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991.
In acetate buffer, pH 4, at room temperature, nitrite ions can mediate an unusual decarboxylative conjugation of caffeic acid with glutathione leading to novel isomeric 2-(3,4-dihydroxyphenyl)-2-S-glutathionylacetaldehyde oximes. These results hint at a possible role of endogenous and/or dietary glutathione in the mechanisms by which caffeic acid can affect the burden of carcinogenic N-nitroso compounds in the digestive tract. 相似文献
992.
The solution structure of human beta2-microglobulin reveals the prodromes of its amyloid transition 下载免费PDF全文
Verdone G Corazza A Viglino P Pettirossi F Giorgetti S Mangione P Andreola A Stoppini M Bellotti V Esposito G 《Protein science : a publication of the Protein Society》2002,11(3):487-499
The solution structure of human beta2-microglobulin (beta2-m), the nonpolymorphic component of class I major histocompatibility complex (MHC-I), was determined by (1)H NMR spectroscopy and restrained modeling calculations. Compared to previous structural data obtained from the NMR secondary structure of the isolated protein and the crystal structure of MHC-I, in which the protein is associated to the heavy-chain component, several differences are observed. The most important rearrangements were observed for (1) strands V and VI (loss of the C-terminal and N-terminal end, respectively), (2) interstrand loop V-VI, and (3) strand I, including the N-terminal segment (displacement outward of the molecular core). These modifications can be considered as the prodromes of the amyloid transition. Solvation of the protected regions in MHC-I decreases the tertiary packing by breaking the contiguity of the surface hydrophobic patches at the interface with heavy chain and the nearby region at the surface charge cluster of the C-terminal segment. As a result, the molecule is placed in a state in which even minor charge and solvation changes in response to pH or ionic-strength variations can easily compromise the hydrophobic/hydrophilic balance and trigger the transition into a partially unfolded intermediate that starts with unpairing of strand I and leads to polymerization and precipitation into fibrils or amorphous aggregates. The same mechanism accounts for the partial unfolding and fiber formation subsequent to Cu(2+) binding, which is shown to occur primarily at His 31 and involve partially also His 13, the next available His residue along the partial unfolding pathway. 相似文献
993.
994.
Cell cycle-dependent dynamic association of cyclin/Cdk complexes with human DNA replication proteins
Frouin I Montecucco A Biamonti G Hübscher U Spadari S Maga G 《The EMBO journal》2002,21(10):2485-2495
We have previously described the isolation of a replication competent (RC) complex from calf thymus, containing DNA polymerase alpha, DNA polymerase delta and replication factor C. Here, we describe the isolation of the RC complex from nuclear extracts of synchronized HeLa cells, which contains DNA replication proteins associated with cell-cycle regulation factors like cyclin A, cyclin B1, Cdk2 and Cdk1. In addition, it contains a kinase activity and DNA polymerase activities able to switch from a distributive to a processive mode of DNA synthesis, which is dependent on proliferating cell nuclear antigen. In vivo cross-linking of proteins to DNA in synchronized HeLa cells demonstrates the association of this complex to chromatin. We show a dynamic association of cyclins/Cdks with the RC complex during the cell cycle. Indeed, cyclin A and Cdk2 associated with the complex in S phase, and cyclin B1 and Cdk1 were present exclusively in G(2)/M phase, suggesting that the activity, as well the localization, of the RC complex might be regulated by specific cyclin/Cdk complexes. 相似文献
995.
Detection and localization of pectin methylesterase isoforms in pollen tubes of Nicotiana tabacum L. 总被引:7,自引:0,他引:7
Pectin methylesterases (PMEs) were detected in tobacco ( Nicotiana tabacum) pollen tubes grown in vitro. Seven PME isoforms exhibiting a wide isoelectric-point (pI) range (5.3-9.1) were found in crude extracts of pollen tubes. These isoforms were mainly retrieved in supernatants after low- and high-speed separation of the crude extract. Two isoforms, with pIs 5.5 and 7.3 and molecular weight about 158 kDa, were detected by immunoblotting with anti-flax PME antiserum. Localization of pectins and PME isoforms in pollen tubes was investigated by immunogold labelling with JIM5 monoclonal antibodies and anti-flax PME antiserum, respectively. In germinated pollen grains, two PME isoforms were mainly detected in the exine, Golgi apparatus and secretory vesicles. In pollen tubes the same two PME isoforms were distributed along the outer face of the plasma membrane in the vicinity of the inner layer of the cell wall, in the Golgi and around secretory vesicles. In pollen grains, PME isoforms were, in some cases, mixed with acidic pectins in proximity to the outer surface of the plasma membrane. In pollen tubes the presence of PMEs inside secretory vesicles carrying esterified pectins supports the hypothesis that, during pollen tube growth, PMEs could be transferred by secretory vesicles in a precursor form and be activated at the tip where exocytosis takes place. 相似文献
996.
