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41.
Flavio Massimo Garlaschi Giuseppe Zucchelli Robert Charles Jennings 《Photosynthesis research》1989,20(3):207-220
An experimental analysis is presented concerning the effect on relative light absorption by the two photosystems caused by (a) a highly light scattering environment (the detour effect) and (b) light filtration across successive chloroplast layers (the light attenuation effect). Both suspensions of isolated chloroplasts and leaves were employed.It is concluded that within a single spinach leaf these phenomena are likely to lead to only rather small increases in relative photosystem I absorption and activity with respect to photosystem II and will thus not exert a significant effect on non cyclic electron transport. On the contrary when light is filtrated across successive vegetation layers (shade light) significant increases in the relative PSI absorption and activity may be encountered.It is determined that the detour effect in mature leaves from a variety of plants increases overall photosynthetically useful light absorption by 35–40%.Abbreviations FM
maximal fluorescence
- LHCP2
light-harvesting chlorophyl a/b protein complex II
- QA-primary
quinone acceptor of photosystem II 相似文献
42.
Effect of orally-administered epidermal growth factor on intestinal iron absorption and mucosal permeability 总被引:1,自引:0,他引:1
A progressive increase in intestinal 59Fe3+ absorption was observed on oral feeding of mice with physiological doses of EGF/UGO. Maximal changes were apparent after 3d and appeared to be dose-dependent. In addition to a small increase in intestinal cell proliferation, as reflected by increased ornithine decarboxylase activity, EGF/UGO-feeding increased mucosal permeability (evaluated with [51Cr]-EDTA): the latter could account for the increase in iron absorption. Sialoadenectomy, to remove the major source of endogenous EGF/UGO, had no appreciable effect on the intestinal absorption of iron. 相似文献
43.
We present a simple model describing the transition between the prefiring, firing and postfiring phases of a single neuron in a large neural net. Using typical values for the physiological parameters that enter the model, we find average interspike times that are close to those reported in experimental measurements. 相似文献
44.
45.
This minireview makes an initial assessment of the progress made using anisotropy decay measurements for investigating the conformational changes and molecular dynamics in soluble systems. A critical analysis of available data is presented. The anisotropy decays of the tryptophan fluorescence of staphylococcal nuclease, adrenocorticotropin, melittin and of labeled transfer RNA were studied for investigating the functional conformational changes of these systems. The emissions of variously labeled immunoglobulins have been used to elucidate the conformations of these proteins before and after the binding of specific antibodies. Labeled myosin and its fragments have given information on the functional motions of the protein domains. The anisotropy decays of labeled and natural hemoglobin systems have been utilized for exploring the allosteric behavior of these molecules. The data suggest a wide applicability of this technique to the study of protein dynamics and conformational changes of macromolecules. 相似文献
46.
Application of general tracer theory to the problem of estimating fluxes of tracee between the gastrointestinal tract and
the body proper, from observations of the movement of tracer, shows that a number of assumptions must be fulfilled. Two specific
sets of assumptions are discussed and, in both cases, measurement of tracer fluxes yields information on the integrated absorption
of the tracee. 相似文献
47.
Judith R. Turnlund Leslie Wada Janet C. King William R. Keyes Lorra L. Acord 《Biological trace element research》1988,17(1):31-41
Copper absorption was measured at two levels of dietary zinc in six healthy young men who were confined to a metabolic unit
for a 75 d study of zinc utilization. A diet of conventional foods was fed, providing either 16.5 or 5.5 mg zinc and 1.3 mg
copper daily. Copper absorption was determined by feeding65Cu, a stable isotope of copper, once during the 16.5 mg Zn diet and near the beginning and end of the 5.5 mg Zn diet. Apparent
copper absorption averaged 48.1% when the 16.5 mg Zn diet was fed. This was significantly higher than the averages of 37.2
and 38.5% when the 5.5 mg Zn diet was fed. Absorption also differed significantly among subjects. Fecal copper did not differ
between diets or among subjects. All subjects were in positive copper balance at both levels of dietary zinc. These results
suggest that a dietary zinc intake slightly above the Recommended Dietary Allowance of 15 mg/d does not increase fecal copper
loss and does not interfere with copper absorption. 相似文献
48.
The fluorescence behavior of adenosine in neutral solution has been studied by time-resolved spectroscopy using synchrotron excitation and timecorrelated single photon counting, and by decay time measurements. Three emissions have been identified and correlated with three excitation spectra. The assignment of these transitions has been made by comparison with similar measurements on 6N, 6N-dimethyladenosine (6 DMA), and on adenosine in acid solution (ADO H+). It is proposed that two of the transitions of adenosine which correlate with 6DMA originate from coplanar and orthogonal rotational conformers of the amino group. The other transition, correlating with ADO H+ may originate either from the 3H-imino tautomer, or from a differently solvated rotational conformer.A partial presentation of this work has been made at the Second Congress of the European Society for Photobiology Padova, Italy, 6–10 September 1987 相似文献
49.
UV-visible and 13C NMR measurements described in the literature and our 31P NMR measurements support the following mechanism of proton transfer reactions in aqueous solutions of pyridoxamine phosphate: Only the tautomeric equilibrium between neutral form, A
N, and zwitterion, A
Z, which is analogous to the tautomeric equilibrium of 3-hydroxypyridine in aqueous solution, is important, and that equilibrium does not change upon the dissociation of the second phosphate proton. With these simplifying assumption, we have simulated the relaxation spectrum of the proton transfer reactions of pyridoxamine phosphate in water using parameters from analogous reactions and compared it with our ultrasound and temperature jump measurements. We have found that the relaxation process measured by the temperature jump experiment is mainly caused by the overall reaction A
N=A
Z (or A
N
-
=A
Z
-
) and the ultrasound absorption at the isoelectric point between pK2 and pK3 is mainly caused by the overall reaction
. 相似文献
50.
The intrinsic rates of increase of insects of different sizes 总被引:2,自引:0,他引:2
K. J. GASTON 《Ecological Entomology》1988,13(4):399-409
ABSTRACT.
- 1 A negative relationship between intrinsic rate of increase, r, and body size has only clearly been shown using data for species drawn from a number of phyla and covering several orders of magnitude in size. Analyses for more closely related species are equivocal.
- 2 Data for ninety-one species of insects, from nine orders, were used to examine the correlation between intrinsic rate of increase and size.
- 3 Intrinsic rate of increase was negatively correlated with both length and weight across orders, but no relationship could be shown within orders.
- 4 Generation times were positively related to body size, but there was no relationship between net reproductive rate (RQ) and size.
- 5 These results support the hypothesis that documented relationships between species size and colonization success in insects could be a consequence of the scaling of intrinsic rate of increase with size.