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排序方式: 共有551条查询结果,搜索用时 31 毫秒
61.
Boot KJ Libbenga KR Hille SC Offringa R van Duijn B 《Journal of experimental botany》2012,63(11):4213-4218
In higher plants, cell-to-cell polar auxin transport (PAT) of the phytohormone auxin, indole-3-acetic acid (IAA), generates maxima and minima that direct growth and development. Although IAA is present in all plant phyla, PAT has only been detected in land plants, the earliest being the Bryophytes. Charophyta, a group of freshwater green algae, are among the first multicellular algae with a land plant-like phenotype and are ancestors to land plants. IAA has been detected in members of Charophyta, but its developmental role and the occurrence of PAT are unknown. We show that naphthylphthalamic acid (NPA)-sensitive PAT occurs in internodal cells of Chara corallina. The relatively high velocity (at least 4-5 cm/h) of auxin transport through the giant (3-5 cm) Chara cells does not occur by simple diffusion and is not sensitive to a specific cytoplasmic streaming inhibitor. The results demonstrate that PAT evolved early in multicellular plant life. The giant Chara cells provide a unique new model system to study PAT, as Chara allows the combining of real-time measurements and mathematical modelling with molecular, developmental, cellular, and electrophysiological studies. 相似文献
62.
Lambeck IC Fischer-Schrader K Niks D Roeper J Chi JC Hille R Schwarz G 《The Journal of biological chemistry》2012,287(7):4562-4571
14-3-3 proteins regulate key processes in eukaryotic cells including nitrogen assimilation in plants by tuning the activity of nitrate reductase (NR), the first and rate-limiting enzyme in this pathway. The homodimeric NR harbors three cofactors, each of which is bound to separate domains, thus forming an electron transfer chain. 14-3-3 proteins inhibit NR by binding to a conserved phosphorylation site localized in the linker between the heme and molybdenum cofactor-containing domains. Here, we have investigated the molecular mechanism of 14-3-3-mediated NR inhibition using a fragment of the enzyme lacking the third domain, allowing us to analyze electron transfer from the heme cofactor via the molybdenum center to nitrate. The kinetic behavior of the inhibited Mo-heme fragment indicates that the principal point at which 14-3-3 acts is the electron transfer from the heme to the molybdenum cofactor. We demonstrate that this is not due to a perturbation of the reduction potentials of either the heme or the molybdenum center and conclude that 14-3-3 most likely inhibits nitrate reductase by inducing a conformational change that significantly increases the distance between the two redox-active sites. 相似文献
63.
Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) regulates activities of numerous ion channels including inwardly rectifying potassium (Kir) channels, KCNQ, TRP, and voltage-gated calcium channels. Several studies suggest that voltage-gated potassium (KV) channels might be regulated by PI(4,5)P2. Wide expression of KV channels in different cells suggests that such regulation could have broad physiological consequences. To study regulation of KV channels by PI(4,5)P2, we have coexpressed several of them in tsA-201 cells with a G protein–coupled receptor (M1R), a voltage-sensitive lipid 5-phosphatase (Dr-VSP), or an engineered fusion protein carrying both lipid 4-phosphatase and 5-phosphatase activity (pseudojanin). These tools deplete PI(4,5)P2 with application of muscarinic agonists, depolarization, or rapamycin, respectively. PI(4,5)P2 at the plasma membrane was monitored by Förster resonance energy transfer (FRET) from PH probes of PLCδ1 simultaneously with whole-cell recordings. Activation of Dr-VSP or recruitment of pseudojanin inhibited KV7.1, KV7.2/7.3, and Kir2.1 channel current by 90–95%. Activation of M1R inhibited KV7.2/7.3 current similarly. With these tools, we tested for potential PI(4,5)P2 regulation of activity of KV1.1/KVβ1.1, KV1.3, KV1.4, and KV1.5/KVβ1.3, KV2.1, KV3.4, KV4.2, KV4.3 (with different KChIPs and DPP6-s), and hERG/KCNE2. Interestingly, we found a substantial removal of inactivation for KV1.1/KVβ1.1 and KV3.4, resulting in up-regulation of current density upon activation of M1R but no changes in activity upon activating only VSP or pseudojanin. The other channels tested except possibly hERG showed no alteration in activity in any of the assays we used. In conclusion, a depletion of PI(4,5)P2 at the plasma membrane by enzymes does not seem to influence activity of most tested KV channels, whereas it does strongly inhibit members of the KV7 and Kir families. 相似文献
64.
