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931.
Dr. Bruce W. Fouke Dr. C. J. Beets Dr. William J. Meyers Dr. Gilbert N. Hanson Dr. Allan J. Melillo 《Facies》1996,35(1):293-320
Summary The Seroe Domi Formation is a 350 m-thick sequence of Neogene marine limestones and silicilastic sandstones cropping out on
the leeward coast of Cura?ao, Netherlands Antilles. Integrated analyses of lithofacies, biostratigraphy, geochemistry and
Sr isotope model age analyses indicate that Seroe Domi Formation has experienced three major episodes of limestone diagenesis
and dolomitization (Dolomites I, I′, and II) that have taken place after successive Mio-Plio-Pleistocene depositional and
subaerial exposure events (Subunits 1, 2, and 3).
Subunit 1, the lowermost 30 to 100 m of the Seroe Domi Formation, is composed of interbedded coralgal grainstone gravity flows,
pelagic wackestones, and allochthonous blocks deposited in Middle Miocene deep-water (>500 m) fore-reef and carbonate slope
environments. Subunit 2, the uppermost 250 m of the Seroe Domi Formation, consists of coralgal packstones with basement-derived
siliciclastic sands that were deposted in shallowing fore-reef to reef-front environments during the Late Miocene to Pliocene.
Subunit 3 siliciclastic sandstones were deposited during the Early Pleistocene within erosional cavities in the Subunit 2
limestones, and are overlain by Late Pleistocene Quaternary Limestone Terraces.
The petrography, distribution and geochemistry of Dolomites I, I′ and II indicate that they were precipitated from seawater-freshwater
mixing zone fluid environments. Dolomite rhombs and meteoric calcite cements within biomolds illustrate that the host Seroe
Domi Formation limestones were subaerially exposed prior to each dolomitization event. Dolomite I (δ18O = +1.04 to +2.46% PDB; δ13C = −2.55 to −6.79 PDB;87Sr/86Sr=0.708866 to 0.708915; Zn=0 ppm; Cu=0 ppm) was precipitated from mixtures of seawater with isotopically-depleted freshwater
during the late Middle Miocene. Dolomite I′ (δ18O = +2.08 to +3.55 PDB, δ13C = −1.53 to 1.69 PDB,87Sr/86Sr=0.708981−0.709030; Zn=0 ppm; Cu=0 ppm) was also precipitated from mixtures of seawater with isotopically-depleted freshwater,
but during late Late Miocene. In contrast, Dolomite II (δ18O = +2.69 to +3.51 PDB; δ13C = −0.34 to +1.53 PDB;87Sr/86Sr=0.708954 to 0.709088; Zn=20 ppm; Cu=20 ppm) precipitated from late Early Pliocene mixtures of seawater with isotopically-depleted
freshwater that had derived Zn, Cu, and less-radiogenic Sr from basalts comprising the Cura?ao basement. 相似文献
932.
The bone resorbing agent, prostaglandin E2 (PGE2), was found to alter several components of the plasminogen activator (PA)/plasmin pathway in primary cultures of rat neonatal osteoblast-like cells. The mRNA and activities of both urokinase-type PA (uPA) and tissue-type PA (tPA) were enhanced by PGE2 treatment. The presence of mRNA for the uPA receptor (uPAR) has been demonstrated in these cells and steady-state levels shown to be greatly enhanced, the response being rapid and sustained for at least 24 hours. mRNA for plasminogen activator inhibitor 1 (PAI-1) was modulated in a biphasic manner, with inhibition of the constitutive level apparent at 4 hours of treatment and stimulation apparent at 12 hours and longer, while PAI-1 protein, measured by an ELISA assay for rat PAI-1, was diminished over this period. Neither PAI-2 mRNA nor mRNA for the broad spectrum protease inhibitor, protease nexin-1 (PN-1), was found to be modulated by PGE2. Therefore, PGE2 is likely to stimulate cell surface proteolytic activity, since uPA mRNA and cell-associated activity were elevated, as was mRNA for the cellular receptor for uPA. Although it was not possible to measure uPAR number and affinity it seems likely that elevated uPAR mRNA would translate into increased uPARs which would localize the increased uPA activity to the pericellular region. tPA mRNA and activity were also increased transiently with the activity inhibited with prolonged incubations, apparently by PAI-1. Elevation of tPA mRNA and activity may result in elevated activity within the extracellular matrix as tPA has been reported to associate with several matrix proteins. Thus the early effect of PGE2 would be to promote proteolysis, both pericellularly and in the extracellular matrix. The inhibition of PAI-1 mRNA and protein, which would contribute to the elevation of activity, is due to PGE2, but the later stimulatory effect on PAI-1 mRNA may be due to feedback regulation by transforming growth factor beta (TGFβ), secreted by osteoblasts and activated by elevated levels of PA. © 1995 Wiley-Liss Inc. 相似文献
933.
