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931.
Cyclometalation of benzo[h]quinoline (bzqH) by [RuCl(μ-Cl)(η6-C6H6)]2 in acetonitrile occurs in a similar way to that of 2-phenylpyridine (phpyH) to afford [Ru(bzq)(MeCN)4]PF6 (3) in 52% yield. The properties of 3 containing ‘non-flexible’ benzo[h]quinoline were compared with the corresponding [Ru(phpy)(MeCN)4]PF6 (1) complex with ‘flexible’ 2-phenylpyridine. The [Ru(phpy)(MeCN)4]PF6 complex is known to react in MeCN solvent with ‘non-flexible’ diimine 1,10-phenanthroline to form [Ru(phpy)(phen)(MeCN)2]PF6, being unreactive toward ‘flexible’ 2,2′-bipyridine under the same conditions. In contrast, complex 3 reacts both with phen and bpy in MeCN to form [Ru(bzq)(LL)(MeCN)2]PF6 {LL = bpy (4) and phen (5)}. Similar reaction of 3 in methanol results in the substitution of all four MeCN ligands to form [Ru(bzq)(LL)2]PF6 {LL = bpy (6) and phen (7)}. Photosolvolysis of 4 and 5 in MeOH occurs similarly to afford [Ru(bzq)(LL)(MeCN)(MeOH)]PF6 as a major product. This contrasts with the behavior of [Ru(phpy)(LL)(MeCN)2]PF6, which lose one and two MeCN ligands for LL = bpy and phen, respectively. The results reported demonstrate a profound sensitivity of properties of octahedral compounds to the flexibility of cyclometalated ligand. Analogous to the 2-phenylpyridine counterparts, compounds 4-7 are involved in the electron exchange with reduced active site of glucose oxidase from Aspergillus niger. Structure of complexes 4 and 6 was confirmed by X-ray crystallography. 相似文献
932.
Anna Katafias Author Vitae Janusz Chat?as Author Vitae Author Vitae Przemys?aw Kita Author Vitae Author Vitae Adrian Topolski Author Vitae Author Vitae Jette Eriksen Author Vitae Author Vitae Andrew Mills Author Vitae 《Inorganica chimica acta》2010,363(11):2346-2356
The review provides insight into the mechanism of ligand substitution and electron transfer (from chromium(III) to iron(III)) by comparison of the reactivity of some tetraazamacrocyclic chromium(III) complexes in the conjugate acid-base forms. Use of two geometrical isomers made possible to estimate the influence of geometry and protolytic reactions in trans and cis position towards the leaving group on the rate enhancement. Studies on the reaction rates in different media demonstrated the role played by outer sphere interactions in a monodentate ligand substitution. 相似文献
933.
Massimo Micaroni Giuseppe Perinetti Daniele Di Giandomenico Alexander Spaar 《Experimental cell research》2010,316(13):2071-2086
The mechanisms of secretory transport through the Golgi apparatus remain an issue of debate. The precise functional importance of calcium ions (Ca2+) for intra-Golgi transport has also been poorly studied. Here, using different approaches to measure free Ca2+ concentrations in the cell cytosol ([Ca2+]cyt) and inside the lumen of the Golgi apparatus ([Ca2+]GA), we have revealed transient increases in [Ca2+]cyt during the late phase of intra-Golgi transport that are concomitant with a decline in the maximal [Ca2+]GA restoration ability. Thus, this redistribution of Ca2+ from the Golgi apparatus into the cytosol during the movement of cargo through the Golgi apparatus appears to have a role in intra-Golgi transport, and mainly in the late Ca2+-dependent phase of SNARE-regulated fusion of Golgi compartments. 相似文献
934.
Lysosomal degradation of membrane lipids 总被引:1,自引:0,他引:1
Thomas Kolter 《FEBS letters》2010,584(9):1700-6422
The constitutive degradation of membrane components takes place in the acidic compartments of a cell, the endosomes and lysosomes. Sites of lipid degradation are intralysosomal membranes that are formed in endosomes, where the lipid composition is adjusted for degradation. Cholesterol is sorted out of the inner membranes, their content in bis(monoacylglycero)phosphate increases, and, most likely, sphingomyelin is degraded to ceramide. Together with endosomal and lysosomal lipid-binding proteins, the Niemann-Pick disease, type C2-protein, the GM2-activator, and the saposins sap-A, -B, -C, and -D, a suitable membrane lipid composition is required for degradation of complex lipids by hydrolytic enzymes. 相似文献
935.
Methylation of tRNA on the four canonical bases adds structural complexity to the molecule, and improves decoding specificity and efficiency. While many tRNA methylases are known, detailed insight into the catalytic mechanism is only available in a few cases. Of interest among all tRNA methylases is the structural basis for nucleotide selection, by which the specificity is limited to a single site, or broadened to multiple sites. General themes in catalysis include the basis for rate acceleration at highly diverse nucleophilic centers for methyl transfer, using S-adenosylmethionine as a cofactor. Studies of tRNA methylases have also yielded insights into molecular evolution, particularly in the case of enzymes that recognize distinct structures to perform identical reactions at the same target nucleotide. 相似文献
936.
