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81.
Hubert Felle 《生物化学与生物物理学报:生物膜》1980,602(1):181-195
Green thallus cells of the aquatic liverwort, Riccia fluitans, are rapidly depolarized in the presence of 1–20 μM NH4Cl and 5–100 μM CH3NH3Cl, respectively. Simultaneously, the membrane conductance is increased from 0.41 to 1.2 S · m?2. Uptake of [14C]methylamine is stimulated by increasing [K+]o and inhibited by increasing [Na+]o or [H+]o, is highly voltage sensitive, and saturates at low amine concentrations.Double-reciprocal plots of (a) maximal membrane depolarization and (b) methylamine uptake vs. external amine concentration give apparent Km values of 2 ± 1 μM ammonia and 25–50 μM methylamine; Km values for changes in conductance and membrane current are greater and voltage dependent. Whereas the amine transport into the cell is strongly inhibited by CN?, the amine efflux is stimulated.The current-voltage characteristics of the ammonia transport are represented by a sigmoid curve with an equilibrium potential of ?60 mV, and this is understood as a typical carrier curve with a saturation current of about 70 mA · m?2. It is further concluded that the evidently carrier-mediated transport is competitive for the two amines tested, and that ammonia and methylamine are transported in the protonated form as NH4+ and CH3NH3+ into the cytoplasm. 相似文献
82.
83.
Variations in aspartasic activity in various media are due to aspartate-ammonium lyase induction and to regulation of the biosynthesis of this enzyme. Evidence for neosynthesis of the enzyme is provided by labelling and separation of the protein. The inducer appears to be aspartic acid. The biosynthesis is subject to pronounced catabolic repression. The physiological function of aspartate-ammonium lyase is discussed. 相似文献
84.
Dr. Jack E. Brinn Hubert W. Burden Michael R. Schweisthal 《Cell and tissue research》1977,182(1):133-138
Summary The fetal rat pancreas, explanted at 18 days of gestation and cultured up to ten days, contains numerous acetylcholinesterase-positive neurons. These nerves usually appear in small ganglia although single nerve cells are encountered. The axons of these intrapancreatic nerves appear to terminate only in the islet tissue and not on any exocrine components of the expiant. It is concluded that the fetal rat pancreas contains an islet-specific group of cholinergic neurons.We gratefully acknowledge the skilled technical assistance of Dan Whitehead and the secretarial assistance of Mary Pat Brady 相似文献
85.
86.
Hubert G. Theuns Jan E.G. van Dam Jan M. Luteijn Cornelis A. Salemink 《Phytochemistry》1977,16(6):753-755
Three new alkaloids have been identified from Papaver bracteatum, 14-β-hydroxycodeinone, 14-β-hydroxycodeine and N-methylcorydaldine. The presence of alpinigenine was also confirmed. 相似文献
87.
Juan C. Slebe Roman Herrera Elizabeth Hubert Alicia Ojeda Ricardo B. Maccioni 《The protein journal》1983,2(6):437-443
Selective treatment of pig kidney fructose 1,6-bisphosphatase with potassium cyanate leads to the formation of an active carbamylated enzyme that has lost the cooperative interactions among AMP sites, but retains sensitivity to inhibition of catalytic activity by the regulator AMP. Incorporation data on [14C]KNCO indicate that the loss of enzyme cooperativity at the AMP sites is related to selective carbamylation of four lysine residues per mole of tetrameric enzyme. Exhaustive carbamylation suggests that a second lysine residue per subunit is essential for AMP inhibition. 相似文献
88.
New shuttle vectors for Clostridium acetobutylicum were constructed, using as replicons the Gram-positive plasmid pIM13, and derivatives of the Gram-negative plasmid pBR322, including pUC19. These vectors transformed C. acetobutylicum at a high frequency (up to 10(6) transformants per microgram DNA) by PEG-mediated protoplast transformation. A mutant host strain, NI-4082, was isolated on the basis of its ability to maintain plasmid pIM13 stably in the absence of selection pressure. The shuttle vectors showed no segregational or structural instability in this mutant strain. Moreover, the results suggested a relationship between segregational instability and the multimerization of pIM13 in C. acetobutylicum. The host/vector system described possessed all the properties required for efficient gene cloning in this species. 相似文献
89.
Cell-wall acidification and electrical reactions (depolarization and hyperpolarization) are typical auxin responses in maize (Zea mays L.) coleoptiles. In an attempt to test the role of the outer epidermis in these responses, they have been measured and compared in intact and peeled coleoptile fragments. To exclude interactions between parenchymal and epidermal cells, the coleoptile pieces were completely stripped of their outer epidermis. This preparation was monitored by means of a scanning electron microscope. When externally applied indole-3-acetic acid was tested, we found that neither cell-wall acidification nor the electrical membrane responses depended on the presence of intact epidermal cells.Abbreviations IAA
Indole-3-acetic acid
- MES
2-[N morpholino-ethane-sulfonic acid
- TRIS
2-Amino-2-hydroxymethyl-1,3-propanediol
We thank Kuki Kaethner for her excellent technical assistance. This work was supported by the Hessische Graduiertenförderung and the Deutsche Forschungsgemeinschaft. 相似文献
90.
Hubert F. Loyke 《Biological trace element research》1992,33(1-3):129-133
With reports of either no change or reduction of blood pressure, the relationship between selenium and blood pressure has
not been clear. Normal Se values are not available for the Sprague Dawley (SD) rat or in the young and adult rat with various
models of experimental hypertension. This study measured serum Se levels in the young and adult normotensive (NT), Grollman
renal hypertensive (RH), and Okamoto-Aoki spontaneous hypertensive rats (SHR). The young animals have statistically significant
(P<0.001) lower Se values as measured by the fluorometric method than those found at adulthood. Selenium levels were found to
be altered in the adult SHR animals when compared with the RH and NT animals. The serum Se value for the normotensive SD rat
was found to be 65.0±3.5 μg/dL, and for the two experimental models, 63.7±4.6 μg/dL for the RH, whereas the SHR level was
elevated to 75.04±4.8 μg/dL (P<0.001). Elevated serum Se values in the adult SHR animals suggests an altered metabolism in SHR animals. 相似文献