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1.
A simple theoretical model is presented for simulating the self-sustained oscillations of electric potential and pH at an oil/water interface appearing in a two-phase system composed of 2-nitropropane solution containing picrate acid and an aqueous solution of cetyltrimethylammonium bromide. In the present model, a well-known condition necessary for the occurrence of self-sustained oscillations, i.e., the presence of a positive feedback process far from equilibrium, is taken into account in a set of kinetic equations to describe simplified characters of the following two processes: (i) a cooperative formation of ion pair complexes at the interface, and (ii) supply of picrate anions and cetyltrimethylammonium cations to the interface accompanied by release of ion pair complexes to the organic phase. The numerical solutions of the present equations are shown to reproduce fairly well the characteristic properties of the oscillation of electric potential and pH such as wave forms and frequencies. 相似文献
2.
Changes in membrane electric potential in response to taste substances were studied for membranes containing differing amounts of negatively charged lipids in the membrane matrix of polyvinyl chloride and plasticizer. Responses to quinine showing bitterness decreased systematically with increasing the quantity of charged lipids contained in the membrane, whereas the response did not depend on differences in the hydrocarbon chains of lipids. The mechanism is discussed qualitatively in terms of hydrophobicity and hydrophilicity of the membranes. 相似文献
3.
The relationship between gravitropism and surface electrical potentials was studied using etiolated epicotyls of adzuki bean (Phaseolus angularis). Early downward curvature (or transient positive gravitropic response) was observed about 1 min after gravistimulation. The downward curvature was closely related to the speed of the subsequent upward curvature. Surface electrical potentials decreased cooperatively in a limited region on the upper side within only 0.5 to 2 min. This is the earliest event found so far to follow gravistimulation of intact epicotyls. The rapid change in the potential had a high correlation with the early downward curvature and also the subsequent negative gravitropism. It is suggested that the rapid potential change plays an important role in gravity perception. 相似文献
4.
Ordered-fluid phase transitions of methylphosphatidic and phosphatidic acid bilayers are discussed theoretically to explain comprehensively various observed data in the presence of Ca2+ or protons. It is shown that the observed data can be explained reasonably by taking account of the interaction among neighboring head-groups with the aid of Ca2+ or protons. As a result, a quantitative explanation is given for the dependence of the phase-transition temperature on pH as well as Ca2+ concentration with the coexistence of monovalent cations. The dependence of the cooperativity of the transition on pH and monovalent cation concentration is also well explained. It is also pointed out that in the ordered-fluid phase transitions, a hysteresis metastable state and phase separation can be expected to appear under some conditions. 相似文献
5.
Elevational species richness gradients in a hyperdiverse insect taxon: a global meta‐study on geometrid moths
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Jan Beck Christy M. McCain Jan C. Axmacher Louise A. Ashton Florian Bärtschi Gunnar Brehm Sei‐Woong Choi Oldrich Cizek Robert K. Colwell Konrad Fiedler Cristina L. Francois Steven Highland Jeremy D. Holloway Jurie Intachat Tomas Kadlec Roger L. Kitching Sarah C. Maunsell Thomas Merckx Akihiro Nakamura Erica Odell Weiguo Sang Pagi S. Toko Jaroslav Zamecnik Yi Zou Vojtech Novotny 《Global Ecology and Biogeography》2017,26(4):412-424
6.
A band-type alternating pattern of acidic and alkaline regions formed along the Characean cell wall is discussed theoretically. The model system is constructed from linear diffusion equations for the concentration of H+ outside the internode and in the protoplasm. The plasmalemma is taken as a boundary transporting H+ under energy supply by light. The sizes of the protoplasm and extracellular water phase are taken into account explicitly in the present model system to reproduce qualitatively the characteristics observed in various types of experiments. Theoretical analysis shows that the band pattern belongs to dissipative structures emerging far from equilibrium, and is stabilized through the electric current loops produced by locally activated electrogenic H+ pumps and spatially separated passive H+ influx (or OH- efflux) across the membrane. Both the numerical calculation and the theoretical analysis using a generalized time-dependent Ginzburg-Landau equation reveal the following points: (i) the intemodal cell with a larger vacuole in a smaller size of the extracellular water phase tends to exhibit a clearer band pattern; (ii) the increase in viscosity of the external aqueous medium makes the bands appear more easily and, furthermore, distinctly; (iii) the change in size of the extracellular water phase significantly affects the kinetics of the pattern- formation process. These results are interpreted reasonably by taking account of the electric current circulating between the acidic and alkaline regions. 相似文献
7.