Masaki Yoshida Nagakatsu Harada Tadahiko Nakagawa Kazuaki Mawatari Hiroshi Sakaue 《FEBS letters》2010,584(6):1217-1222
A link between cellular uptake of high density lipoprotein (HDL) and regulation of sterol regulatory element-binding protein-1 (SREBP-1) was investigated in vitro. HDL decreased nuclear SREBP-1 levels as well as SREBP-1 target gene expression in HepG2 and HEK293 cells. However, HDL did not repress an exogenously expressed, constitutively active form of SREBP-1. HDL increased cellular cholesterol levels, and cellular cholesterol depletion by methyl-β-cyclodextrin abolished the effects of HDL. These results suggest that HDL inhibits the activation of SREBP-1 through a cholesterol-dependent mechanism, which may play an important role in regulating lipid synthetic pathways mediated by SREBP-1. 相似文献
937.
A particular type of pentatricopeptide repeat (PPR) proteins with variable length of the 35 aa PPR motifs and conserved carboxyterminal extensions, named the PLS proteins, was so far exclusively identified in land plants. Several PLS proteins with such domain extensions (E, E+, DYW) were shown to be involved in plant organellar RNA editing but their evolutionary origin had remained enigmatic. We here report the first case of DYW-type PLS proteins outside of the plant kingdom in the protist Naegleria gruberi and hypothesize on horizontal gene transfer in very early land plant evolution. 相似文献
938.
Chronic diseases are associated with considerable morbidity and mortality. Therefore, new therapeutic strategies are warranted. Here, we provide a brief review outlining the rationale and feasibility for the generation of intraspecies and interspecies chimeras, which one day may serve as a platform for organ transplantation. These strategies are further associated with consideration of scientific and ethical issues. 相似文献
939.
Pyrococcus furiosus protease I (PFPI) is a multimeric cysteine peptidase from P. furiosus. Genome analyses indicate that orthologues are present in rather few other organisms, including Dictyostelium discoideum and several bacteria, Archaea and plants. An open reading frame (ORF) coding for a PFPI-like protein (PFP1) was identified in Leishmania major and Leishmania mexicana and full-length spliced and polyadenylated PFP1 mRNA detected for both species. Vestiges of a PFPI-like gene could also be identified in Leishmania braziliensis and Leishmania infantum, but no ORF remains owing to the presence of frame-shifts and stop codons. No evidence for a PFPI-like gene could be found in the syntenic region of Trypanosoma brucei or Trypanosoma cruzi, raising the possibility that the PFPI-like genes were acquired by a lateral gene transfer event after the divergence of trypanosomes and Leishmania. The gene may have subsequently degenerated into a pseudogene in some Leishmania species, owing to the loss of relevant biological function. However, antibodies raised against L. mexicana recombinant protein detected PFP1 in promastigote extracts of L. major, but not in L. mexicana promastigote or amastigote extracts. The expression of PFP1 in L. major suggests that PFP1 might contribute to the disease tropism that distinguishes this Leishmania species from others. 相似文献
940.
Christopher M. Finelli Brian S. T. Helmuth N. Dean Pentcheff David S. Wethey 《Coral reefs (Online)》2006,25(1):47-57
Recent studies indicate that the incidence and persistence of damage from coral reef bleaching are often highest in areas of restricted water motion, and that resistance to and recovery from bleaching is increased by enhanced water motion. We examined the hypothesis that water motion increases the efflux of oxygen from coral tissue thereby reducing oxidative stress on the photosynthetic apparatus of endosymbiotic zooxanthellae. We experimentally exposed colonies of Montastrea annularis and Agaricia agaricites to manipulations of water flow, light intensity, and oxygen concentration in the field using a novel mini-flume. We measured photosynthetic efficiency using a pulse amplitude modulated fluorometer to test the short-term response of corals to our manipulations. Under normal oxygen concentrations, A. agaricites showed a significant 8% increase in photosynthetic efficiency from 0.238 (± 0.032) in still water to 0.256 (± 0.037) in 15 cm s−1 flow, while M. annularis exhibited no detectable change. Under high-ambient oxygen concentrations, the observed effect of flow on A. agaricites was reversed: photosynthetic efficiencies showed a significant 11% decrease from 0.236 (± 0.056) in still water to 0.211 (± 0.048) in 15 cm s−1 flow. These results support the hypothesis that water motion helps to remove oxygen from coral tissues during periods of maximal photosynthesis. Flow mitigation of oxidative stress may at least partially explain the increased incidence and severity of coral bleaching in low flow areas and observations of enhanced recovery in high-flow areas. 相似文献