Andrew R. Klemer Len L. Hendzel David L. Findlay Randy A. Hedin Michael T. Mageau Allan Konopka 《Journal of phycology》1995,31(5):735-744
We hypothesize that the pattern of cyanobacterial dominance in experimentally enriched, low-carbon lakes is related not only to the resultant N:P ratio but also to the availability of carbon for gas-vesicle synthesis. We tested this hypothesis by determining the buoyancy responses of a highly gas-vacuolate, N2-fixing cyanobacterium to P enrichment with and without induced C limitation. Enrichment of samples of Aphanizomenon schindleri (Kling et al. 1994) from blooms in Lake 227 with combinations of C, N, and P produced rapid buoyancy reductions in P treatments, reductions that were reversed within a generation time in treatments that included C or C and N as well as P. These responses are the first of their kind to be observed in experiments with lake populations of cyano-bacteria. The rapid buoyancy reductions were associated with polyphosphate accumulations in P-treated A. schindleri. Differences in buoyancy status after one generation time were linked to differences in relative gas vacuolation between samples treated with P only and samples treated with C and N as well as P. These results may explain the relative success of different types of cyanobacteria in newly enriched, low-carbon lakes. The availability of C for gasvesicle synthesis may determine whether a low N:P ratio induces N2 fixation by benthic or by planktonic cyanobacteria and whether a high NP ratio leads to dominance by non-gas-vacuolate or by highly gas-vacuolate, non-N2-fixers. 相似文献
934.
Tania De Simone Ron S. Dickson Brian W. Skelton Allan H. White 《Inorganica chimica acta》1995,240(1-2):323-333
The phosphinoalkenes Ph2P(CH2)nCH=CH2 (n= 1, 2, 3) and phosphinoalkynes Ph2P(CH2)n C≡CR (R = H, N = 2, 3; R = CH3, N = 1) have been prepared and reacted with the dirhodium complex (η−C5H5)2Rh2(μ−CO) (μ−η2−CF3C2CF3). Six new complexes of the type (ν−C5H5)2(Rh2(CO) (μ−η1:η1−CF3C2CF3)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH3C5H4)Mn(CO)2thf resulted in coordination of the manganese to the alkene function. The Rh2---Mn complex [(η−C5H5)2Rh2(CO) (μ−η1:η1−CF3C2CF3) {Ph2P(CH2)3CH=CH2} (η−CH3C5H4)Mn(CO)2] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co2(CO)8 resulted in the coordination of Co2(CO)6 to the alkyne function. The Rh2---Co2 complex [(η−C5H5)2Rh2(CO) (μ−η1:η1−CF3C2CF3) {Ph2PCH2C≡CCH3}Co2(CO)2], C37H25Co2F6O7PRh2, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group
(Ci1, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on |F| was 0.052 fo observed (I > 3σ(I)) reflections. The Rh2 and Co2 parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh2 and perpendicular for Co2. Attempts to induce Rh2Co2 cluster formation were unsuccessful. 相似文献
935.
A number of in situ hybridization protocols using digoxigenin or biotin labelled probes were assessed for viral nucleic acid detection in formalin fixed, paraffin embedded tissue. Single-step detection protocols for biotin labelled probes produced low sensitivity; however, enzyme based one-step detection protocols for digoxigenin probes produced high sensitivity for both RNA and DNA systems. For both probe types, multistep detection protocols produced equally high sensitivity. Use of an enhanced APAAP procedure for digoxigenin labelled probes acheived maximal sensitivity without use of biotin-streptavidin reactions. The sensitivity of nucleic acid detection obtained with a digoxigenin labelled probe is comparable to that obtained using biotin. Digoxigenin labelled probes for nucleic acid detection are recommended for tissues with endogenous biotin. 相似文献
936.
§ D. Allan Butterfield Kenneth Hensley Pamela Cole Ramachandran Subramaniam †Michael Aksenov †Marina Aksenova ‡Paul M. Bummer ‡Boyd E. Haley †§John M. Carney 《Journal of neurochemistry》1997,68(6):2451-2457
Abstract: The activity of the astrocytic enzyme glutamine synthetase (GS) is decreased in the Alzheimer's disease brain, which may have relevance to mechanisms of chronic excitotoxicity. The molecular perturbation(s) that results in GS inactivation is not known, although oxidative lesioning of the enzyme is one likely cause. To assess structural perturbation induced in GS by metal-catalyzed oxidation, a series of spin-labeling studies were undertaken. Ovine GS was oxidized by exposure to iron/hydrogen peroxide and subsequently labeled with the thiol-specific nitroxide probe MTS [(1-oxyl-2,2,5,5-tetramethyl-pyrroline-3-methyl)methanethiosulfonate]. The reaction of MTS with cysteine residues within GS was monitored in real time by electron paramagnetic resonance spectrometry. Structural perturbation of GS, manifested as decreased thiol accessibility, was inferred from an apparent decrease in the rate constant for the second-order reaction of MTS with protein thiols. A subsequent spin-labeling study was undertaken to compare the structural integrity of GS purified and isolated from Alzheimer's disease-afflicted brain (AD-GS) with that of GS isolated from nondemented, age-matched control brain (C-GS). The rate constant for reaction of MTS with AD-GS was markedly decreased relative to that for the reaction of spin label with C-GS. The kinetic data were partially corroborated by spectroscopic data obtained from circular dichroism analysis of control and peroxide-treated ovine GS. In an adjunct experiment, the interaction of GS with a synthetic analogue of the Alzheimer's-associated β-amyloid peptide, known to induce free radical oxidative stress, indicated strong interaction of the enzyme with the peptide as reflected by a decrease in the rate constant for MTS binding to reactive protein thiols. 相似文献
937.
