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61.
Carbon : nitrogen : phosphorus (C : N : P) stoichiometry can underlie physiological and life history characteristics that shape ecological interactions. Despite its potential importance, there is much to learn about the causes and consequences of stoichiometric variation in terrestrial consumers. Here we show that treehoppers (Publilia modesta) tended by ants (Formica obscuripes) contained lower N concentrations than treehoppers on plants from which ants were excluded. Ant presence also affected nutrient concentrations in host plants: on plants with ants, leaves contained uniformly low concentrations of N; on plants without ants, N concentrations were low only in the few leaves fed upon by treehoppers at the time of collection. We suggest treehopper feeding reduces leaf nutrient levels and ants positively affect treehopper abundance, producing a top–down effect on plant quality. Determining the causes of these stoichiometric changes should help elucidate factors guiding the dynamics of conditional mutualisms between ants and homopterans. 相似文献
62.
Sara Divari Francesca Valetti Patrizia Caposio Enrica Pessione Maria Cavaletto Ersilia Griva Giorgio Gribaudo Gianfranco Gilardi Carlo Giunta 《European journal of biochemistry》2003,270(10):2244-2253
Phenol hydroxylase (PH) from Acinetobacter radioresistens S13 represents an example of multicomponent aromatic ring monooxygenase made up of three moieties: a reductase (PHR), an oxygenase (PHO) and a regulative component (PHI). The function of the oxygenase component (PHO), here characterized for the first time, is to bind molecular oxygen and catalyse the mono-hydroxylation of substrates (phenol, and with less efficiency, chloro- and methyl-phenol and naphthol). PHO was purified from extracts of A. radioresistens S13 cells and shown to be a dimer of 206 kDa. Each monomer is composed by three subunits: alpha (54 kDa), beta (38 kDa) and gamma (11 kDa). The gene encoding PHO alpha (named mopN) was cloned and sequenced and the corresponding amino acid sequence matched with that of functionally related oxygenases. By structural alignment with the catalytic subunits of methane monooxygenase (MMO) and alkene monooxygenase, we propose that PHO alpha contains the enzyme active site, harbouring a dinuclear iron centre Fe-O-Fe, as also suggested by spectral analysis. Conserved hydrophobic amino acids known to define the substrate recognition pocket, are also present in the alpha-subunit. The prevalence of alpha-helices (99.6%) as studied by CD confirmed the hypothized structural homologies between PHO and MMO. Three parameters (optimum ionic strength, temperature and pH) that affect kinetics of the overall phenol hydroxylase reaction were further analyzed with a fixed optimal PHR/PHI/PHO ratio of 2/1/1. The highest level of activity was evaluated between 0.075 and 0.1 m of ionic strength, the temperature dependence showed a maximum of activity at 24 degrees C and finally the pH for optimal activity was determined to be 7.5. 相似文献
63.
Mei-Ling Siu-Caldera Jeffrey W. Clark Anabela Santos-Moore Sara Peleg Yan Yun Liu Milan R. Uskokovi Surendra Sharma G. Satyanarayana Reddy 《The Journal of steroid biochemistry and molecular biology》1996,59(5-6)
1α,25(OH)2-16-ene-D3, a synthetic analog of the steroid hormone, 1α,25(OH)2D3, has great potential to become a drug in the treatment of leukemia and other proliferative disorders, because of its minimal in vivo calcemic activity associated with a potent inhibitory effect on cell growth. However, at present, the mechanisms through which 1α,25(OH)2-16-ene-D3 expresses its biological activities are still not completely understood. Our previous in vitro study in a perfused rat kidney indicated for the first time that 1α,25(OH)2-16-ene-D3 and 1α,25(OH)2D3 are metabolized differently. 1α,25(OH)2-24-oxo-16-ene-D3, an intermediary metabolite of 1α,25(OH)2-16-ene-D3 formed through the C-24 oxidation pathway, accumulated significantly in the perfusate when compared to 1α,25(OH)2-24-oxo-D3, the corresponding intermediary metabolite of 1α,25(OH)2D3. In a subsequent in vivo study, we also reported that 1α,25(OH)2-24-oxo-16-ene-D3 exerted immunosuppressive activity equal to its parent, without causing significant hypercalcemia. In order to establish further the critical role of 1α,25(OH)2-24-oxo-16-ene-D3, in generating some of the key biological activities ascribed to its parent, we performed the present in vitro study using a human myeloid leukemic cell line (RWLeu-4) as a model. Comparative target tissue metabolism studies indicated that 1α,25(OH)2-16-ene-D3 and 1α,25(OH)2D3 are metabolized differently in RWLeu-4 cells, and the differences were similar to the ones we previously observed in the rat kidney. The significant finding was the accumulation of 1α,25(OH)2-24-oxo-16-ene-D3 in RWLeu-4 cells because of its resistance to further metabolism. Biological activity studies indicated that both 1α,25(OH)2-16-ene-D3 and its 24-oxo metabolite produced growth inhibition and promoted differentiation of RWLeu-4 cells to the same extent, and these activities were several fold higher than those exerted by 1α,25(OH)2D3. In addition, the genomic action of each vitamin D compound was assessed in a rat osteosarcoma cell line (ROS 17/2.8) by measuring its ability to transactivate a gene construct containing the vitamin D response element of the osteocalcin gene linked to the growth hormone reporter gene. In these studies, both 1α,25(OH)2-16-ene-D3 and its 24-oxo metabolite exerted similar but potent transactivation activity which was several fold greater than that exerted by 1α,25(OH)2D3 itself. In summary, our results indicate that the production and slow clearance of the bioactive intermediary metabolite, 1α,25(OH)2-24-oxo-16-ene-D3, in RWLeu-4 cells contributes significantly to the final expression of the enhanced biological activities ascribed to its parent analog, 1α,25(OH)2-16-ene-D3. 相似文献
64.