Toko Tanikawa Yasuhiro Hirano Masako Dannoura Keitarou Yamase Kenji Aono Masahiro Ishii Tetsurou Igarashi Hidetoshi Ikeno Yoichi Kanazawa 《Plant and Soil》2013,373(1-2):317-327
Aim
Ground-penetrating radar (GPR) has been applied to detect coarse tree roots. The horizontal angle of a root crossing a scanning line is a factor that affects both root detection and waveform parameter values. The purpose of this study was to quantitatively evaluate the influence of root orientation (x, degree) on two major waveform parameters, amplitude area (A, dB × ns) and time interval between zero crossings (T, ns).Methods
We scanned four diameter classes of dowels in a sandy bed as simulated roots using a 900 MHz antenna from multiple angles to clarify the relationships between the parameters and x.Results
Angle x strongly affected reflection images and A values. The variation in A(x) fitted a sinusoidal waveform, whereas T was independent of x. The value of A scanning at 90° was estimated by A values of arbitrary x in two orthogonal transects. The sum of T in all reflected waveforms showed a significant linear correlation with dowel diameter.Conclusions
We clarified that root orientation dramatically affected root detection and A values. The sum of T of all reflected waveforms was a suitable parameter for estimating root diameter. Applying grid transects can overcome the effects of root orientation. 相似文献8.
Kosono S Kajiyama Y Kawasaki S Yoshinaka T Haga K Kudo T 《Biochimica et biophysica acta》2006,1758(5):627-635
ShaA, a member of a multigene-encoded Na+/H+ antiporter in B. subtilis, is a large integral membrane protein consisting of 20 transmembrane helices (TM). Conservation of ShaA-like protein subunits in several cation-coupled enzymes, including the NuoL (ND5) subunit of the H+-translocating complex I, suggests the involvement of ShaA in cation transport. Bacillus subtilis ShaA contains six acidic residues that are conserved in ShaA homologues and are located in putative transmembrane helices. We examined the functional involvement of the six transmembrane acidic residues of ShaA by site-directed mutagenesis. Mutation in glutamate (Glu)-113 in TM-4, Glu-657 in TM-18, aspartate (Asp)-734 and Glu-747 in TM-20 abolished the antiport activity, suggesting that these residues play important roles in the ion transport of Sha. The acidic group was necessary and sufficient in Glu-657 and Asp-743, while it was not true of Glu-113 and Glu-747. Mutation in Asp-103 in TM-3, which is conserved in ShaA-types but not in ShaAB-types, partially affected on the antiport activity. Mutation in Asp-50 in TM-2 resulted in a unexpected phenotype: mutants retained the wild type level of ability to confer NaCl resistance to the Na+/H+ antiporter-deficient E. coli KNabc, but showed a very low antiport activity. The acidic group of Asp-50 and Asp-103 was not essential for the function. Our results suggested that these acidic residues are functionally involved in the ion transport of Sha, and some of them probably in cation binding and/or translocation. 相似文献
9.
Naito AT Sumida T Nomura S Liu ML Higo T Nakagawa A Okada K Sakai T Hashimoto A Hara Y Shimizu I Zhu W Toko H Katada A Akazawa H Oka T Lee JK Minamino T Nagai T Walsh K Kikuchi A Matsumoto M Botto M Shiojima I Komuro I 《Cell》2012,149(6):1298-1313
Wnt signaling plays critical roles in development of various organs and pathogenesis of many diseases, and augmented Wnt signaling has recently been implicated in mammalian aging and aging-related phenotypes. We here report that complement C1q activates canonical Wnt signaling and promotes aging-associated decline in tissue regeneration. Serum C1q concentration is increased with aging, and Wnt signaling activity is augmented during aging in the serum and in multiple tissues of wild-type mice, but not in those of C1qa-deficient mice. C1q activates canonical Wnt signaling by binding to Frizzled receptors and subsequently inducing C1s-dependent cleavage of the ectodomain of Wnt coreceptor low-density lipoprotein receptor-related protein 6. Skeletal muscle regeneration in young mice is inhibited by exogenous C1q treatment, whereas aging-associated impairment of muscle regeneration is restored by C1s inhibition or C1qa gene disruption. Our findings therefore suggest the unexpected role of complement C1q in Wnt signal transduction and modulation of mammalian aging. 相似文献
10.
Tomohei Nakao Hiroko Fukushima Takashi Fukushima Ryoko Suzuki Sho Hosaka Yuni Yamaki Chie Kobayashi Atsushi Iwabuchi Kazuo Imagawa Aiko Sakai Toko Shinkai Kouji Masumoto Shingo Sakashita Tomohiko Masumoto Masashi Mizumoto Ryo Sumazaki Hideyuki Sakurai 《Reports of Practical Oncology and Radiotherapy》2018,23(5):442-450