Tiberio R Marconi A Fila C Fumelli C Pignatti M Krajewski S Giannetti A Reed JC Pincelli C 《FEBS letters》2002,520(1-3):139-144
In zebrafish, the basic helix-loop-helix (bHLH) gene neuroD specifies distinct neurons in the spinal cord. A preliminary experiment indicated that a related bHLH gene, ndr1a, normally expressed only in the olfactory organ in late embryos, also functions as neuroD to induce ectopic formation of spinal cord neurons in early embryos after introduction of its mRNA into early embryos. To define the functional specificity of these bHLH proteins, several mutant forms with selected point mutations in the basic domain were constructed and tested for inducing sensory neurons in the spinal cord. Our data indicate that the functional specificity of NeuroD to define sensory neurons is mainly due to a single residue (asparagine 11) in its basic domain. 相似文献
997.
Human telomeric position effect is determined by chromosomal context and telomeric chromatin integrity 总被引:7,自引:0,他引:7 下载免费PDF全文
Koering CE Pollice A Zibella MP Bauwens S Puisieux A Brunori M Brun C Martins L Sabatier L Pulitzer JF Gilson E 《EMBO reports》2002,3(11):1055-1061
We investigated the influence of telomere proximity and composition on the expression of an EGFP reporter gene in human cells. In transient transfection assays, telomeric DNA does not repress EGFP but rather slightly increases its expression. In contrast, in stable cell lines, the same reporter construct is repressed when inserted at a subtelomeric location. The telomeric repression is transiently alleviated by increasing the dosage of the TTAGGG repeat factor 1 (TRF1). Upon a prolongated treatment with trichostatin A, the derepression of the subtelomeric reporter gene correlates with the delocalization of HP1α and HP1β. In contrast, treating the cells with 5 azacytidin, a demethylating agent, or with sirtinol, an inhibitor of the Sir2 family of deacetylase, has no apparent effect on telomeric repression. Overall, position effects at human chromosome ends are dependent on a specific higher-order organization of the telomeric chromatin. The possible involvement of HP1 isoforms is discussed. 相似文献
998.
Pesce A Bolognesi M Bocedi A Ascenzi P Dewilde S Moens L Hankeln T Burmester T 《EMBO reports》2002,3(12):1146-1151
Neuroglobin and cytoglobin are two recently discovered members of the vertebrate globin family. Both are intracellular proteins endowed with hexacoordinated heme-Fe atoms, in their ferrous and ferric forms, and display O2 affinities comparable with that of myoglobin. Neuroglobin, which is predominantly expressed in nerve cells, is thought to protect neurons from hypoxic–ischemic injury. It is of ancient evolutionary origin, and is homologous to nerve globins of invertebrates. Cytoglobin is expressed in many different tissues, although at varying levels. It shares common ancestry with myoglobin, and can be traced to early vertebrate evolution. The physiological roles of neuroglobin and cytoglobin are not completely understood. Although supplying cells with O2 is the likely function, it is also possible that both globins act as O2-consuming enzymes or as O2 sensors. Here, we review what is currently known about neuroglobin and cytoglobin in terms of their function, tissue distribution and relatedness to the well-known hemoglobin and myoglobin. Strikingly, the data reveal that O2 metabolism in cells is more complicated than was thought before, requiring unexpected O2-binding proteins with potentially novel functional features. 相似文献
999.
1000.
Separation of carbamazepine and five metabolites,and analysis in human plasma by micellar electrokinetic capillary chromatography 总被引:1,自引:0,他引:1
Raggi MA Pucci V Maurizio A Muzikar J Kenndler E 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2002,770(1-2):217-225
A rapid and feasible method was developed for the analysis of carbamazepine and its five metabolites (10,11-dihydro-10,11-epoxycarbamazepine, 10,11-dihydro-10,11-dihydroxycarbamazepine, 10,11-dihydro-10-hydroxycarbamazepine, 2-hydroxycarbamazepine and 3-hydroxycarbamazepine) in human plasma. Separation of the analytes is based on micellar electrokinetic chromatography, in untreated fused-silica capillary (48.5/40.0 cm length, 50 microm I.D.) with phosphate buffer (30 mM, pH 8.00) as background electrolyte, containing 50 mM sodium dodecylsulfate, and methanol (15%, v/v) as organic modifier. Clean up of human plasma samples was carried out by means of a solid-phase extraction procedure, which gave a high extraction yield for all six carbamazepines (>88%). The overall precision of the method gives a mean RSD of about 1.8%. The limit of quantitation for all analytes is < or = 0.30 microg ml(-1), the limit of detection < or = 0.12 microg ml(-1). 相似文献