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731.
A F Wright 《BMJ (Clinical research ed.)》1982,285(6342):609-611
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Carbon and nitrogen stable isotope analyses have improved our understanding of food webs and movement patterns of aquatic
organisms. These techniques have recently been applied to diet studies of elasmobranch fishes, but isotope turnover rates
and isotope diet–tissue discrimination are still poorly understood for this group. We performed a diet switch experiment on
captive sandbar sharks (Carcharhinus plumbeus) as a model shark species to determine tissue turnover rates for liver, whole blood, and white muscle. In a second experiment,
we subjected captive coastal skates (Leucoraja spp.) to serial salinity reductions to measure possible impacts of tissue urea content on nitrogen stable isotope values.
We extracted urea from spiny dogfish (Squalus acanthias) white muscle to test for effects on nitrogen stable isotopes. Isotope turnover was slow for shark tissues and similar to
previously published estimates for stingrays and teleost fishes with low growth rates. Muscle isotope data would likely fail
to capture seasonal migrations or diet switches in sharks, while liver and whole blood would more closely reflect shorter
term movement or shifts in diet. Nitrogen stable isotope values of skate blood and skate and dogfish white muscle were not
affected by tissue urea content, suggesting that available diet–tissue discrimination estimates for teleost fishes with similar
physiologies would provide accurate estimates for elasmobranchs. 相似文献
736.
Topography of the C terminus of cytochrome b5 tightly bound to dimyristoylphosphatidylcholine vesicles 总被引:1,自引:0,他引:1
Cytochrome b5 holoenzyme was bound asymmetrically in the tightly bound form to small unilamellar dimyristoylphosphatidylcholine vesicles. [3H]Taurine, a membrane-impermeant nucleophile, was added to the external medium and was then cross-linked to cytochrome carboxyl residues by the addition of a water-soluble carbodiimide. Nonpolar peptide was isolated after trypsin digestion of taurine-labeled apocytochrome b5 and contained 1.7-1.9 residues of taurine. The C-terminal tetrapeptide containing residues Thr130-Asn133 was generated by chymotryptic hydrolysis of radiolabeled nonpolar peptide and was purified by gel filtration and ion exchange chromatography. Amino acid analysis of the C-terminal tetrapeptide showed that about 1.6 mol of taurine was cross-linked per mol of peptide. When the experiment was performed with taurine trapped inside the vesicles, no cross-linking was observed. The results suggest that when cytochrome b5 holoenzyme is bound to vesicles in the tight binding form, the C terminus is located on the external surface of the vesicles. 相似文献
737.
S Sayama R V Iozzo G S Lazarus N M Schechter 《The Journal of biological chemistry》1987,262(14):6808-6815
The subcellular localization of human skin chymase to mast cell granules was established by immunoelectron microscopy, and binding of chymase to the area of the dermo-epidermal junction, a basement membrane, was demonstrated immunocytochemically in cryosections incubated with purified proteinase prior to immunolabeling. Because heparin and heparan sulfate proteoglycans are major constituents of mast cell granules and basement membranes, respectively, the ability of chymase to bind to glycosaminoglycans (GAG) was investigated. Among a variety of GAGs, only binding of chymase to heparin and heparan sulfate appears physiologically significant. Binding was ionic strength-dependent, involved amino groups on the proteinase, and correlated with increasing GAG sulfate content, indicating a predominantly electrostatic association. Interaction with heparin was observed in solutions containing up to 0.5 M NaCl, and interaction with heparan sulfate was observed in solutions containing up to 0.3 M NaCl. Binding of heparin did not detectably affect catalysis of peptide substrates, but may reduce accessibility of proteinase to protein substrates. Measurements among a series of serine class proteinases indicated that heparin binding was a more common property of mast cell proteinases than proteinases stored in other secretory granules. Binding of chymase to heparin is likely to have a storage as well as a structural role within the mast cell granule, whereas binding of chymase to heparan sulfate may have physiological significance after degranulation. 相似文献
738.
Sylvester J. T.; Harabin A. L.; Peake M. D.; Frank R. S. 《Journal of applied physiology》1980,49(5):820-825
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