938.
A connection between pre-mRNA splicing and the cell cycle in fission yeast: cdc28+ is allelic with prp8+ and encodes an RNA-dependent ATPase/helicase. 总被引:5,自引:0,他引:5
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K Lundgren S Allan S Urushiyama T Tani Y Ohshima D Frendewey D Beach 《Molecular biology of the cell》1996,7(7):1083-1094
The fission-yeast gene cdc28+ was originally identified in a screen for temperature-sensitive mutants that exhibit a cell-division cycle arrest and was found to be required for mitosis. We undertook a study of this gene to understand more fully the general requirements for entry into mitosis. Cells carrying the conditional lethal cdc28-P8 mutation divide once and arrest in G2 after being shifted to the restrictive temperature. We cloned the cdc28+ gene by complementation of the temperature-sensitive growth arrest in cdc28-P8. DNA sequence analysis indicated that cdc28+ encodes a member of the DEAH-box family of putative RNA-dependent ATPases or helicases. The Cdc28 protein is most similar to the Prp2, Prp16, and Prp22 proteins from budding yeast, which are required for the splicing of mRNA precursors. Consistent with this similarity, the cdc28-P8 mutant accumulates unspliced precursors at the restrictive temperature. Independently, we isolated a temperature-sensitive pre-mRNA splicing mutant prp8-1 that exhibits a cell-cycle phenotype identical to that of cdc28-P8. We have shown that cdc28 and prp8 are allelic. These results suggest a connection between pre-mRNA splicing and progression through the cell cycle. 相似文献
939.
Antagonism against the grey mould pathogen Botrytis cinerea by Pseudomonas antimicrobica was demonstrated in vitro and in vivo. Cell-free filtrates showed activity against B. cinerea growing on Potato Dextrose Agar (PDA) in a media-dependent manner with the most distinct antagonism being produced in Czapek Dox Broth (CDB). Cell-free filtrates of CDB-grown cultures also significantly reduced conidial germination of B. cinerea. An assays based on the inhibition of conidial germination was compared with two assays measuring the antagonism of mycelial growth on PDA. The conidial germination bioassay was more sensitive in the detection of this antifungal activity than the Petri dish bioassay while a bioassay using Microdetection plates did not detect antagonism due to the small loading capacity of the latter. The conidial germination bioassay was modified for detection of antibiosis on the surface of strawberry leaves. Significant reductions in percentage conidial germination were recorded on the surface of leaves of both micropropagated and glasshouse grown strawberry plants when the antifungal compounds of Ps. antimicrobica were applied to the leaf tissue with the conidia. In addition, antifungal compounds were also detectable when conidia were applied to leaf tissue which had previously been sprayed with cells of Ps. antimicrobica. These tests indicate that Ps. antimicrobica would be a suitable biocontrol agent for the control of B. cinerea. 相似文献
940.
Robin D Allan Helena W Dickenson Graham A.R Johnston Rymantas Kazlauskas Kenneth N Mewett 《Neurochemistry international》1997,30(6):197-591
Structural analogues of ZAPA, Z-3-[(aminoiminomethyl)thio]prop-2-enoic acid, an isothiouronium analogue of GABA, are potent GABAA agonists as seen in the isolated guinea-pig ileum and in the facilitation of [3H]diazepam binding to rat brain membranes. Compounds with guanidino or amidine groups replacing the amino functionality of GABA were also found to be active. The highest activity was displayed by the isothiouronium salts in which the conformational flexibility of the molecule is restricted by a Z-substituted carbon–carbon double bond. A series of bis-isothiouronium compounds was prepared from aliphatic ,ω-bis-thioureas as mixtures of E and Z adducts. Maximum GABAA agonist activity for this series was found with a C6–C8 carbon chain, and the results were consistent with an interaction at the GABAA receptor with only one end of the molecule, rather than the more potent effect expected of a molecule bridging two active sites. GABAA antagonist/partial agonist activity was observed on the guinea-pig isolated ileum for a number of different analogue types, with the most potent being bis-isothiouronium derivatives. None of the substituted derivatives of ZAPA was as active as ZAPA itself, and maximum GABAA activity was found in the n-pentyl and n-hexyl analogues. 相似文献