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21.
Robert E. Lemon Charles W. Dobson Peter G. Clifton 《Ethology : formerly Zeitschrift fur Tierpsychologie》1993,93(3):198-210
In order to determine the rules of sequencing of songs used by American redstarts, we related Markovian and hierarchical models to recordings obtained from free-living males. In the smaller repertoires of three or four songs, low order Markov chain models fitted the data. 9 of the 10 sequences so examined were first-order, and the last was second-order. Larger repertoires of 6 and 8 songs were hierarchical in organization with subsets of songs having independent sequencing rules. Most samples of singing were stationary in their transition rules over periods of several days: non-stationarity was sometimes associated with a change in the number of songs forming the sequence, or in repetitions of songs. We examine causal models of song sequencing and conclude that our results generally favor competition models, although some sequential dependencies may also apply. Hierarchical organization in the serial repertoires of American redstarts may reflect developmental influences rather than effects of repertoire size itself. 相似文献
22.
Samples of suspended particulate matter (SPM) collected from the Humber Estuary had higher concentrations of particulate metals
than SPM from Holderness coastal waters (U.K.). Characterised SPM from both sources was used in laboratory experiments involving
the uptake of radiotracer109Cd,137Cs,54Mn and65Zn. Kinetic experiments, over five days, showed that the rate and extent of uptake was highly dependent on particle type,
with109Cd,54Mn and65Zn being more reactive with Humber Estuary particles than those from Holderness and137Cs having the opposite trend. Adsorption experiments were also carried out on suspensions in which SPM from the Humber Estuary
and Holderness coastal water were mixed in various proportions. These experiments revealed that Kd for65Zn increased linearly with the proportion of Humber SPM, Kd for137Cs decreased linearly with increase in Humber SPM and Kd for54Mn and109Cd displayed non-linear behaviour. The results of the study were used to develop an algorithm for predicting the partition
coefficients in the Humber Plume based on the extent of particle mixing from the two source regions. The use of206/207Pb ratios in determining the extent of particle mixing is discussed, along with the application of the algorithm to the modelling
of particulate trace metal behaviour in the Humber-Wash coastal zone. 相似文献
23.
Summary Changes in the plasma membrane surface and in the cortical cytoplasm during wound healing in giant green algal cells ofErnodesmis verticillata (Kützing) Brgesen were followed using scanning and transmission electron microscopy. Microvillus-like structures that contain cytoplasmic and cytoskeletal constituents were observed emanating from the surface of the plasma membrane at the retracting/cut end of wounded cells. These delicate structures seem to be remnants of cell wall-plasmalemma connections that draw out the plasma membrane and cortical components from the contracting cytoplasm as it pulls away from the cell wall. Most of these connections break during wound healing and, when contraction stops, the microvillus-like protrusions become progressively shorter. In cells treated with a calmodulin antagonist (W-7), a number of distinctive bodies accumulate that are of unknown composition, are oblong in shape, and have a diameter slightly smaller than the protoplasmic protrusions. Ultrastructural and other data indicate that these bodies result from retrieved constituents of the plasma-membrane protrusions, as they do not accumulate in unwounded drugtreated cells or in cells treated in W-5. These findings suggest that the protoplasmic protrusions accumulate membrane and cytoplasmic components that are retrieved and recycled during wound healing inErnodesmis by a novel mechanism. The combined plasma membrane surfaces of the microvillus-like protrusions may help to account for the drastic decrease in surface area that occurs during wound healing.Abbreviations SEM
scanning electron microscopy
- TEM
transmission electron microscopy
- W-7
N-[6-aminohexyl]-5-chloro-1-naph-thalenesulfonamide
- W-5
N-[6-aminohexyl]-1-naphthalenesulfonamide 相似文献
24.
Summary The perdeuteration of aliphatic sites in large proteins has been shown to greatly facilitate the process of sequential backbone and side-chain 13C assignments and has also been utilized in obtaining long-range NOE distance restraints for structure calculations. To obtain the maximum information from a 4D 15N/15N-separated NOESY, as many main-chain and side-chain 1HN/15N resonances as possible must be assigned. Traditionally, only backbone amide 1HN/15N resonances are assigned by correlation experiments, whereas slowly exchanging side-chain amide, amino, and guanidino protons are assigned by NOEs to side-chain aliphatic protons. In a perdeuterated protein, however, there is a minimal number of such protons. We have therefore developed several gradient-enhanced and sensitivity-enhanced pulse sequences, containing water-flipback pulses, to provide through-bond correlations of the aliphatic side-chain 1HN/15N resonances to side-chain 13C resonances with high sensitivity: NH2-filtered 2D 1H-15N HSQC (H2N-HSQC), 3D H2N(CO)C/ and 3D H2N(COC/)C/ for glutamine and asparagine side-chain amide groups; 2D refocused H(N/)C/ and H(N/C/)C/ for arginine side-chain amino groups and non-refocused versions for lysine side-chain amino groups; and 2D refocused H(N)C and nonrefocused H(N.)C for arginine side-chain guanidino groups. These pulse sequences have been applied to perdeuterated 13C-/15N-labeled human carbonic anhydrase II (2H-HCA II). Because more than 95% of all side-chain 13C resonances in 2H-HCA II have already been assigned with the C(CC)(CO)NH experiment, the assignment of the side-chain 1HN/15N resonances has been straightforward using the pulse sequences mentioned above. The importance of assigning these side-chain HN protons has been demonstrated by recent studies in which the calculation of protein global folds was simulated using only 1HN-1HN NOE restraints. In these studies, the inclusion of NOE restraints to side-chain HN protons significantly improved the quality of the global fold that could be determined for a perdeuterated protein [R.A. Venters et al. (1995) J. Am. Chem. Soc., 117, 9592–9593].To whom correspondence should be addressed. 相似文献
25.
