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A new, easy method to produce and calibrate a 1-μm tip intracellular pH electrode is described. This antimony electrode and a micro-calomel electrode were inserted into the giant axon of Loligo pealii. The potential obtained when the axon was bathed in seawater corresponded to a pH of 7.0 ± 0.2. It was found that acidification of the external perfusate induced a drop in axoplasmatic pH leading to changes in the membrane electrical properties. Changes of resting or action potentials did not influence intracellular pH.  相似文献   

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Lysosomal activation was induced in dog kidney and HEp-2 cells by treatment with anticellular serum and high concentrations (20 μg/ml) of vitamin A alcohol. The morphological changes accompanying the release of enzymes from activated lysosomes were described. Measurements of cell coat thickness by ellipsometry revealed that lysosomal enzymes released extracellularly were able to digest the coat. The scale of enzyme release was an important factor in determining the amount of coat digested. Complement-sufficient anticellular sera and high concentrations of vitamin A induced marked lysosomal activation and extensive digestion of the coat. Complement-deficient anticellular serum produced significantly less lysosomal labilization and only limited digestion of the coat. The digestion of the cell coat induced by these agents was prevented by pretreatment of the cells with either hydrocortisone or chloroquine.  相似文献   

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The quinacrine mustard fluorescence patterns of the metaphase chromosomes of different tissues of the same plant species were found to be identical. Similar studies of the chromosome regions on human material gave the same result.  相似文献   

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Reaction of trifluoro(fluoroxy)methane at ca. −80° with 3,4,6-tri-O-acetyl-D-galactal affords trifluoromethyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-α-D-galactopyranoside (2, 39%), 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-α-D-galactopyranosyl fluoride (3, 37%), trifluoromethyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-α-D-talopyranoside (4, 3%), and 3,4,6-tri-O-acetyl-2-deoxy-2-fluor-α-D-talopyranosyl fluoride (5, 2%). The structures of compounds 25 have been established by n.m.r. spectroscopy. Acid hydrolysis of 2 or 3 allords 2-deoxy-2-fluoro-D-galactose.  相似文献   

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Deletion mutants and substitution mutants of bacteriophage λ have been used to examine the physical structure of the attφ site in the λ chromosome which is essential for prophage integration. Integration-defective att mutants were analyzed by constructing heteroduplex DNA molecules containing one wild-type and one mutant strand and examining these heteroduplexes by electron microscopy. The results indicate that attφ is less than 2500 base pairs in length and may be as small as 20 to 50 base pairs. Integration cross-overs between attφ and its bacterial analog, attB, occur within a region which is less than 12 base pairs in length. Moreover, there is no detectable base sequence homology between attφ and attB. These results suggest that λ integration is a truly unique system of recombination.  相似文献   

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The genomes of many species are crowded with repetitive mobile sequences. In the case of endogenous retroviruses (ERVs) there is, for various reasons, considerable confusion regarding names assigned to families/groups of ERVs as well as individual ERV loci. Human ERVs have been studied in greater detail, and naming of HERVs in the scientific literature is somewhat confusing not just to the outsider. Without guidelines, confusion for ERVs in other species will also probably increase if those ERVs are studied in greater detail. Based on previous experience, this review highlights some of the problems when naming and classifying ERVs, and provides some guidance for detecting and characterizing ERV sequences. Because of the close relationship between ERVs and exogenous retroviruses (XRVs) it is reasonable to reconcile their classification with that of XRVs. We here argue that classification should be based on a combination of similarity, structural features, (inferred) function, and previous nomenclature. Because the RepBase system is widely employed in genome annotation, RepBase designations should be considered in further taxonomic efforts. To lay a foundation for a phylogenetically based taxonomy, further analyses of ERVs in many hosts are needed. A dedicated, permanent, international consortium would best be suited to integrate and communicate our current and future knowledge on repetitive, mobile elements in general to the scientific community.  相似文献   

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Methyl α-D- (1) and methyl β-D-glucofuranosidurono-6,3-lactone (5) were oxidized at C-2 or C-5, 1,2-O-isopropylidene-α-D- (10) and 1,2-O-cyclohexylidene-α-D-glucofuranurono-6,3-lactone (11) at C-5 by various methods to the corresponding D-arabino- or D-xylo-hexulofuranosiduronolactones. In contrast to the starting materials 5, 10, and 11, the 5-uloses 15, 17, and 18 do not exhibit reducing power in alkaline Cu2+ solutions. Methyl 5-O-benzyl-α-D- and methyl 5-O-benzyl-β-D-arabino-2-hexulofuranosidurono-6,3-lactone reduce Benedict solution at room temperature.  相似文献   

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For beta-amylolysis, the number of bonds split per effective enzyme-substrate encounter has been determined with amyloses having various degrees of polymerization (d.p.), labelled with 14C. The degradation is shifted in the direction of the “single chain mechanism” with increasing d.p. By taking into account the “inactive, non-reacting” collisions leading to “self-inhibition”, the number of bonds split per “reactive” and “non-reactive” enzyme-substrate encounter was established. From these data, and from the inhibition constant of the inner D-glucose residues of the amylose chain, in conjunction with the Michaelis constant extrapolated to d.p.  4, the actual rate constants for the formation and dissociation of the “reactive” enzyme-substrate complexes and for the formation and dissociation of the “non-reactive” enzyme-substrate complexes were determined. It was found that the rate constants for the formation of the “reactive” complexes decrease slowly with the increase of “self-inhibition”, whereas those for the dissociation of these complexes decrease to a greater extent.  相似文献   

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1. The aim of these studies was to determine metabolic changes in the liver accompanying the decreased in blood ketone body content that follows administration of a glucocorticoid to a ketotic cow. Accordingly, the hepatic metabolism of ketotic cows given a therapeutic dose of Voren (dexamethasone 21-isonicotinate) 48 h previously, was compared with that of untreated ketotic cows.  相似文献   

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Initial X-ray diffraction studies of large single crystals of yeast hexokinase-B provide information on its subunit structure and show the crystals to be suitable for a high resolution structure determination. Patterson maps of the native protein crystals suggest that the two 50,000 molecular weight subunits are identical, or very nearly so, and that they are related by an approximate rather than a true diad axis; that is, one subunit is translated relative to the other by 3.6 Å along the molecular symmetry axis. This results in heterologous subunit interactions rather than the isologous interactions expected.  相似文献   

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Acid-catalyzed dehydration of methyl and ethyl 2-methyl-5-(d-arabino-tetrahydroxybutyl)-3-furoate (4a, b) takes place preferentially with inversion of configuration at C-1′, yielding the corresponding 5-(1,4-anhydro-d-ribo-tetrahydroxybutyl)-2-methyl-3-furoate (6a, b), and, to a much smaller extent, with retention of configuration giving the isomeric d-arabino anhydro-derivative (5a, b). The reaction is reversible, the equilibrium being set up when there is a high concentration of the thermodynamically more-stable d-ribo anhydro-derivative in the presence of the d-arabino isomer, the starting (d-arabino-tetrahydroxybutyl)furan (4a, db), and a compound thought to be methyl (or ethyl) 2-methyl-5-(d-ribo-tetrahydroxybutyl)-3-furoate (13). A mechanism is proposed for this reaction which involves the C-1′ carbonium ion 15 as the key intermediate. The anhydro derivatives of the d-ribo and d-arabino configurations can be distinguished by their optical rotations, the chemical shifts of H-1′, and the J1′,2′ coupling constants.  相似文献   

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