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The seasonal growth and decline of a population of Elodea canadensis Mich. growing in an irrigation drain are described, together with some characteristics of the aquatic environment (turbidity, photosynthetically-available radiation, temperature and pH). Overwintering buds (up to 5000 m?2) in the form of swollen dormant stem apices are produced in autumn with the onset of cold weather, remain in the mud, and grow out in the spring. In late summer vegetative reproduction also occurs when large numbers of the leafless stem portions which are capable of growing into independent plants are swept downstream from established populations. Results suggest that control measures should be applied in early summer when populations are approaching nuisance size, and again in late summer before fragmentation occurs and overwintering propagules are initiated. In irrigation channels in Australia, where draining and drying are not feasible, biomass in successfully reduced by widespread use of herbicides. 相似文献
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Kathleen Postle 《Journal of bioenergetics and biomembranes》1993,25(6):591-601
TonB protein couples cytoplasmic membrane electrochemical potential to active transport of iron-siderophore complexes and vitamin B12 through high-affinity outer membrane receptors of Gram-negative bacteria. The mechanism of energy transduction remains to be determined, but important concepts have already begun to emerge. Consistent with its function, TonB is anchored in the cytoplasmic membrane by its uncleaved amino terminus while largely occupying the periplasm. Both the connection to the cytoplasmic membrane and the amino acid sequences of the anchor are essential for activity. TonB directly associates with a number of envelope proteins, among them the outer membrane receptors and cytoplasmic membrane protein ExbB. ExbB and TonB interact through their respective transmembrane domains. ExbB is proposed to recycle TonB to an active conformation following energy transduction to the outer membrane. TonB most likely associates with the outer membrane receptors through its carboxy terminus, which is required for function. In contrast, the novel prolinerich region of TonB can be deleted without affecting function. A model that incorporates this information, as well as tempered speculation, is presented. 相似文献
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Affinity Purification of Synenkephalin-Containing Peptides Including a Novel 23.3-Kilodalton Species 总被引:1,自引:1,他引:0
Abstract: Affinity chromatography has been used for rapid and high-yield purification of synenkephalin (proenkephalin 1 -70) containing peptides present in bovine adrenal medulla (BAM) chromaffin granular lysate. A column of CN-Br-activated Sepharose 4B coupled to synenkephalin antiserum bound synenkephalin immunoreactivity which was eluted by a stepwise gradient of 50 mM ammonium acetate containing 20% (vol/vol) acetonitrile over the pH range 7–3. Synenkephalin immunoreactivity emerged as two peaks, eluting at pH 5.5 and 4.5. Characterization of the two peaks by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting indicated that the pH 5.5 peak contained principally low-molecular-weight proenkephalin species (8.6 and 12.6 kilodaltons), whereas the pH 4.5 peak contained, in addition, high-molecular-weight proenkephalin species (18.2 and 23.3 kilodaltons). The 8.6- and 12.6- kilodalton species were isolated from the pH 5.5 peak by TSK gel filtration HPLC, whereas the pH 4.5 peak was further purified by passage over successive affinity columns coupled to antiserum against BAM 22P (proenkephalin 182–203) and [Met5 ]-enkephalin-Arg6 -Gly7 -Leu8 . The former column retains the 23.3-kilodalton species, whereas the latter column retains the 18.2-kilodalton species. The 23.3- kilodalton peptide represents a novel putative proenkephalin intermediate (proenkephalin-1–206), containing [Leu5 ]- enkephalin at the C-terminus. 相似文献
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Begonia (sect.Gireoudia)lyman-smithii is described and illustrated, and its relationships are discussed. 相似文献
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Studies of Río Negro subsistence farming and fishing activities are used to estimate the human carrying capacity for the region and the likely pattern of human land-use during prehistory. Ceramic evidence suggests human presence in the region more than 3000 years ago. Traditional farming is labor intensive and relatively unproductive. Nevertheless, farmers achieve an energy return of 15.21, and produce 2600 kcal per work hour. Fish are the major protein source, but fish catch per unit of effort and fish yield per hectare of floodplain are very low; fishermen are probably exploiting local fish resources very close to their limit. The low human population density would suggest that the Río Negro forest has been relatively undisturbed. Nevertheless, charcoal is widespread and abundant in forest soils. This charcoal is probably from anthropogenic or natural wildfires. These results suggest a much more complex history for Amazonia than previously thought.K. Clark is a free-lance biologist residing in Lima, Peru 相似文献
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The glue protein of ribbed mussels (Geukensia demissa): a natural adhesive with some features of collagen 总被引:1,自引:0,他引:1
J. Herbert Waite Douglas C. Hansen Kathleen T. Little 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1989,159(5):517-525
Summary The Atlantic ribbed musselGeukensia (Modiolus)demissa attaches itself to the roots of cord grass and other hard objects in tidal salt marshes by spinning adhesive byssal threads. The precursor of a protein apparently present in the adhesive plaques of the threads was isolated in quantity from the foot of the mussel. The protein has an apparent molecular weight of 130000, a pI of 8.1, and contains a high proportion of Gly, Glu/Gln, Lys and 3,4-dihydroxyphenyl-l-alanine (DOPA). Sequence of tryptic peptides suggests a pattern of repeated motifs, such as: Gly-DOPA-Lys, and X-Gly-DOPA-Y-Z-Gly-DOPA/Tyr-Lys, where X is Thr or Ala in octapeptides and Gln-Thr in nonapeptides. Y is variable, but more often than not hydrophobic; and Z is frequently Pro or 4-trans-hydroxyproline (Hyp). The presence of Pro-Gly and Hyp-Gly sequences of -hydroxylysine in the protein is reminiscent of typical collagens; however, the protein is not labile to clostridial collagenase, nor does collagen cross-react with antibodies raised against the mussel protein. Unlike typical collagens, Gly probably occurs only at every 4th or 5th residue in this unusual mussel protein.Abbreviations
Anti-Gdfp
anti-G. demissa foot protein
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Dopa
3,4-dihydroxyphenylalanine
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CTAB
cetyltrimethylammonium bromide
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HPLC
high performance liquid chromatography
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PAGE
polyacrylamide gel electrophoresis
Supported by grants from the National Science Foundation (DMB 8500301) and the Office of Naval Research (N00014-86K-0717) 相似文献
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The bioactivity of growth hormone releasing hormone 1-29 [GHRH(1-29)NH2] has been compared with that of an agonist analogue [Ac-D-Tyr1,D-Ala2]-GHRH(1-29)NH2, in normal male volunteers. Using a submaximal dose of 3 micrograms/kg administered subcutaneously, peak growth hormone (GH) response and area under the GH curve were similar for the native and agonist analogue. In addition, no significant differences were found in peak GHRH(1-29) immunoreactivity, area under the GHRH(1-29) curves or plasma disappearance rates of the two peptides. The results suggest that, in keeping with the relative activities of other "superactive" analogues tested so far, the greatly enhanced activity of [Ac-D-Tyr1,D-Ala2]-GHRH(1-29)NH2 observed in the rat is not found in humans. It is possible that this species difference is due to differences in the interaction of GHRH peptides with the rat and the human somatotroph GHRH receptor. 相似文献