inhibitory effect among the compounds tested. The bulky group of sugar in isovitexin may hamper its interaction with xanthine oxidase. 相似文献
943.
Bing C Gomez-Ambrosi J Zabalegui N Williams G Trayhurn P 《Biochemical and biophysical research communications》2002,295(2):458-462
An ORF2 gene located upstream of the cellulose synthase (bcs) operon of Acetobacter xylinum BPR2001 was disrupted and a mutant (M2-2) was constructed. In static cultivation, the parent strain produced a tough, colorless, and insoluble cellulose pellicle, whereas M2-2 culture produced a thin, yellow, and fragile pellicle. The results of X-ray diffraction and 13C solid-state NMR indicated that the product of M2-2 is a mixture of cellulose I, cellulose II, and amorphous cellulose. The cellulose I to cellulose II ratio of the mixture was evaluated from the signal areas of C6 to be about 1:2. Electron microscopy revealed that the product of M2-2 included ribbon-like cellulose and irregularly shaped particles attached to the ribbons. On the other hand, the mutant complemented with plasmid pSA-ORF2/k containing the ORF2 gene and BPR2001 produced only cellulose I. These results indicate that the ORF2 gene is involved in the production and crystallization of cellulose I microfibrils by this microorganism. 相似文献
944.
Two blazeispirane derivatives including blazeispirols G and I were isolated from the cultured mycelia of the fungus Agaricus blazei Murill and were established to be (20S, 22S, 23R, 24S)-14 beta,22: 22,25-diepoxy-5-methoxy-des-A-ergosta-5,7,9-triene-11 alpha,23-diol and (20S, 22S, 23R, 24S)-14 beta,22:22,25-diepoxy-5-methoxy-des-A-ergosta-5,7,9,11-tetraene-23,28-diol by comparison of extensive 1D and 2D NMR spectral data with that of blazeispirol A. Furthermore, four blazeispirol derivatives blazeispirols, U, V, V(1) and Z(1) were isolated form the same source described above. Their structures were determined to be (20S, 22S, 23R, 24S)-14 beta,22:22,25-diepoxy-23-hydroxyergosta-4,6,8,11-tetraen-3-one, (20S, 22S, 23R, 24S)-14 beta,22:22,25-diepoxy-6 alpha,7 alpha,23-trihydroxyergosta-4,8,11-trien-3-one, (20S, 22S, 23R, 24S)-14 beta,22:22,25-diepoxy-6 beta,7 alpha,23-trihydroxyergosta-4,8,11-trien-3-one and (20S, 22S, 23R, 24S)-14 beta,22:22,25-diepoxy-23-hydroxy-4,5-seco-ergosta-6,8-diene-3,5-dione by extensive 1 D and 2D NMR spectral data. 相似文献
945.
946.
Price BM Barten Legutki J Galloway DR von Specht BU Gilleland LB Gilleland HE Staczek J 《FEMS immunology and medical microbiology》2002,33(2):89-99
The outer membrane protein F gene (oprF) of Pseudomonas aeruginosa was recently shown by us to protect mice from P. aeruginosa chronic pulmonary infection when used as a DNA vaccine administered by three biolistic (gene gun) intradermal inoculations given at 2-week intervals. In the present study, we used two different strategies to improve the protective efficacy of the DNA vaccine. In the first strategy, mice were primed with two biolistic intradermal inoculations with the oprF vaccine and then were given a final intramuscular booster immunization containing either a synthetic peptide-keyhole limpet hemocyanin (KLH) conjugate or a chimeric influenza virus. Both the synthetic peptide conjugate and the chimeric virus contained peptide 10, a previously identified immunoprotective epitope of protein F. The second strategy involved the addition of a second outer membrane protein to the vaccine. DNA encoding a fusion protein comprised of the C-terminal half of protein F fused to OprI was administered by three biolistic intradermal inoculations. Challenge with P. aeruginosa in a chronic pulmonary infection model demonstrated that boosting with the chimeric virus (but not with peptide-KLH) or adding oprI to the DNA vaccine significantly enhanced protection as compared to that afforded by the oprF vaccine given alone. Thus, both strategies appear to augment the protection afforded by an oprF-only DNA vaccine. 相似文献
947.
Lipid peroxidation in cotton: Xanthomonas interactions and the role of lipoxygenases during the hypersensitive reaction 总被引:12,自引:0,他引:12
948.
The absence of molybdenum cofactor sulfuration is the primary cause of the flacca phenotype in tomato plants 总被引:1,自引:0,他引:1
The molybdenum cofactor (MoCo)-containing enzymes aldehyde oxidase (AO; EC 1.2.3.1) and xanthine dehydrogenase (XDH; EC 1.2.1.37) require for activity a sulfuration step that inserts a terminal sulfur ligand into the MoCo. The tomato flacca mutation was originally isolated as a wilty phenotype due to a lack of abscisic acid (ABA) that is related to simultaneous loss of AO and XDH activities. An expressed sequence tag candidate from tomato was selected on the basis of homology to sulfurases from animals, fungi and the recently isolated Arabidopsis genes LOS5/ABA3. The tomato homologue maps as a single gene to the bottom of chromosome 7, consistent with the genetic location of the flacca mutation. The structure of FLACCA shows a multidomain protein with an N-terminal NifS-like sulfurase domain; a mammal-specific intermediate section; and a C-terminus containing conserved motifs. Prominent among these are molybdopterin oxidoreductases and thioredoxin redox-active centre/iron-sulfur-binding region signatures which may be relevant to the specific sulfuration of MoCo. Indeed, the molecular analysis of flacca identifies the mutation in a highly conserved motif located in the C-terminus. Activity gel assays show that FLACCA is expressed throughout the plant. Transient and stable complementation of flacca and the Arabidopsis aba3 mutants with Aspergillus nidulans hxB and FLACCA yielded full, partial and tissue-specific types of Mo-hydroxylase activities. Restoration of activity in the root alone is sufficient to augment plant ABA content and rectify the wild-type phenotype. Thus the pleiotropic flacca phenotype is due to the loss of activity of enzymes requiring a sulfurated MoCo. 相似文献
949.
Quantitation of GFP-fusion proteins in single living cells 总被引:9,自引:0,他引:9
950.