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The feeding habits of the filter-feeding fairy shrimp Streptocephalus proboscideus are documented experimentally by offering them ciliates, Volvox, rotifers, nematodes and small crustaceans as prey. Escape capabilities (e.g. swimming speed) rather than size or shape were found to determine these animals' vulnerability to predation by the fairy shrimp. Ingestion rates for Volvox increased hyperbolically with size and, at the high temperatures in which they live, fairy shrimps may daily remove the equivalent of their body weight from the environment. 相似文献
54.
Theoretical and experimental investigations on the conformations of synthetic polytripeptides, with Gly-R2-R3 general repetitive sequence, are of great interest for the comprehension of the factors wich contribute to the triple helix stabilization.Using appropriate molecules as models, we have investigated by the PCILO method the intrinsic conformational possibilities of each « in situresidue for the following cases: Gly-imino-imino, Gly-amino-imino and Gly-imino-amino which represent the most important sequences occuring in the primary structure of collagen. The computations were carried out taking into account the two pyrrolidine ring puckerings and the preferential side-chains orientations.Extending our previous work concerning the isomeric polytripeptides Gly-X-Pro and Gly-Pro-X with X {Pro, Phe} we have studied the cases of X {Ala, Ser}. In this brief communication, we present a preliminary synthesis of these recent results. 相似文献
55.
A gas chromatographic method has been satisfactorily developed for the determination of gallic acid after enzymatic hydrolysis of methyl gallate by fungal tannase. The technique described herein permits a specific, quantitative analysis of the enzyme. The separate determination of both soluble and fixed tannase is described. 相似文献
56.
Van Onckelen Henri A.; Horemans Stefaan; De Greef Jan A. 《Plant & cell physiology》1981,22(3):507-515
During the early stages of germination and vegetative development,cotyledons of intact bean (Phaseolus vulgaris L.) seedlingsshowed active ABA catabolism causing a low endogenous ABA content.At the end of the substrate mobilizing phase, when the cotyledonsbecame senescent, a drastic increase of the endogenous ABA contentlinked with a decrease of the ABA catabolic activity was observed.This indicates that a close connection exists between senescenceand endogenous ABA content and metabolism in bean cotyledons. Removal of the apical growth region induced in the cotyledonsactivation of the ABA catabolism and the endogenous ABA concentrationdecreased below the detection limit (0.1 ng/g fr wt) at theonset of the outgrowth of the axillary buds. From then, apicaldominance was restored and the cotyledons returned to the senescentstate, which was correlated with a drastic increase of theirendogenous ABA content.
1 Bevoegd verklaard navorser N. F. W. O.
2 Wetenschappelijk medewerker F. K. F. O. (Received November 25, 1980; Accepted February 13, 1981) 相似文献
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58.
Alice Y. Romans Theresa M. Allen William Meckes Robert Chiovetti Lulu Sheng Henri Kercret Jere P. Segrest 《生物化学与生物物理学报:生物膜》1981,642(1):135-148
Human erythrocyte glycophorin is one of the best characterized integral membrane proteins. Reconstitution of the membrane-spanning hydrophobic segment of glycophorin (the tryptic insoluble peptide released when glycophorin is treated with trypsin) with liposomes results in the production of freeze-fracture intrabilayer particles of 80 Å diameter (Segrest, J.P., Gulik-Krzywicki, T. and Sardet, C. (1974) Proc. Natl. Acad. Sci. U.S.A. 71, 3294–3298), with particles appearing at or above a tryptic insoluble peptide concentration of 4 mmol per mol phosphatidylcholine. In the present study, increasing concentrations of tryptic insoluble peptide were added to sonicated small unilamellar egg phosphatidylcholine vesicles and the rate of efflux of 22Na+ was examined by rapid (30 s) gel filtration on Sephadex G-50. Below a concentation of 3–5 mmol tryptic insoluble peptide/mol phosphatidylcholine, 22Na+ efflux occurs at a constant slow rate at given tryptic insoluble peptide concentrations. Above a concentration of 3–5 mM, the rate of efflux is biphasic at given tryptic insoluble peptide concentrations, exhibiting both an initial fast and a subsequent slow component. On