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21.
Wolfang Zeiske Heinz Marin 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1992,162(4):340-344
Summary Chloride-stimulated K+ secretion by Manduca sexta midgut (5th-instar larvae) was measured as K+-carried short-circuit current of the tissue mounted in an Ussing chamber. Microscopic parameters, such as single-channel current and channel density for the rate-determining passive transport step across the basolateral goblet cell membrane (i.e. K+ channels), were estimated by means of current-fluctuation analysis of the K+ channel blockade by haemolymph-side Ba2+ ions. Ba2+ was equally effective with Cl- or gluconate (Glu-) as the principal ambient anion. The Ba2+-induced K+ channel conduction noise is reflected by a Lorentzian, or relaxation, noise component in the power spectrum of the K+ current fluctuations. A reduced Lorentzian plateau value, but an unchanged corner frequency, were observed when Cl- was replaced by Glu-. The results from the analysis of a two-state model of K+ channel block by Ba2+, with respect to the anion-replacement effects, suggest that the observed changes in K+ current and Lorentzian plateau value mirror a complex change of the underlying parameters: Cl- omission reduces single channel current but increases channel density so that the product of single channel current and channel density is smaller in Glu- than in Cl-. It seems likely that basolateral K+ channels (1) are subject to anionic gating ligands, and (2) depend on anions with respect to the rate of K+ transfer through and open K+ channel.Abbreviations a.c.
alternating current
-
single-channel conductance
-
E
K
K+ Nernst potential
-
f
frequency contained in current noise
-
f
c
corner frequency
- Glu-
gluconate
-
G
t
transepithelial conductance
-
I
sc
short-circuit current
-
I
K
K+ current
-
I
K(max)
maximal K+ current
-
i
single-channel current
-
K
Ba
barium inhibition constant
-
K
m
Michaelis constant of saturating K+ current
-
k
01 and k
10
barium association and dissociation rate constant, respectively
-
M
K+ channel density
-
S
f
power density
-
S
o
Lorentzian plateau value
-
P
o
channel-open probability
-
P
K
K+ permeability
-
V
sc
cellular potential at short-circuit
These results have already been presented in part, at the 1989 joint meeting of the German and Israel Physiological Societies in Jerusalem (Zeiske et al. 1990). 相似文献
22.
C. Brugidou A. Rocher E. Giraud B. Lelong B. Marin M. Raimbault 《Biotechnology Techniques》1991,5(6):475-478
A new technique for separation and determination of ATP, ADP, AMP, NAD+, NADP+, NADH and NADPH in Lacwbacillus plantarum has been developped. It involves acid and basic extraction of nucleotide pool, analysis by reverse-phase high performance liquid chromatography on a 5 m Spherisorb ODS-1 column and UV detection. The method offers advantages in accurate estimations of adenylic and nicotinamide nucleotides concentrations in Lactobacillus plantarum during the growth phase. Such results indicate the potential of this technique as an important research tool. 相似文献
23.
Summary The role and importance of the redox potential phenomena in submerged citric acid production are discussed. The redox potential of the fermentation broth is the result of oxydo-reduction processes where the metabolic activity of the microorganism Aspergillus niger plays the most significant role. The course of the redox curve for a good yielding citric acid production is presented and interpreted. The experiments of submerged citric acid production were carried out on beet molasses treated with potassium hexacyanoferrate and inoculated with A. niger spores. 相似文献
24.
Inhibition of the ATPase by inorganic phosphate, Pi, was examined in terms of product inhibition of the various activities catalyzed by an enzyme preparation from rat brain, and considered in terms of the specific transport processes of the membrane Na+,K+-pump that these activities reflect. The K+-dependent phosphatase activity of the enzyme was most sensitive to Pi, and inhibition was competitive toward the substrate, nitrophenyl phosphate, as would be expected if Pi were released from the same enzyme form that bound substrate. However, this enzymatic activity does not seem to represent a transport process, and thus a cyclical discharge of K+ may not be involved. The Na+-dependent exchange activity was unaffected by Pi, in accord with the absence of Pi release in the reaction sequence. For the corresponding Na+/Na+ exchange function of the pump, which reportedly does not involve ATP hydrolysis either, prior release of Pi obviously cannot be required for Na+ discharge. With the Na+-dependent ATPase activity, measured using micromolar concentrations of ATP, Pi inhibited, but far less than with the phosphatase activity, and inhibition was not competitive toward ATP. Moreover, inhibition decreased as the Na+ concentration was raised from 10 to 100 mM. This elevated concentration of Na+ also led to substrate inhibition. For this ATPase activity, and the corresponding transport process, uncoupled Na+ efflux, the findings suggest that Na+ discharge follows Pi release, in contrast to Na+/Na+ exchange. The ATPase activity, measured with millimolar concentrations of ATP and reflecting the coupled Na+,K+-transport function, was similarly sensitive to Pi, and again inhibition was not competitive toward ATP. However, in this case inhibition did not increase as the Na+ concentration was lowered. For this activity, and the associated transport process, the site of Na+ discharge in the overall reaction sequence remains unresolved. 相似文献
25.
