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31.
A. D. Ryabov Yulia N. Firsova Aleksei Y. Ershov Ilia A. Dementiev 《Journal of biological inorganic chemistry》1999,4(2):175-182
Glucose oxidase-catalyzed reduction of cis[MIII (LL)2Cl2]+ (M=Os and Ru) complexes to cis[MII (LL)2Cl2] (LL=2,2′-bipyridine and 1,10-phenanthroline type ligands) by d-glucose is a first-order process in the complex and the enzyme in aqueous buffered solution. The reaction follows MichaelisMenten
kinetics in d-glucose and the rate is independent of d-glucose concentration above 0.03 M. The reactivity decreases in the series [Ru(bpy)2Cl2]+ > [Os(phen)2Cl2]+ > [Os(4,4′-Me2bpy)2Cl2]+ > [Os(4,7Me2phen)2Cl2]+. The measured second-order rate constant for the oxidation of reduced glucose oxidase by [Os(phen)2Cl2]+ in air equals 1.2×105 M–1 s–1 at pH 6.7, [d-glucose] 0.05 M, and 25 °C, which is ca. 20% less than that when the reaction solutions are purged with argon. In the case
of [Ru(bpy)2Cl2]+ the rate constant equals 1.8×105 M–1 s–1 under similar conditions in air, showing higher reactivity of Ru complexes compared with Os ones. The reduction is pH-dependent
with a maximum around 7. Added for solubilization of poorly soluble metal complexes, surfactants decrease the rates of the
enzymatic reaction. The retardation effect increases in the series: cetyltrimethylammonium bromide < Triton X-100 < sodium
dodecyl sulfate, i.e. on going from positively charged to neutral and then to negatively charged surfactants. The behavior
of the OsIII and RuIII complexes toward reduced glucose oxidase contrasts to that of recently studied ferricenium cations. As opposed to the latter,
the former do not show kinetically meaningful binding with the enzyme, and the Michaelis kinetics typical of the ferricenium
case is not realized for the OsIII, and RuIII species. The systems OsIII- or RuIII-glucose oxidase are convenient for routine "one pot" spectrophotometric monitoring of the d-glucose content in samples, since the metal reduction to MII is accompanied by a strong increase in absorbance in the visible spectral region.
Received: 1 July 1998 / Accepted: 13 January 1999 相似文献
32.
N. V. Belova N. G. Emel’yanova A. P. Makeeva I. N. Ryabov 《Journal of Ichthyology》2007,47(5):366-384
The state of the reproductive system in several fish species—offspring of individuals exposed to radiation as a result of the catastrophe at the Chernobyl Nuclear Power Plant (CNPP) was studied. Material was collected in water bodies of Ukraine polluted with radionuclides: water cooler of the CNPP (1992, 2002–2004), Lake Glubokoe (2003–2004), Kiev Reservoir, and Teterev River (1997, 1999–2005). It was shown that the total number and the degree of disturbances in gonads of the studied fish species were positively correlated with the levels of pollution of water bodies: in the cleanest water body, Teterev River, the proportion of fish with gonads without considerable deviations was about 78%; in the Kiev Reservoir, 67%; in the water cooler, 51%; and in Lake Glubokoe, 45%. By the number and pattern of gonad anomalies, species specificity in their response to the radiation background was revealed. A smaller degree of damage of sexual cells and gonads in unisexual (triploid) populations of goldfish Carassius auratus reproducing gynogenetically, as compared to bisexual (diploid) populations, was detected. Among postemergency generations of the studied fish species, in all water bodies the number and degree of gonad disturbances were in F2–4, in Kiev Reservoir and Teterev River, this was most likely accounted for by the phenomenon of prolonged mutagenesis. 相似文献
33.
Vertical distribution and composition of phytoplankton under the influence of an upper mixed layer 总被引:5,自引:0,他引:5
The vertical distribution of phytoplankton is of fundamental importance for the dynamics and structure of aquatic communities. Here, using an advection-reaction-diffusion model, we investigate the distribution and competition of phytoplankton species in a water column, in which inverse resource gradients of light and a nutrient can limit growth of the biomass. This problem poses a challenge for ecologists, as the location of a production layer is not fixed, but rather depends on many internal parameters and environmental factors. In particular, we study the influence of an upper mixed layer (UML) in this system and show that it leads to a variety of dynamic effects: (i) Our model predicts alternative density profiles with a maximum of biomass either within or below the UML, thereby the system may be bistable or the relaxation from an unstable state may require a long-lasting transition. (ii) Reduced mixing in the deep layer can induce oscillations of the biomass; we show that a UML can sustain these oscillations even if the diffusivity is less than the critical mixing for a sinking phytoplankton population. (iii) A UML can strongly modify the outcome of competition between different phytoplankton species, yielding bistability both in the spatial distribution and in the species composition. (iv) A light limited species can obtain a competitive advantage if the diffusivity in the deep layers is reduced below a critical value. This yields a subtle competitive exclusion effect, where the oscillatory states in the deep layers are displaced by steady solutions in the UML. Finally, we present a novel graphical approach for deducing the competition outcome and for the analysis of the role of a UML in aquatic systems. 相似文献
34.
