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71.
Feedback lighting provides illumination primarily during the subjective night (i.e., the photosensitive portion of the circadian cycle) in response to a given behavior. This technique has previously been used to test the nonparametric model of entrainment in nocturnal rodents. In three species (Rattus norvegicus, Mesocricetus auratus, and Mus musculus), the free-running period of the locomotor activity rhythm was similar whether the animals were exposed to continuous light or discrete light pulses occurring essentially only during the subjective night (i.e., feedback lighting). In the current experiments, feedback lighting was presented to squirrel monkeys so that light fell predominantly during the subjective night. Feedback lighting was linked to the drinking behavior in this diurnal primate so that when the animal drank, the lights went out. Despite the seemingly adverse predicament, the monkeys maintained regular circadian drinking rhythms. Furthermore, just as the period of the free-running activity rhythms of nocturnal rodents exposed to continuous light or feedback lighting were similar, the period of the drinking rhythms of the squirrel monkeys in continuous light and feedback lighting were comparable (25.6 +/- 0.1 and 25.9 +/- 0.1 hours, respectively), despite a substantial decrease in the total amount of light exposure associated with feedback lighting. The free-running period of monkeys exposed to continuous dark (24.5 +/- 0.1 hours) was significantly shorter than either of the two lighting conditions (P < 0.001). The results presented for the drinking rhythm were confirmed by examination of the temperature and activity rhythms. Therefore, discrete light pulses given predominately during the subjective night are capable of simulating the effects of continuous light on the free-running period of the circadian rhythms of a diurnal primate. The response of squirrel monkeys to feedback lighting thus lends further support for the model and suggests that the major entrainment mechanisms are similar in nocturnal rodents and diurnal primates. 相似文献
72.
Pseudomonas fluorescens biovar I was isolated from a pulp mill effluent based on its ability to grow on synthetic media containing 1,2-diarylethane structures as the sole carbon and energy source. Analysis of samples taken from cultures of this strain in benzoin or 4,4-dimethoxybenzoin (anisoin), showed that cleavage between the two aliphatic carbons takes place prior to ring fission. Intermonomeric cleavage was also obtained with crude extracts. Substrates of this reaction were only those 1,2-diarylethane compounds that supported growth of the bacterium. The purification and partial characterization of an enzyme that catalyzes the NADH-dependent reduction of the carbonyl group of benzoin and anisoin is also reported. 相似文献
73.
Cannibalism as a life boat mechanism 总被引:2,自引:0,他引:2
Under certain conditions a cannibalistic population can survive when food for the adults is too scarce to support a non-cannibalistic population. Cannibalism can have this lifeboat effect if (i) the juveniles feed on a resource inaccessible to the adults; and (ii) the adults are cannibalistic and thus incorporate indirectly the inaccessible resource. Using a simple model we conclude that the mechanism works when, at low population densities, the average yield, in terms of new offspring, due to the energy provided by one cannibalized juvenile is larger than one. 相似文献
74.
P. M. Abuja M. Schmuck I. Pilz P. Tomme M. Claeyssens H. Esterbauer 《European biophysics journal : EBJ》1988,15(6):339-342
Limited proteolysis (papain) of the cellobiohydrolase I (CBH I, 65 kDa) from Trichoderma reesei led to the seperation of two functional domains: a core protein (55 kDa) containing the active site, and a C-terminal glycopeptide (10 kDa) implicated in binding to the insoluble matrix (cellulose). The quaternary structures of the intact CBH I and its core in solution are now compared by small angle X-ray scattering (SAXS) measurements. The molecular parameters derived for the core (Rg=2.09 nm, Dmax=6.5 nm) and for the intact enzyme (Rg=4.27 nm, Dmax=18 nm) indicate very different shapes. The resulting models show a tadpole-like structure for the intact enzyme where the isotropic part coincides with the core protein and the flexible tail part should be identified with the C-terminal glycopeptide. Thus in this enzyme, functional differentiation is reflected in structural peculiarities.Abbreviations SAXS
small angle X-ray scattering
- SDS-PAGE
SDS-polyacrylamide gel electrophoresis
- IEF-PAG
polyacrylamide gel isoelectric focusing; cellobiohydrolase (CBH, 1,4--glucan cellobio hydrolase (E.C.3.2.1.91))
- Dmax
maximum diameter
- Rg
radius of gyration 相似文献
75.
A model is proposed for the effect of gramicidin A on the order and structure of phospholipid dispersions. According to this model, the addition of gramicidin A influences the surrounding lipids via two independent mechanisms. The first arises from a drop in surface pressure for those lipids substantially bounded by gramicidin A. The second mechanism arises from the increase in the phospholipid headgroup spacing due to the small polar region of the polypeptide. The model provides an explanation for the currently available NMR, X-ray diffraction and Langmuir monolayer results. The model also suggests mechanisms for the ability of gramicidin A to trigger a transition of the lipid from the lamellar to hexagonal II phase, the dependence of this transition on the lipid chain length and the formation of a lamellar phase with lysophosphatidylcholine.Abbreviations NMR
nuclear magnetic resonance
- DMPC
dimyristoylphosphatidylcholine
- S
molecular order parameter
- CSA
chemical shift anisotropy
- DPPC
dipalmitoylphosphati-dylcholine
- LPC
lysophosphatidylcholine 相似文献
76.
77.