Frederick T. Marin 《Developmental biology》1976,48(1):110-117
Evidence is presented which indicates that amino acid starvation is the specific stimulus initiating the developmental phase of the life cycle of Dictyostelium discoideum: (i) Amoebae were washed free of complex growth medium and placed in buffer supplemented with specific nutrients; amino acids were the only nutrients that specifically inhibited the initiation of development. (ii) A partially defined growth medium allowing selective starvation for amino acids or glucose during growth is described. Amoebae initiated development only when starved for amino acids. Any effect of glucose on the primary control of the initiation of development is an indirect result of its utilization as a source of precursors for endogenously synthesized amino acids. 相似文献
26.
Thierry Brun Jean Péduzzi Manuela Marin Caniça Gérard Paul Pierre Névot Michel Barthélémy Roger Labia 《FEMS microbiology letters》1994,120(1-2):111-117
Abstract A novel procedure was used to purify a cytosolic chitinase from Candida albicans to electrophoretic homogeneity. The results represent the first demonstration of the purification of a fungal intracellular chitinase using the criterion of a single band detected following silver-staining of a polyacrylamide gel run under denaturing conditions. Purified chitinase had pH and temperature optima of 5.0 and 50°C, respectively. Inhibition of enzyme activity by allosamidin was pH-dependent occuring maximally at pH 8.0. Phospholipids had similar marked and highly specific effects on the activities of both the purified soluble enzyme and a solubilized microsomal chitinase from C. albicans . Evidence is provided for the existence of a complex chitinolytic system in this organism. 相似文献
27.
In this paper, the authors study the correlation which exists between somatic development, represented by weight, height and thorax, and the age of onset of menarche. The results indicate that girls showing early menarche have a somatic development greater than the mean. It has also been possible to show that the greatest increase in height occurs before the menarche, while the greatest increase in weight coincides with the appearance of the menarche, or occurs shortly afterwards. 相似文献
28.
Johanna Marin‐Carbonne Vincent Busigny Jennyfer Miot Claire Rollion‐Bard Elodie Muller Nadja Drabon Damien Jacob Sylvain Pont Martin Robyr Tomaso R. R. Bontognali Camille Franois Stephanie Reynaud Mark Van Zuilen Pascal Philippot 《Geobiology》2020,18(3):306-325
On the basis of phylogenetic studies and laboratory cultures, it has been proposed that the ability of microbes to metabolize iron has emerged prior to the Archaea/Bacteria split. However, no unambiguous geochemical data supporting this claim have been put forward in rocks older than 2.7–2.5 giga years (Gyr). In the present work, we report in situ Fe and S isotope composition of pyrite from 3.28‐ to 3.26‐Gyr‐old cherts from the upper Mendon Formation, South Africa. We identified three populations of microscopic pyrites showing a wide range of Fe isotope compositions, which cluster around two δ56Fe values of ?1.8‰ and +1‰. These three pyrite groups can also be distinguished based on the pyrite crystallinity and the S isotope mass‐independent signatures. One pyrite group displays poorly crystallized pyrite minerals with positive Δ33S values > +3‰, while the other groups display more variable and closer to 0‰ Δ33S values with recrystallized pyrite rims. It is worth to note that all the pyrite groups display positive Δ33S values in the pyrite core and similar trace element compositions. We therefore suggest that two of the pyrite groups have experienced late fluid circulations that have led to partial recrystallization and dilution of S isotope mass‐independent signature but not modification of the Fe isotope record. Considering the mineralogy and geochemistry of the pyrites and associated organic material, we conclude that this iron isotope systematic derives from microbial respiration of iron oxides during early diagenesis. Our data extend the geological record of dissimilatory iron reduction (DIR) back more than 560 million years (Myr) and confirm that micro‐organisms closely related to the last common ancestor had the ability to reduce Fe(III). 相似文献
29.
Sara Marin Anaïs Gibert Juliette Archambeau Vincent Bonhomme Mylne Lascoste Benoit Pujol 《Molecular ecology》2020,29(16):3010-3021
Phenotypic divergence among natural populations can be explained by natural selection or by neutral processes such as drift. Many examples in the literature compare putatively neutral (FST) and quantitative genetic (QST) differentiation in multiple populations to assess their evolutionary signature and identify candidate traits involved with local adaptation. Investigating these signatures in closely related or recently diversified species has the potential to shed light on the divergence processes acting at the interspecific level. Here, we conducted this comparison in two subspecies of snapdragon plants (eight populations of Antirrhinum majus pseudomajus and five populations of A. m. striatum) in a common garden experiment. We also tested whether altitude was involved with population phenotypic divergence. Our results identified candidate phenological and morphological traits involved with local adaptation. Most of these traits were identified in one subspecies but not the other. Phenotypic divergence increased with altitude for a few biomass‐related traits, but only in A. m. striatum. These traits therefore potentially reflect A. m. striatum adaptation to altitude. Our findings imply that adaptive processes potentially differ at the scale of A. majus subspecies. 相似文献
30.