26.
Reactions of Cr(CO)3(η6-BT), in which the Cr is π-coordinated to the benzene ring of benzo[b]thiophene (BT), with Cp′(CO)2Re(THF), where Cp′ = η5-C5H5 or η5-C5Me5, give the products Cp′(CO)2Re(η2:η6-μ2-BT)Cr(CO)3 in which the Cr remains coordinated to the benzene ring and Re is bound to the C(2)=C(3) double bond. An X-ray diffraction study of Cp(CO)2Re(η2:η6-μ2-BT)Cr(CO)3 (3) provides details of the geometry. This structure contrasts with that of the Cp′(CO)2Re(BT) complexes that exist as mixtures of isomers in which the BT is coordinated to the Re through either the double bond (2,3-η2) or the sulfur (η1(S)). Thus, the electron-withdrawing Cr(CO)3 group in 3 stabilizes the 2,3-η2 mode of BT coordination to the Cp′(CO)2Re fragment. Implications of these results for catalytic hydrodesulfurization of BT are discussed. Crystal data for 3: triclinic, space group . 相似文献
27.
Body water content was determined on groups of Cyprinodon variegatus after sequential acclimation to ambient salinities in the range from fresh water to 100%. A multiple linear regression model applied to the data included body mass ( M ) of individuals and acclimation salinity ( S ) as independent variables, and body water content ( W ) as the dependent variable. The model that described the relationship was W (g) = 0·059 + 0·723 M (g)–0001 S (%). Converting values of body water content to percent of wet body mass produced a range of values from 74·5% in fresh water to 72·0% at 100%, only a 2·5% difference in body water content over this wide range of ambient salinities. 相似文献
28.
Virginia L. Smith-Swintosky †Stephen Zimmer ‡John W. Fenton II Mark P. Mattson 《Journal of neurochemistry》1995,65(3):1415-1418
Abstract: Amyloid β-peptide (Aβ) is the principal component of neuritic plaques in the brain in Alzheimer's disease (AD). Recent studies revealed that Aβ can be neurotoxic by a mechanism involving free radical production and loss of cellular ion homeostasis, thus implicating Aβ as a key factor in the pathogenesis of AD. However, other proteins are present in plaques in AD, including the protease thrombin and protease nexin-1 (PN1), a thrombin inhibitor. We therefore tested the hypothesis that thrombin and PN1 modify neuronal vulnerability to Aβ toxicity. In dissociated rat hippocampal cell cultures the toxicity of Aβ was significantly enhanced by coincubation with thrombin, whereas PN1 protected neurons against Aβ toxicity. Aβ induced an increase in levels of intracellular peroxides and calcium. Thrombin enhanced, and PN1 attenuated, the accumulation of peroxides and calcium induced by Aβ. Taken together, these data demonstrate that thrombin and PN1 have opposing effects on neuronal vulnerability to Aβ and suggest that thrombin and PN1 play roles in the pathogenesis of neuronal injury in AD. 相似文献
29.
Tadashi II Masayuki Kubota Takashi Hirano Mamoru Ohashi Keiichi Yoshida Sakaru Suzuki 《Glycoconjugate journal》1995,12(3):282-289
The fast atom bombardment (FAB) collision induced dissociation (CID)-mass spectrometry/mass spectrometry (MS/MS) technique was successfully applied to characterize and identify the structures of the immunoreactive trisulfated and tetrasulfated tetrasaccharides that were obtained from the chondroitin sulfate in a shark fin using a treatment with chondroitinase ABC.Abbreviations FABMS
fast atom bombardment mass spectrometry
- CID
collision induced dissociation
- MS/MS
mass spectrometry/mass spectrometry
- UA2S-GalNAc6S
2-acetamido-2-deoxy-3-O-(2-O-sulfo--d-gluco-4-enepyranosyluronic acid)-6-O-sulfo-d-galactose
- UA-GalNAc4S
2-acetamido-2-deoxy-3-O-(-d-gluco-4-enepyranosyluronic acid)-4-O-sulfo-d-galactose
- UA-GalNAcDiS
2-acetamido-2-deoxy-3-O-(-d-gluco-4-enepyranosyluronic acid)-4,6-di-O-sulfo-d-galactose 相似文献
30.
Ecomorphological correlates in ten species of subtropical seagrass fishes: diet and microhabitat utilization 总被引:6,自引:0,他引:6
Philip J. Motta Kari B. Clifton Patricia Hernandez Bradley T. Eggold 《Environmental Biology of Fishes》1995,44(1-3):37-60
Synopsis Ecomorphological correlates were sought among ten species of distantly related subtropical seagrass fishes. Morphometric data associated with feeding and microhabitat utilization were compared by principal components analysis, cluster analysis, and canonical correspondence analysis to dietary data. Morphology was generally a poor predictor of diet except for a group of mid-water planktotrophic filter feeders. Separation of the species along morphological axes appears to be related more to microhabitat utilization resulting in three major groups: (1) a group of planktotrophic, mid-water fishes specialized for cruising and seeking out evasive prey characterized by a compressed fusiform body, forked caudal fin, long, closely spaced gill rakers, short to intermediate! length pectoral fin, pointed pectoral fin, large lateral eye, short head, and a terminal or subterminal mouth; (2) slow swimming, less maneuverable epibenthic fishes that pick or suck their prey off the substrate. They are united by more rounded caudal and pectoral fins, and short or no gill rakers; and (3) a group of more mobile and maneuverable epibenthic foragers characterized by a more compressed, sub-gibbose body, long, pointed pectoral fins, forked caudal fins, large lateral eyes, subterminal mouth, and greater jaw protrusibility. Cases of convergence in trophic and microhabitat utilization characters were apparent in some of the groups. 相似文献