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111.
Else Marie Friis Kaj Raunsgaard Pedersen Peter R. Crane 《American journal of botany》1995,82(7):933-943
A new genus and species of fossil angiosperm (Appomattoxia ancistrophora) is established based on well-preserved fruiting units and associated pollen from the Early Cretaceous (Early or Middle Albian) Puddledock locality in the Potomac Group sequence of Virginia, eastern North America. Fruiting units are small, unilocular, and with a single, pendulous, orthotropous seed. The fruit surface is characterized by densely spaced unicellular spines with hooklike tips, which probably functioned in biotic dispersal. Pollen grains adhering to the stigmatic area of many specimens are monocolpate and tectate with granular to columellate infratectal structure, and are similar to dispersed grains assigned to Tucanopollis and Transitoripollis. Comparison of fossil Appomattoxia ancistrophora with extant plants reveals an unusual combination of characters that includes similarities with some magnoliid taxa, particularly Piperales (Piperaceae, Saururaceae) and Laurales (Chloranthaceae), as well as the monotypic ranunculid family Circaeasteraceae. Appomattoxia ancistrophora differs from extant Piperales in having a pendulous rather than erect ovule, and differs from extant Circaeaster in details of the fruit wall, as well as the presence of monosulcate rather than tricolpate pollen. 相似文献
112.
Site selective bis-intercalation of a homodimeric thiazole orange dye in DNA oligonucleotides. 总被引:2,自引:1,他引:1
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We have used one and two dimensional 1H NMR spectroscopy to characterize the binding of a homodimeric thiazole orange dye, 1,1'-(4,4,8,8-tetramethyl-4,8-diaza-undecamethylene)-bis-4- (3-methyl-2,3-dihydro-(benzo-1,3-thiazole)-2-methylidene)-quinolin ium tetraiodide (TOTO), to various double stranded DNA oligonucleotides. TOTO binds strongly to all the oligonucleotides used, but usually more than one complex is observed and exchange between different binding sites broadens the lines in the NMR spectra. Complete precipitation occurs when TOTO is bound to small oligonucleotides. Binding to larger oligonucleotides occurs by bis-intercalation. The 1:1 complex of TOTO with the oligonucleotide d(CCGACTGATGC):d (GCATCAGTCGG) gave only one complex that was shown to be a bis-intercalation in the CTGA:TCAG binding site. The binding to this site was also characterized by studying the TOTO complex with the d(CCGCTGAGC):d(GCTCAGCGG) oligonucleotide. NOE connectivities and molecular modelling were used to characterize the complex. The 1:1 complex of TOTO with the oligonucleotide d(CCGCTAGCG):d(CGCTAGCGG) containing a CTAG:CTAG binding site was similarly characterized by NMR. It was concluded that the binding of TOTO to larger oligonucleotides is site selective with CTAG:CTAG as the preferred binding site. 相似文献
113.
Kenneth P. Severin JoLynn Carroll Brenda L. Norcross 《Environmental Biology of Fishes》1995,43(3):269-283
Synopsis The incorporation of dissolved oceanic constituents in the otoliths of fish has potential as a chemical tracer for reconstructing the early life history of marine fish. Wavelength dispersive spectrometers on an electron microprobe were used to measure Na, Mg, P, S, Cl, K, Ca, and Sr concentrations on the outer margins of 57 juvenile walleye pollock, Theragra chalcogramma, otoliths from five locations in the Gulf of Alaska and Bering Sea. Discriminant analyses that used various combinations of Na, P, K, Sr, and fish standard length and/or age showed that 60–80% of the samples could be assigned to the correct capture locality. While the concentrations of some of the measured elements correlated with standard length or age of the fish, there are measurable differences among localities when concentrations are length or age corrected, mainly due to differences in Na and K concentrations. Elemental composition of otoliths potentially could be used to assign fish from a mixed stock fishery to original stocks, information that is greatly needed for the effective management of fish stocks. 相似文献
114.
David W. Deerfield Douglas J. Fox Martin Head-Gordon Richard G. Hiskey Lee G. Pedersen 《Proteins》1995,21(3):244-255
The first coordination shell of an Mg(II) ion in a model protein environment is studied. Complexes containing a model carboxylate, an Mg(II) ion, various ligands (NH3, H2S, imidazole, and formaldehyde) and water of hydration about the divalent metal ion were geometry optimized. We find that for complexes with the same coordination number, the unidentate carboxylate–Mg(II) ion is greater than 10 kcal mol?1 more stable than the bidentate orientation. Imidazole was found to be the most stable ligand, followed in order by NH3 formaldehyde, H2O, and H2S. © 1995 Wiley-Liss, Inc. 相似文献
115.