C K Chou 《Bioelectromagnetics》1992,13(6):581-597
Hyperthermia has been used in conjunction with radiation and chemotherapy for cancer treatment. When using electromagnetic heating, applicators are critical components in contact with or in proximity to patients and can be the determining factor for effective and safe treatment. Tissue absorption of electromagnetic energy is determined by many factors. Three cases are shown to illustrate the complexity of microwave heating: 1) The BSD MA-151 applicator has good center heating on a muscle-only phantom as shown in the operation manual. When fat slabs of 0.25, 0.5, 1, and 2 cm thick were added, two hot spots near the periphery of the applicator were evident on all fat surfaces, exposed at 631 MHz. At 915 MHz, the heating was elongated on the surface of the models with 0.25- and 2-cm fat, and two hot spots were observed on the 0.5- and 1-cm fat surfaces. 2) Heating patterns of the Clini-Therm applicators on a muscle-only phantom, as indicated in the operations guide, are elliptical with their major axes perpendicular to the electric field. However, when a bolus is used, the elliptical pattern is parallel to the E field. 3) Heating patterns in cylindrical structures were studied with inhomogeneous models of limbs. Arm and thigh models consisting of fat, bone, and muscle material were heated with Clini-Therm L, M, and MS applicators at 915 MHz. In addition to the geometric effect, the results indicated that placing the applicators with E field parallel to the long axis of cylindrical structures can minimize required power, produce less heating of fats and reduce stray radiation. In conclusion, to apply penetrating microwave or other RF fields for tissue heating, one must simulate the clinical exposure conditions as closely as possible to obtain useful heating patterns. 相似文献
78.
John J. Marchalonis Fatma Dedeoglu Hulya Kaymaz Samuel F. Schluter Allen B. Edmundson 《Journal of Protein Chemistry》1992,11(2):129-137
Although the amino acid sequence and three-dimensional structure of human immunoglobulin light chains have been known for more than 15 years, the location of antigenic markers characteristic of chains has not been determined. Here, we use a set of synthetic overlapping peptides to completely model the sequence of the chain Mcg and test these for the binding or rabbit and goat antisera specific for chain determinants. We assess peptide contributions to -antigenic reactivity and also to identify a portion of C-region where conformational factors contribute to the antigenicity. Specific determinants occur both in the constant and variable (first and third framework) domains of the molecule. The fourth framework of the variable region, a segment specified by the joining gene, is also recognized and cross-reacts antigenically with the homologous region of T cell receptor chains. Major specific determinants are localized in the N- and C-terminal segments, which are linear and devoid of major conformational folding. Other segments that are strongly antigenic, such as the third framework of the V region (residue 78–93) and a segment of the constant region (residues 177–192), show strong conformational dependence in antigenicity. 相似文献
79.
Michael J. Jenkins James Sneyd Scott Camazine J. D. Murray 《Journal of mathematical biology》1992,30(3):281-306
We present a simplified version of a previously presented model (Camazine et al. (1990)) that generates the characteristic
pattern of honey, pollen and brood which develops on combs in honey bee colonies. We demonstrate that the formation of a band
of pollen surrounding the brood area is dependent on the assumed form of the honey and pollen removal terms, and that a significant
pollen band arises as the parameter controlling the rate of pollen input passes through a bifurcation value. The persistence
of the pollen band after a temporary increase in pollen input can be predicted from the model. We also determine conditions
on the parameters which ensure the accumulation of honey in the periphery and demonstrate that, although there is an important
qualitative difference between the simplified and complete models, an analysis of the simplified version helps us understand
many biological aspects of the more complex complete model.
Corresponding author 相似文献
80.
Coen van den Berg Ferdinand A. Sibbing Jan W. M. Osse Wim Hoogenboezem 《Environmental Biology of Fishes》1992,33(1-2):105-124
Synopsis The filter feeding organ of cyprinid fishes is the branchial sieve, which consists of a mesh formed by gill rakers and tiny channels on the gill arches. In order to establish its possible role during growth we measured the following morphological gill raker parameters over a range of sizes in three cyprinid fishes, bream, white bream and roach: inter raker distance, bony raker length, raker width, cushion length and channel width. At any given standard length common bream has the largest inter raker distance, roach the lowest and white bream is intermediate. In the comb model of filter feeding the inter raker distance is considered to be a direct measure of the mesh size and retention ability (= minimal size of prey that can be retained) of a filter. For the three species under study there is a conflict between the comb model and experimental data on particle retention. Lammens et al. (1987) found that common bream has a large retention ability whereas roach and white bream have a much smaller one. A new model, the channel model (Hoogenboezem et al. 1991) has been developed for common bream; in this model the lateral gill rakers can regulate the mesh size of the medial channels on the other side of the gill slit. The present data indicate that this model is not appropriate for white bream and roach. At any given standard length white bream and roach only reach 70% of the raker length of common bream, which means that in this model the gill slits should to be very narrow during filter feeding. The gill rakers consist of a bony raker and a fleshy cushion. The bony rakers have a rather long needle-like part outside the cushion in bream, but not in white bream and roach which have blunt gill rakers. Blunt gill rakers are not suited to reduce the diameter of the medial channels. The comb model seems more appropriate for white bream and roach, but doubts about the validity of this simple model remain. The sum of the areas of the medial channels is an approximation of the area through which water flows in the filter. This channel area therefore gives an impression of the capacity or flow rate of the filter. With this capacity estimation and an estimation of energy consumption we calculated an energy ratio of filter feeding. The energy ratio decreases with increasing standard length with an exponent close to the expected exponent of -0.40. The energy ratio is highest in bream, intermediate in white bream and lowest in roach. 相似文献