65.
Tsui-Ling C. Hsu Daniel S. Engebretson Sara A. Helvoigt Daniel G. Nocera 《Inorganica chimica acta》1995,240(1-2):551-557
The quadruple metal-metal bonded complexes, W2Cl4(PR3)4 (PR3 = PMe3, PMe2Ph, PBu3), photoreact in dichloromethane with near-UV excitation (λ>375 nm) to yield a mixed valence W2(II,III) photoproduct. Electronic absorption and EPR spectra of photolyzed solutions are identical to those obtained from the thermal oxidation of W2Cl4(PR3)4 by PhICI2, which is known to yield W2Cl5(PR3)3. Subsequent reaction of the photolyzed solution yields the oxidized, confacial biotahedral W2(III,III) halophosphine. Analysis of the organic photoproduct reveals that the halocarbon solvent is reduced by one electron to yield the chloromethyl radical. When the radical is produced in low yields, hydrogen abstraction from solvent appears to be sufficiently efficient to compete with dimerization and only chloromethane is observed; however, at higher concentrations, the chloromethyl radicals couple to produce dichloroethane. Photoreaction is observed only with near-UV excitation of the LMCT absorption manifold of W2Cl4(PR3)4. At lower energy wavelengths, transient absorption spectroscopy shows the production of the 1δδ* excited state, which decays to ground state over times commensurate with the decay of 1δδ* luminescence. In hydrocarbon solutions, no transient intermediate or photochemistry is observed, indicating that the LMCT excited state, although capable of reducing a C---X bond, cannot activate the stronger C---H bonds of hydrocarbons. The photochemistry and transient absorption spectroscopy results of the W2Cl4(PR3)4 complexes are compared to our previous studies of the
homologs. 相似文献
66.
Reproductive female 15-spined sticklebacks Spinachia spinachia chose water flowing from an unmated nesting male rather than water flowing from no male. Since the female could see neither the male nor his nest, this result suggests that she received non-visual signals. 相似文献
67.
Sujoy Ghosh John W. Kyle Sara Dastgheib Francois Daussin Zhixiong Li Subhash Basu 《Glycoconjugate journal》1995,12(6):838-847
A 1-3 galactosyltransferase (GalT-3; UDP-Gal; GM2 1-3galactosyltransferase) was purified over 5100-fold from 19-day-old embryonic chicken brain homogenate employing detergent solubilization, -lactalbumin Sepharose, Q-Sepharose, UDP-hexanolamine Sepharose, and GalNAc1-4Gal-Synsorb column chromatography. The purified enzyme was resolved into two bands on reducing gels with apparent molecular weights of 62 kDa and 65 kDa, respectively. GalT-3 activity was also localized in the same regions by activity gel analysis and sucrose-density gradient centrifugation of a detergent-solubilized extract of 19-day-old embryonic chicken brain. Purified GalT-3 exhibited apparentK
mS of 33 µm, 22 µm and 14.4mM with respect to the substrates GM2, UDP-galactose, and MnCl2, respectively. Substrate specificity studies with the purified enzyme and a variety of glycosphingolipids, glycoproteins, and synthetic substrates revealed that the enzyme was highly specific only for the glycosphingolipid acceptors, GM2 and GgOse3Cer (asialo-GM2). Ovine-asialo-agalacto submaxillary mucin inhibited the transfer of galactose to GM2 but did not act as an acceptor in the range of concentrations tested. Polyclonal antibodies raised against purified GalT-3 inhibited GalT-3 activityin vitro and Western-immunoblot analysis of purified GalT-3 showed immunopositive bands at 62 and 65 kDa.Abbreviations CNS
central nervous system
- GM1
monosialotetraosylganglioside, Gal1-3GalNAc1-4(NeuAc2-3)Gal1-4Glc1-1Cer
- GM2
monosialotriaosylganglioside, GalNAc1-4(NeuAc2-3)Gal1-4Glc1-1Cer
- DSS
detergent solubilized supernatant
- ECB
embryonic chicken brain
- TBS
Tris-buffered saline 相似文献
68.
