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151.
Plastoquinol as a singlet oxygen scavenger in photosystem II 总被引:2,自引:0,他引:2
It has been found that in Chlamydomonas reinhardtii cells, under high-light stress, the level of reduced plastoquinone considerably increases while in the presence of pyrazolate, an inhibitor of plastoquinone and tocopherol biosynthesis, the content of reduced plastoquinone quickly decreases, similarly to alpha-tocopherol. In relation to chlorophyll, after 18 h of growth under low light with the inhibitor, the content of alpha-tocopherol was 22.2 mol/1000 mol chlorophyll and that of total plastoquinone (oxidized and reduced) was 19 mol/1000 mol chlorophyll, while after 2 h of high-light stress the corresponding amounts dropped to 6.4 and 6.2 mol/1000 mol chlorophyll for alpha-tocopherol and total plastoquinone, respectively. The degradation of both prenyllipids was partially reversed by diphenylamine, a singlet oxygen scavenger. It was concluded that plastoquinol, as well as alpha-tocopherol is decomposed under high-light stress as a result of a scavenging reaction of singlet oxygen generated in photosystem II. The levels of both alpha-tocopherol and of the reduced plastoquinone are not affected significantly in the absence of the inhibitor due to a high turnover rate of both prenyllipids, i.e., their degradation is compensated by fast biosynthesis. The calculated turnover rates under high-light conditions were twofold higher for total plastoquinone (0.23 nmol/h/ml of cell culture) than for alpha-tocopherol (0.11 nmol/h/ml). We have also found that the level of alpha-tocopherolquinone, an oxidation product of alpha-tocopherol, increases as the alpha-tocopherol is consumed. The same correlation was also observed for gamma-tocopherol and its quinone form. Moreover, in the presence of pyrazolate under low-light growth conditions, the synthesis of plastoquinone-C, a hydroxylated plastoquinone derivative, was stimulated in contrast to plastoquinone, indicating for the first time a functional role for plastoquinone-C. The presented data also suggest that the two plastoquinones may have different biosynthetic pathways in C. reinhardtii. 相似文献
152.
153.
Schlapbach A Feifel R Hawtin S Heng R Koch G Moebitz H Revesz L Scheufler C Velcicky J Waelchli R Huppertz C 《Bioorganic & medicinal chemistry letters》2008,18(23):6142-6146
Pyrrolo-pyrimidones of the general structure 1 were synthesized and evaluated for their potential as MK2 inhibitors. Potent derivatives were discovered which inhibit MK2 in the nanomolar range and show potent inhibition of cytokine release from LPS-stimulated monocytes. These derivatives were shown to inhibit phosphorylation of hsp27, a downstream target of MK2 and are modestly selective in a panel of 28 kinases. 相似文献
154.
Bickmeyer U Grube A Klings KW Köck M 《Biochemical and biophysical research communications》2008,373(3):419-422
The alkaloid ageladine A, a pyrrole-imidazole alkaloid isolated from marine Agelas sponges shows fluorescence in the blue-green range during excitation with UV light with the highest absorption at 370 nm. The fluorescence of this alkaloid is pH dependent. Highest fluorescence is observed at pH 4, lowest at pH 9 with the largest fluorescence changes between pH 6 and 7. Ageladine A is brominated, which facilitates membrane permeation and therefore allows for easy staining of living cells and even whole transparent animal staining. To calculate the exact pH in solutions, cells, and tissues, the actual concentration of the alkaloid has to be known. A ratiometric measurement at the commonly used excitation wavelengths at 340/380 nm allows pH measurements in living tissues with an attenuated influence of the ageladine A concentration on calculated values. The fluorescence changes report small intracellular pH changes induced by extracellular acidification and alkalization as well as intracellular alkalization induced by ammonium chloride. 相似文献
155.
Achim Hoerauf Rolf D. Walter Hans Remme Janis Lazdins Bernhard Fleischer 《Trends in parasitology》2001,17(12):860-567
The Bernhard Nocht Institute for Tropical Medicine and the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases held an international conference to review recent achievements in research and control of onchocerciasis and lymphatic filariasis on 19-23 September 2001 in Hamburg, Germany. 相似文献
156.