Ilagan RP Tiso M Konas DW Hemann C Durra D Hille R Stuehr DJ 《The Journal of biological chemistry》2008,283(28):19603-19615
Nitric oxide (NO) is a physiological mediator synthesized by NO synthases (NOS). Despite their structural similarity, endothelial NOS (eNOS) has a 6-fold lower NO synthesis activity and 6-16-fold lower cytochrome c reductase activity than neuronal NOS (nNOS), implying significantly different electron transfer capacities. We utilized purified reductase domain constructs of either enzyme (bovine eNOSr and rat nNOSr) to investigate the following three mechanisms that may control their electron transfer: (i) the set point and control of a two-state conformational equilibrium of their FMN subdomains; (ii) the flavin midpoint reduction potentials; and (iii) the kinetics of NOSr-NADP+ interactions. Although eNOSr and nNOSr differed in their NADP(H) interaction and flavin thermodynamics, the differences were minor and unlikely to explain their distinct electron transfer activities. In contrast, calmodulin (CaM)-free eNOSr favored the FMN-shielded (electron-accepting) conformation over the FMN-deshielded (electron-donating) conformation to a much greater extent than did CaM-free nNOSr when the bound FMN cofactor was poised in each of its three possible oxidation states. NADPH binding only stabilized the FMN-shielded conformation of nNOSr, whereas CaM shifted both enzymes toward the FMN-deshielded conformation. Analysis of cytochrome c reduction rates measured within the first catalytic turnover revealed that the rate of conformational change to the FMN-deshielded state differed between eNOSr and nNOSr and was rate-limiting for either CaM-free enzyme. We conclude that the set point and regulation of the FMN conformational equilibrium differ markedly in eNOSr and nNOSr and can explain the lower electron transfer activity of eNOSr. 相似文献
65.
Xanthine oxidoreductase catalyzes the final two steps of purine catabolism and is involved in a variety of pathological states ranging from hyperuricemia to ischemia-reperfusion injury. The human enzyme is expressed primarily in its dehydrogenase form utilizing NAD+ as the final electron acceptor from the enzyme's flavin site but can exist as an oxidase that utilizes O2 for this purpose. Central to an understanding of the enzyme's function is knowledge of purine substrate orientation in the enzyme's molybdenum-containing active site. We report here the crystal structure of xanthine oxidase, trapped at the stage of a critical intermediate in the course of reaction with the slow substrate 2-hydroxy-6-methylpurine at 2.3A. This is the first crystal structure of a reaction intermediate with a purine substrate that is hydroxylated at its C8 position as is xanthine and confirms the structure predicted to occur in the course of the presently favored reaction mechanism. The structure also corroborates recent work suggesting that 2-hydroxy-6-methylpurine orients in the active site with its C2 carbonyl group interacting with Arg-880 and extends our hypothesis that xanthine binds opposite this orientation, with its C6 carbonyl positioned to interact with Arg-880 in stabilizing the MoV transition state. 相似文献
66.