Removal of toluene in waste gases using a biological trickling filter 总被引:12,自引:0,他引:12
The removal of toluene from waste gas was studied in a trickling biofilter. A high level of water recirculation (4.7 m h–1) was maintained in order to keep the liquid phase concentration constant and to achieve a high degree of wetting. For loads in the range from 6 to 150 g m–3 h–1 the maximum volumetric removal rate (elimination capacity) was 35±10 g m–3 h–1, corresponding to a zero order removal rate of 0.11±0.03 g m–2 h–1 per unit of nominal surface area. The surface removal was zero order above the liquid phase concentrations of approximately 1.0 g m–3, corresponding to inlet gas concentrations above 0.7–0.8 g m–3. Below this concentration the surface removal was roughly of first order. The magnitude of the first order surface removal rate constant, k1A
, was estimated to be 0.08–0.27 m h–1 (k1A
a=24–86 h–1). Near-equilibrium conditions existed in the gas effluent, so mass transfer from gas to liquid was obviously relatively fast compared to the biological degradation. An analytical model based on a constant liquid phase concentration through the trickling filter column predicts the effluent gas concentration and the liquid phase concentration for a first and a zero order surface removal. The experimental results were in reasonable agreement with a very simple model valid for conditions with an overall removal governed by the biological degradation and independent of the gas/liquid mass transfer. The overall liquid mass transfer coefficient, KLa, was found to be a factor 6 higher in the system with biofilm compared to the system without. The difference may be explained by: 1. Difference in the wetting of the packing material, 2. Mass transfer occurring directly from the gas phase to the biofilm, and 3. Enlarged contact area between the gas phase and the biofilm due to a rough biofilm surface. 相似文献
116.
Brenda J. Claiborne Allen I. Selverston 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1984,154(1):27-32
Summary The cell bodies of the inferior ventricular nerve (IVN) through-fibers of the lobster stomatogastric nervous system were located using cobalt chloride backfills and intracellular recordings. Following backfills of the IVN, two cell bodies in the supraesophageal ganglion (or brain) were stained with cobalt. These cells, each approximately 30 m in diameter, were located at the base of the IVN, just inside the connective tissue sheath surrounding the brain, and were identifiable on the basis of their close proximity to the IVN.In order to record from the cells, an in vitro preparation was made which included the cell bodies, their axons in the IVN and the stomatogastric nervous system. Intracellular recordings showed that the axons projected to the stomatogastric ganglion and made synaptic connections onto identified neurons. The axon trajectories and synaptic connections correlated with those previously described for the IVN through-fibers using extracellular stimulation and recording techniques.Abbreviations
IVN
inferior ventricular nerve
-
SN
stomatogastric nerve 相似文献
117.
Summary We examined metaphases from three patients with chronic myeloid leukaemia and a typical Philadelphia chromosome with one chromosome 9 as the recipient to determine whether the 9q+ 22q- translocation is reciprocal. Good quality G-banded photographs of the chromosomes concerned were subjected to light absorption density analysis. This provided enlarged tracings corresponding to the relevant chromosome regions and so facilitated accurate measurement. This technique has unambiguously shown that the typical Philadelphia chromosome results from a reciprocal translocation and that probably no material is gained or lost in the exchange. Furthermore, in a total of six patients for whom sequential G and C banding was performed, the chromosome 9 with the largest block of centromeric heterochromatin received the translocated material. We offer tentative explanations for this curious observation. 相似文献
118.
Exogenous nucleosides, either singly or in combination, do not enhance postimplantation development of mouse embryos in vitro, and adenosine, guanosine and thymidine are toxic to the embryos at high concentrations. 相似文献
119.
Polyol accumulation by two filamentous fungi grown at different concentrations of NaCl 总被引:1,自引:0,他引:1
The accumulation of polyols by Aspergillus niger (van Tiegh) strain S 1 and Penicillium chrysogenum (Thom) strain S 30 was followed during growth in media of different concentrations of NaCl. The major polyols found were glycerol, erythritol and mannitol. The total polyol pool increased in both organisms in response to raised salinity, and the proportion of glycerol and erythritol was markedly enhanced at high salinity. 相似文献
120.
Brenda Walker Griffin Charles Marth Yukio Yasukochi Bettie Sue Siler Masters 《Archives of biochemistry and biophysics》1980,205(2):543-553
Under identical experimental conditions, purified preparations of rabbit liver microsomal cytochrome P-450 and beef heart metmyoglobin were equally effective at stimulating the oxidation of aminopyrine to a free radical species by cumene hydroperoxide. Mannitol had no effect on radical levels produced with either hemeprotein-hydroperoxide system; however, specific ligands of the two hemeproteins, substrates of cytochrome P-450, and phospholipid affected the two systems quite differently. Only the metmyo-globindependent oxidation of aminopyrine was significantly inhibited by fluoride and cyanide. Metyrapone, a specific ligand of cytochrome P-450, and benzphetamine, which was N-demethylated by cumene hydroperoxide only in the presence of cytochrome P-450, inhibited only the cytochrome P-450-stimulated oxidation of aminopyrine. Moreover, only with the solubilized liver hemeprotein was aminopyrine radical generation markedly stimulated by phospholipid. Similar properties of aminopyrine N-demethylation and radical formation by the cytochrome P-450-cumene hydroperoxide system have strongly implicated the radical as a requisite intermediate in product formation. Micromolar concentrations of metyrapone caused parallel inhibition, by at least 50%, of both radical generation and formaldehyde production. These results support a radical pathway of N-demethylation proposed for other hemeprotein-hydroperoxide systems (B. W. Griffin and P. L. Ting, 1978, Biochemistry, 17, 2206–2211), in which the substrate undergoes two successive one-electron abstractions, followed by hydrolysis of the iminium cation intermediate. Thus, for this class of substrates, the experimental data are consistent with the oxygen atom of the product arising from H2O and not directly from the hydroperoxide, which has been previously proposed as a general mechanism for cytochrome P-450 peroxidatic activities. 相似文献