Cell-to-Cell, but not long-distance, spread of RNA silencing that is induced in individual epidermal cells 总被引:4,自引:0,他引:4
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A Turnip crinkle virus (TCV)-based system was devised to discriminate cell-to-cell and systemic long-distance spread of RNA silencing in plants. Modified TCV-GFPDeltaCP, constructed by replacing the coat protein (CP) gene with the green fluorescent protein (GFP) gene, replicated in single epidermal cells but failed to move from cell to cell in Nicotiana benthamiana. Mechanical inoculation of TCV-GFPDeltaCP induced effective RNA silencing in single epidermal cells which spread from cell to cell to form silenced foci on inoculated leaves, but no long-distance systemic spread of RNA silencing occurred. Agroinfiltration of TCV-GFPDeltaCP was, however, able to induce both local and systemic RNA silencing. TCV coinfection arrested TCV-GFPDeltaCP-mediated local induction of RNA silencing. Possible mechanisms involved in cell-to-cell and long-distance spread of RNA silencing are discussed. 相似文献
35.
N. V. Belova N. G. Emel’yanova A. P. Makeeva I. N. Ryabov 《Journal of Ichthyology》2006,46(9):779-787
The state of the reproductive system of Tinca tinca—descendants of individuals that were exposed to radiation as a result of the catastrophe at the Chernobyl Nuclear Power Plant in 1986 was studied. Material was collected in the postemergency period in radionuclide-polluted water bodies: in the Ukraine, in Kiev Reservoir, the Teterev River, and Lake Glubokoe (1999–2005) and in Belarus, in Lake Svyatoe (1998–1999). It is demonstrated that the total number and the extent of disturbances in the gonads of T. tinca are positively related to the levels of pollution in water bodies: in the cleanest water body, the Teterev River, the proportion of fish with gonads without considerable deviations was about 93%; in Kiev Reservoir, 79%, and in Lake Svyatoe, only 18%. Among the “postemergency” generations of T. tinca, the maximum number of disturbances in sexual cells and gonads was recorded in F3–4, which is evidently caused by a phenomenon of the “prolonged mutagenesis”. A relatively high species resistance of the reproductive system of T. tinca to the radiation impact, in comparison with other cyprinids, was recorded. 相似文献
36.
The characteristics of absolute auditory sensitivity of the bottlenose dolphin (Tursiops truncatus) in the transverse plane have been measured using short broadband stimuli simulating dolphin clicks (with energy maximum
at frequencies 8, 16, 30, 50 and 100 kHz). Experiments were performed using the method of conditioned reflexes with food reinforcement.
It is shown that, in the frequency range of 8–30 kHz, the absolute sensitivity of dolphin hearing in any ventral and lateral
directions of the transverse plane is only 2–8 dB worse than in the rostral direction. Moreover, it is 25–30 dB better than
at 50–100 kHz. At 8–30 kHz, pronounced dorsoventral asymmetry has been observed. In this frequency range, it reaches 15–18
dB whereas at 50–100 kHz this asymmetry decreases to 2–3 dB. In the dorsal direction, the auditory sensitivity is 18 dB worse
than in the rostral one at ∼8 kHz, and the difference rises smoothly to 33 dB at ∼100 kHz. At 50–100 kHz, the acoustical thresholds
in the transverse plane relative to those for the with rostral direction get worse almost uniformly in all directions by 25–33
dB. As a result, in the transverse plane the beam patterns are nearly circular, unlike those at 8–30 kHz. The results are
discussed in terms of the model of sound perception through the left and right mental foramens. The biological relevance of
such asymmetry is emphasized. 相似文献
37.
Resource competition is a fundamental interaction in natural communities. However, little remains known about competition in spatial environments where organisms are able to regulate resource distributions. Here, we analyse the competition of two consumers for two resources in a one-dimensional habitat in which the resources are supplied from opposite sides. We show that the success of an invading species crucially depends on the slope of the resource gradients shaped by the resident. Our analysis reveals that parameter combinations, which lead to coexistence in a uniform environment, may favour alternative stable states in a spatial system, and vice versa. Furthermore, differences in growth rate, mortality or dispersal abilities allow a consumer to coexist stationarily with - or even outcompete - a competitor with lower resource requirements. Applying our theory to a phytoplankton model, we explain shifts in the community structure that are induced by environmental changes. 相似文献
38.
Imperfect prey selectivity of predators promotes biodiversity and irregularity in food webs
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Ecological communities are often characterised by many species occupying the same trophic level and competing over a small number of vital resources. The mechanisms maintaining high biodiversity in such systems are still poorly understood. Here, we revisit the role of prey selectivity by generalist predators in promoting biodiversity. We consider a generic tri‐trophic food web, consisting of a single limiting resource, a large number of primary producers and a generalist predator. We suggest a framework to describe the predator functional response, combining food selectivity for distinctly different functional prey groups with proportion‐based consumption of similar prey species. Our simulations reveal that intermediate levels of prey selectivity can explain a high species richness, functional biodiversity, and variability among prey species. In contrast, perfect food selectivity or purely proportion‐based food consumption leads to a collapse of prey functional biodiversity. Our results are in agreement with empirical phytoplankton rank‐abundance curves in lakes. 相似文献
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Ana M Perez O’Brien Daniela H?ller Solomon A Boison Marco Milanesi Lorenzo Bomba Yuri T Utsunomiya Roberto Carvalheiro Haroldo HR Neves Marcos VB da Silva Curtis P VanTassell Tad S Sonstegard Gábor Mészáros Paolo Ajmone-Marsan Fernando Garcia Johann S?lkner 《遗传、选种与进化》2015,47(1)