Koitka M Höchel J Obst D Rottmann A Gieschen H Borchert HH 《Analytical biochemistry》2008,381(1):113-122
Establishing esterase assays allows the determination and comparison of esteratic activities of tissues of one organism and between organisms. We have developed a high-performance liquid chromatography (HPLC) assay for the determination of S-acetylthiocholine (ATC) and p-nitrophenyl acetate (NPA) hydrolyzing activities of rat serum esterases based on ion pair chromatography with on-line radiochemical and ultraviolet (UV) detection. ATC is a substrate for cholinesterases, whereas NPA is cleaved by a variety of esterases and other proteins (e.g., cholinesterases, paraoxonase, carboxylesterase, albumin). Both substrates were incubated, simultaneously or separately, with rat serum to explore potential interferences between the enzymatic hydrolyses of the compounds. The ratio of the peak area of the 14C-labeled substrates to the total peak area of the substrates and their corresponding cleavage products was compared with the UV quantitation of ATC and p-nitrophenolate (NP), the cleavage product of NPA, measured at 230 and 350 nm, respectively. The peak identity of ATC and NP was confirmed by electrospray ionization-tandem mass spectrometry (ESI-MS/MS). The reaction rates of the assays using one substrate or both, as well as using radiochemical or UV detection, were equal. Moreover, the correlation between rat serum volumes and reaction rates was shown for both substrates. In conclusion, one can (i) choose between the two detection methods reliably, (ii) take advantage of monitoring both substrate and product by using radiochemical detection, and (iii) combine both substrates to determine esterase activities in rat serum and probably other biological matrices. 相似文献
67.
Dual Role of GdmH in Producer Immunity and Secretion of the Staphylococcal Lantibiotics Gallidermin and Epidermin 总被引:2,自引:2,他引:0
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Matthias Hille Stefanie Kies Friedrich Gtz Andreas Peschel 《Applied microbiology》2001,67(3):1380-1383
The biosynthetic gene clusters of the staphylococcal lantibiotics epidermin and gallidermin are distinguished by the presence of the unique genes epiH and gdmH, respectively. They encode accessory factors for the ATP-binding cassette transporters that mediate secretion of the antimicrobial peptides. Here, we show that gdmH also contributes to immunity to gallidermin but not to nisin. gdmH alone affected susceptibility to gallidermin only moderately, but it led to a multiplication of the immunity level mediated by the FEG immunity genes when cloned together with the gdmT gene, suggesting a synergistic activity of the H and FEG systems. gdmH-related genes were identified in the genomes of several bacteria, indicating an involvement in further cellular functions. 相似文献
68.
Spassova Mariana I. Prins Theo W. Folkertsma Rolf T. Klein-Lankhorst René M. Hille Jacques Goldbach Rob W. Prins Marcel 《Molecular breeding : new strategies in plant improvement》2001,7(2):151-161
Tomato spotted wilt virus is an important threat to tomato production worldwide. A single dominant resistance gene locus, Sw5, originating from Lycopersicon peruvianum, has been identified and introgressed in cultivated tomato plants. Here we present the genomic organization of a 35 250 bp fragment of a BAC clone overlapping the Sw5 locus. Two highly homologous (95%) resistance gene candidates were identified within 40 kb of the CT220 marker. The genes, tentatively named Sw5-a and Sw5-b, encode proteins of 1245 and 1246 amino acids, respectively, and are members of the coiled-coil, nucleotide-binding-ARC, leucine-rich repeat group of resistance gene candidates. Promoter and terminator regions of the genes are also highly homologous. Both genes significantly resemble the tomato nematode and aphid resistance gene Mi and, to a lesser extent, Pseudomonas syringae resistance gene Prf. Transformation of Nicotiana tabacum cv. SR1 plants revealed that the Sw5-b gene, but not the Sw5-a gene, is necessary and sufficient for conferring resistance against tomato spotted wilt virus. 相似文献
69.
The Biology of CRISPR-Cas: Backward and Forward 总被引:1,自引:0,他引:1
Frank Hille Hagen Richter Shi Pey Wong Majda Bratovič Sarah Ressel Emmanuelle Charpentier 《Cell》2018,172(6):1239-1259
70.
Friedrich Hille 《Plant Systematics and Evolution》1868,18(3):92-96
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