the basis of graphic and computer curve-fitting analysis, with increasing tryptic insoluble peptide concentration, the rate of the slow component reaches a plateau at a tryptic insoluble peptide concentration of 3–5 mM and remains essentially constant until much higher concentrations are reached; the fast component increases linearly with increasing tryptic insoluble peptide concentration well beyond 5 mM. The most consistent interpretation of this data is as follows. The slow 22Na+ efflux component is due to perturbations of small unilamellar vesicle integrity by tryptic insoluble peptide monomers. At a tryptic insoluble peptide concentration of 3–5 mmol/mol, a critical concentration is reached following which there is intrabilayer tryptic insoluble peptide self-association. The fast 22Na+ efflux component is due to the increasing presence of tryptic insoluble peptide self-associated multimers the 80-Å particles seen by freeze-fracture electron microscopy) which results in a significantly larger bilayer defect than do tryptic insoluble peptide monomers. The failure of complete saturation of efflux by the fast component is ascribed to the presence of two populations of small unilamellar vesicles, some of which contain tryptic insoluble peptide multimers and some of which do not.Addition of cholesterol to the tryptic insoluble peptide/phosphatidylcholine vesicles decreases the rate of 22Na+ efflux by inhibiting primarily the fast component. Freeze-fracture electron microscopy indicates that the presence of cholesterol has no effect on the size, number or distribution of 80-Å intra-bilayer particles in the tryptic insoluble peptide/phosphatidylcholine vesicles. These results are consistent with a mechanism to explain the fast Na+ efflux component involving protein-lipid boundary perturbations.Efflux of 45Ca2+ from phosphatidylcholine vesicles is also enhanced by incorporation of tryptic insoluble peptide, but only if divalent cations (Ca2+ or Mg2+) are present in the external bathing media as well as inside the sonicated vesicles. If monovalent Na+ only is present in the bathing media no 45Ca2+ efflux is seen. Under conditions where 45Ca2+ efflux is seen, both a fast and a slow component are present, although both appear lower than corresponding rate constants for 22Na+ efflux. These results suggest a coordinated mechanism for ion efflux induced by tryptic insoluble peptide and, together with the 22Na+ efflux studies, may have mechanistic implications for the transbilayer phospholipid exchange (flip-flop) suggesed to be induced at glycophorin/phospholipid interfaces (de Kruiff, B., van Zoelen, E.J.J. and van Deenen, L.L.M. (1978) Biochim. Biophys. Acta 509, 537–542). 相似文献
59.
Henri Cappetta 《Geobios》1981,14(5):563-575
Recent researches in the phosphat-bearing basins ofMorocco have allowed to collect new selachian forms. In this paper, three Ypresian genera from Ouled Abdoun basin, new for Morocco, are described: Heptranchias howellii (Reed, 1946), Alopias denticulatus nov. sp. and Odontorhytis pappenheimiBöhm, 1926. The re-discovery of the genus Odontorhytis allows to state precisely its morphological dental features and to affirm that it is well a selachian and not a teleostean, as it was thought. The stratigraphic distribution of some species is stated precisely. 相似文献
60.
Cladocera and free-living Copepoda from the Fouta Djalon and adjacent mountain areas in West Africa 总被引:4,自引:4,他引:0
Henri J. Dumont 《Hydrobiologia》1981,85(2):97-115
Thirty-two species of Cladocera and 27 species of free-living copepods were identified in a series of samples collected in
25 localities in and around the Fouta Djalon mountains, West Africa. Beside great richness in numbers of species, the nature
of the fauna is noteworthy: at least 20% of the Cladocera and 50% of the copepods are endemic to West Africa. Possible palaeoclimatological
reasons for this are discussed. The cladoceran genus Streblocerus is recorded from Africa for the first time. It is an element of northern origin in the fauna of West Africa. More examples
of this kind are documented among the Copepoda Cyclopoida and Harpacticoida, but the bulk of the fauna is evidently of tropical
origin. In particular, great adaptive radiation is occurring in the local representatives of the genus Tropocyclops. Three new species of Parastenocaris are described; they are the first representatives of this genus found in West Africa. 相似文献