Interleukin 1β-converting Enzyme Related Proteases/Caspases Are Involved in TRAIL-induced Apoptosis of Myeloma and Leukemia Cells
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Sara M. Mariani Bernd Matiba Elena A. Armandola Peter H. Krammer 《The Journal of cell biology》1997,137(1):221-229
The Fas/APO-1/CD95 ligand (CD95L) and the recently cloned TRAIL ligand belong to the TNFfamily and share the ability to induce apoptosis in sensitive target cells. Little information is available on the degree of functional redundancy between these two ligands in terms of target selectivity and intracellular signalling pathway(s). To address these issues, we have expressed and characterized recombinant mouse TRAIL. Specific detection with newly developed rabbit anti-TRAIL antibodies showed that the functional TRAIL molecule released into the supernatant of recombinant baculovirus-infected Sf9 cells is very similar to that associated with the membrane fraction of Sf9 cells. CD95L resistant myeloma cells were found to be sensitive to TRAIL, displaying apoptotic features similar to those of the CD95L- and TRAIL-sensitive T leukemia cells Jurkat. To assess if IL-1β-converting enzyme (ICE) and/or ICE-related proteases (IRPs) (caspases) are involved in TRAIL-induced apoptosis of both cell types, peptide inhibition experiments were performed. The irreversible IRP/caspase-inhibitor AcYVAD-cmk and the reversible IRP/caspase-inhibitor Ac-DEVD-CHO blocked the morphological changes, disorganization of plasma membrane phospholipids, DNA fragmentation, and loss of cell viability associated with TRAIL-induced apoptosis. In addition, cells undergoing TRAIL-mediated apoptosis displayed cleavage of poly(ADP)-ribose polymerase (PARP) that was completely blocked by Ac-DEVD-CHO.
These results indicate that TRAIL seems to complement the activity of the CD95 system as it allows cells, otherwise resistant, to undergo apoptosis triggered by specific extracellular ligands. Conversely, however, induction of apoptosis in sensitive cells by TRAIL involves IRPs/caspases in a fashion similar to CD95L. Thus, differential sensitivity to CD95L and TRAIL seems to map to the proximal signaling events associated with receptor triggering.
相似文献69.
Narendra Tuteja Ning Wu Huang Doris Skopac Renu Tuteja Sara Hrvatic Jianwen Zhang Sandor Pongor Grard Joseph Christian Faucher Franois Amalric Arturo Falaschi 《Gene》1995,160(2):143-148
The cDNA encoding human DNA helicase IV (HDH IV), a 100-kDa protein which unwinds DNA in the 5′ to 3′ direction with respect to the bound strand, was cloned and sequenced. It was found to be identical to the human cDNA encoding nucleolin, a ubiquitous eukaryotic protein essential for pre-ribosome assembly. HDH IV/nucleolin can unwind RNA-RNA duplexes, as well as DNA-DNA and DNA-RNA duplexes. Phosphorylation of HDH IV/nucleolin by cdc2 kinase and casein kinase II enhanced its unwinding activity in an additive way. The Gly-rich C-terminal domain possesses a limited ATP-dependent duplex-unwinding activity which contributes to the helicase activity of HDH IV/nucleolin. 相似文献
70.
Sara S. Tynan Niels H. Andersen Max T. Wills Laurence A. Harker Stephen R. Hanson 《Prostaglandins & other lipid mediators》1984,27(5):683-696
The ω-chain variant analogs of prostacyclin (PGI2) and PGD2 in which the n-amyl side-chain has been replaced by a cyclohexyl group have been prepared and their cardiovascular activities have been compared to those of BW-245C(Fig. 1)(1) a potent anti-aggregatory vasodilator bearing a cyclohexyl-terminated side-chain on a hydantoin skeleton. The cyclohexyl group has little effect on PGI2, but converts PGD2 to a long lasting hypotensive agent and increases the platelet anti-aggregatory potency of PGD2 by a factor of 8. The prostaglandin antagonist N-0164 selectively blocks the anti-aggregatory actions of PGD2, cyclohexyl-PGD2, and BW-245C; with essentially no effect on PGI2, cyclohexyl-PGI2 and PGE2 at comparably effective doses. The latter observation is contrary to an earlier report by MacIntyre (2,3), but supports the view that the anti-aggregatory effect of high doses of PGE2 () is mediated by the PGI2 receptor (4). The hydantoin acts at the platelet PGD2 receptor. 相似文献