Simone Biel J?rg Simon Roland Gross Teresa Ruiz Maarten Ruitenberg Achim Kr?ger 《European journal of biochemistry》2002,269(7):1974-1983
Hydrogenase and fumarate reductase isolated from Wolinella succinogenes were incorporated into liposomes containing menaquinone. The two enzymes were found to be oriented solely to the outside of the resulting proteoliposomes. The proteoliposomes catalyzed fumarate reduction by H2 which generated an electrical proton potential (Delta(psi) = 0.19 V, negative inside) in the same direction as that generated by fumarate respiration in cells of W. succinogenes. The H+/e ratio brought about by fumarate reduction with H2 in proteoliposomes in the presence of valinomycin and external K+ was approximately 1. The same Delta(psi) and H+/e ratio was associated with the reduction of 2,3-dimethyl-1,4-naphthoquinone (DMN) by H2 in proteoliposomes containing menaquinone and hydrogenase with or without fumarate reductase. Proteoliposomes containing menaquinone and fumarate reductase with or without hydrogenase catalyzed fumarate reduction by DMNH2 which did not generate a Delta(psi). Incorporation of formate dehydrogenase together with fumarate reductase and menaquinone resulted in proteoliposomes catalyzing the reduction of fumarate or DMN by formate. Both reactions generated a Delta(psi) of 0.13 V (negative inside). The H+/e ratio of formate oxidation by menaquinone or DMN was close to 1. The results demonstrate for the first time that coupled fumarate respiration can be restored in liposomes using the well characterized electron transport enzymes isolated from W. succinogenes. The results support the view that Delta(psi) generation is coupled to menaquinone reduction by H2 or formate, but not to menaquinol oxidation by fumarate. Delta(psi) generation is probably caused by proton uptake from the cytoplasmic side of the membrane during menaquinone reduction, and by the coupled release of protons from H2 or formate oxidation on the periplasmic side. This mechanism is supported by the properties of two hydrogenase mutants of W. succinogenes which indicate that the site of quinone reduction is close to the cytoplasmic surface of the membrane. 相似文献
157.
Helmut Haas Karl-Heinz Herzig Sabine André Jürgen Galle Achim Gronow Hans-Joachim Gabius 《Glycoconjugate journal》2001,18(4):273-275
Native Phaseolus vulgaris agglutinin (PHA) poses a potential health threat, when ingested with improperly cooked red kidney beans. Since PHA triggers human basophilic granulocytes in culture to rapidly release considerable amounts of interleukin-(IL-)4 and IL-13, key cytokines for inducing immunoglobulin E (IgE) production, the question was addressed whether this lectin can evoke in vivo IgE production. IgE-low-responder (Sprague-Dawley) rats received PHA (6 mg/rat/day) intragastrically by gavage over a period of 10 days. Up to day 35, there was no IgE induction regardless of whether the animals were boostered subcutaneously with PHA or not, indicating that PHA cannot be regarded as a general IgE inducer in rats. 相似文献
158.
Metal clusters are ubiquitously used as electron-transfer (ET) agents in biology. Their presence raises the question of how
the polynuclear nature of these systems influences ET. In an earlier study, a theoretical model was formulated to describe
ET from a mixed-valence dimer to a diamagnetic acceptor. In the present work, this approach is generalized to analyze the
effect of valence delocalization on the rate of ET in a larger class of donor–acceptor systems. Our results indicate that
the effect of valence delocalization on ET rate depends on whether the mixed-valence (MV) state occurs in the initial or final
state of the reaction and on the reaction regime (normal vs inverted) as defined by Marcus. The analysis provides a possible
correlation between the rate constant for ET from CuA to heme a and the difference in the valence delocalization of the CuA centers in wild-type and mutant species of cytochrome c oxidase. We have analyzed the dependence of the electron flow through extended circuits containing MV clusters on valence
delocalization. A significant effect was found in the fast ET regime where the capacity of the circuit to conduct electrons
is optimally used. The possibility of controlling electron conduction by tuning valence delocalization is briefly addressed.
Received: 16 July 1997 / Accepted: 26 November 1997 相似文献
159.
Karin Schuster-Gossler Ralf Cordes Julia Müller Insa Geffers Patricia Delany-Heiken Manuel Taft Matthias Preller Achim Gossler 《Genetics》2016,202(3):1119-1133
The highly conserved Notch-signaling pathway mediates cell-to-cell communication and is pivotal for multiple developmental processes and tissue homeostasis in adult organisms. Notch receptors and their ligands are transmembrane proteins with multiple epidermal-growth-factor-like (EGF) repeats in their extracellular domains. In vitro the EGF repeats of mammalian ligands that are essential for Notch activation have been defined. However, in vivo the significance of the structural integrity of each EGF repeat in the ligand ectodomain for ligand function is still unclear. Here, we analyzed the mouse Notch ligand DLL1. We expressed DLL1 proteins with mutations disrupting disulfide bridges in each individual EGF repeat from single-copy transgenes in the HPRT locus of embryonic stem cells. In Notch transactivation assays all mutations impinged on DLL1 function and affected both NOTCH1 and NOTCH2 receptors similarly. An allelic series in mice that carried the same point mutations in endogenous Dll1, generated using a mini-gene strategy, showed that early developmental processes depending on DLL1-mediated NOTCH activation were differently sensitive to mutation of individual EGF repeats in DLL1. Notably, some mutations affected only somite patterning and resulted in vertebral column defects resembling spondylocostal dysostosis. In conclusion, the structural integrity of each individual EGF repeat in the extracellular domain of DLL1 is necessary for full DLL1 activity, and certain mutations in Dll1 might contribute to spondylocostal dysostosis in humans. 相似文献
160.
Stuhr Marleen Meyer Achim Reymond Claire E. Narayan Gita R. Rieder Vera Rahnenführer Jörg Kucera Michal Westphal Hildegard Muhando Christopher A. Hallock Pamela 《Coral reefs (Online)》2018,37(3):811-824
Coral Reefs - Adaptation, acclimatization and symbiont diversity are known to regulate thermal tolerance in corals, but the role of these mechanisms remains poorly constrained in other... 相似文献