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81.
In the aquatic liverwort Riccia fluitans, the uptake of 14C-labeled 3-O-methyl glucose (3-OMG) and membrane depolarization (
m
) caused by different hexoses has been studied as a function of time and concentration of hexose, K+ and H+, respectively. The rate of uptake of the non-metabolized 3-OMG shows two components: (A)A pH-dependent saturable uptake with a km value around 0.1 mM which saturates at 2.1 and 7.2 mol G
DW
-1 h-1 at pH 6.8 and 5.0, respectively; and (B) a pH-insensitive uptake component which increases linearly with the external 3-OMG concentration and does not saturate 4 mM. Hexoses rapidly depolarize the plasmalemma of the thallus cell and increase its electrical conductance. The maximal
m
was 60±2 mV, the concentrations (mM) for half-maximal
m
were 0.24 glucose, 0.32 galactose, 0.37 2-deoxy glucose, 0.38 3-OMG, 0.57 mannose, and 34 fructose. In terms of a hexose carrier model and an equivalent circuit for the hexose-induced depolarized state of the membrane, it is proposed that a hexose carrier operates either electrogenically in its protonated, pH-and voltage-sensitive state, or by transmembrane diffusion of its uncharged state.Symbols and Abbreviations
m
membrane potential (mV)
-
g
m
membrane (slope) conductance (Sm-2)
- 3-OMG
3-O-methyl glucose 相似文献
82.
83.
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
84.
85.
For Calliphora the wingbeat frequency and the underlying motoneuronal activity were recorded during adult life. Wingbeat frequency increases during the ten days following last molt. The activity of motoneurons serving four selected flight muscles (nonfibrillar and fibrillar ones) also increases with age. The motoneuronal activity of young and old flies was analyzed statistically (serial and cross-correlograms, latency and phase histograms). In addition, several wing manipulations were carried out to evaluate the significance of sensory feedback on pattern generation during maturation. These ontogenetic studies suggest a centrally generated motor pattern that (1) is essentially complete with the molt to adulthood, (2) shows a progressive increase in intrinsic activity, and (3) is modulated by sensory feedback from the wing region by the same amount irrespective of age. Similarities in the postlarval development of the flight pattern of neurogenic and myogenic flyers are discussed. 相似文献
86.
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
87.
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
88.
89.
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
90.
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