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1.
Current theories of stable circadian entrainment postulate phase delays should be associated with period lengthening, while phase advances should be associated with period shortening. While characterising features of the rat PRC to light, we noted substantial numbers of responses that displayed the opposite pattern. Forty-eight rats provided data for 192 phase responses. Limiting our analysis to phase shifts greater than 1 hour, we found 44 displayed the expected predicted relationship, and 33 displayed the contrary paradoxical relationship. Paradoxical responders possessed significantly shorter initial activity periods, compared to predicted responders. Activity was significantly lengthened by paradoxical responders and shortened by predicted responders following light pulse exposure. These results suggest a second mode of stable entrainment. Additionally, these results indicate entrainment mode, predicted or paradoxical, is based upon activity period duration. Short activity period durations will be associated with paradoxical responses, long durations will be associated with predicted responses. We argue that, given the dynamic changes in photoperiod, both modes of entrainment are necessary to provide stable entrainment across the year. 相似文献
2.
Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications 总被引:1,自引:0,他引:1
Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of
individuals representing 54 species of frogs, two species of salamanders, a
caecilian, and a lungfish. Eight of these sites were present in all species
examined, and two were found in all but one species. Alignment of these
conserved restriction sites revealed, among anuran 28S rRNA genes, five
regions of major length variation that correspond to four of 12 previously
identified divergent domains of this gene. One of the divergent domains
(DD8) consists of two regions of length variation separated by a short
segment that is conserved at least throughout tetrapods. Most of the
insertions, deletions, and restriction-site variations identified in the
28S gene will require sequence-level analysis for a detailed reconstruction
of their history. However, an insertion in DD9 that is coextensive with
frogs in the suborder Neobatrachia, a BstEII site that is limited to
representatives of two leptodactylid subfamilies, and a deletion in DD10
that is found only in three ranoid genera are probably synapomorphies.
相似文献
3.
A spectrophotometric assay for 6-phosphogluconolactonase involving the use of immobilized enzymes to prepare the labile 6-phosphoglucono-delta-lactone substrate.
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We report the development of a new spectrophotometric assay for 6-phosphogluconolactonase. The labile substrate 6-phosphoglucono-delta-lactone is prepared from glucose 6-phosphate by enzymes co-immobilized on Sepharose beads. The assay has the advantages of high sensitivity for routine determination of enzyme activity and allows determination of both Km and Vmax. from a single assay. A method for estimating the contribution of spontaneous hydrolysis to total hydrolysis is described. This assay overcomes the problems encountered with all previous assays. 相似文献
4.
Myocyte deenergization and intracellular free calcium dynamics 总被引:1,自引:0,他引:1
5.
Direct measurement of the poliovirus RNA polymerase error frequency in vitro. 总被引:15,自引:12,他引:3
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The fidelity of RNA replication by the poliovirus-RNA-dependent RNA polymerase was examined by copying homopolymeric RNA templates in vitro. The poliovirus RNA polymerase was extensively purified and used to copy poly(A), poly(C), or poly(I) templates with equimolar concentrations of noncomplementary and complementary ribonucleotides. The error frequency was expressed as the amount of a noncomplementary nucleotide incorporated divided by the total amount of complementary and noncomplementary nucleotide incorporated. The polymerase error frequencies were very high and ranged from 7 x 10(-4) to 5.4 x 10(-3), depending on the specific reaction conditions. There were no significant differences among the error frequencies obtained with different noncomplementary nucleotide substrates on a given template or between the values determined on two different templates for a specific noncomplementary substrate. The activity of the polymerase on poly(U) and poly(G) was too low to measure error frequencies on these templates. A fivefold increase in the error frequency was observed when the reaction conditions were changed from 3.0 mM Mg2+ (pH 7.0) to 7.0 mM Mg2+ (pH 8.0). This increase in the error frequency correlates with an eightfold increase in the elongation rate that was observed under the same conditions in a previous study. 相似文献
6.
Cryptosporidiosis in ferrets 总被引:3,自引:0,他引:3
The diagnosis of cryptosporidiosis in two ferrets who died from unrelated causes prompted a survey to determine the prevalence and incidence of the infection in ferrets at our facility. The survey of the existing ferret population and all new arrivals indicated cryptosporidiosis occurred as a subclinical disease in a high percentage of young ferrets: 40% of the ferret population and 38 to 100% of the new arrivals had cryptosporidial oocysts in their feces. The infection was found to persist for several weeks in both immunocompetent and immunosuppressed ferrets. The interspecies transmission of Cryptosporidium implies that infected ferrets should be considered a potential source of infection for the general population. 相似文献
7.
Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells 总被引:4,自引:2,他引:2
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Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction. 相似文献
8.
Darryl J. Lee Maria J. Stokes Robert J. Taylor Robert G. Cooper 《European journal of applied physiology and occupational physiology》1992,64(3):199-203
In 31 normal subjects (17 male), aged 19-48 years, and 8 patients with chronic low back pain (4 male), aged 37-55 years, the repeatability of surface recordings of acoustic myography (AMG) and electromyography (EMG) were examined in the lumbar paraspinal muscles. Five isometric test positions were examined. In 21 of the normal subjects, four positions tested were: quiet standing, half extension from prone lying, full extension from prone with and without resistance. In 10 of the normal subjects and the 8 back pain patients, a standardised, unsupported horizontal position with the upper body over the end of a couch was tested. The AMG and EMG signals were full-wave rectified and integrated (iAMG and iEMG). The variability of recordings during repeated 5-s isometric contractions was assessed by analysis of variance (ANOVA) and the coefficient of variation (CV) was calculated from the ANOVA. Both recording techniques produced the most repeatable results during the unsupported, horizontal hold position. In the normal subjects, CV were, iAMG 5.6%, iEMG 4.9%; and in the patients, iAMG 4.4%, iEMG 2.6%. The CV for the other four isometric test positions ranged from 15.3% to 29.4% for iAMG, and 8% to 15.7% for iEMG. These results demonstrated that a controlled test manoeuvre for examining AMG and EMG of the paraspinal muscles was vital for repeatable recordings. The CV for the standardised, horizontal position were lower than for previously published results.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
9.
We have sequenced the ebgA (evolved beta-galactosidase) gene of Escherichia
coli K12. The sequence shows 50% nucleotide identity with the E. coli lacZ
gene, demonstrating that the two genes are related by descent from a common
ancestral gene. Comparison of the two sequences suggests that the ebgA gene
has recently been under selection. A significant excess of identical,
rather than synonymous, codons used to encode identical amino acids at the
same positions in the aligned sequences implies that some form of selection
is operating directly at the DNA level. This selection is independent of,
and in addition to, selection based on codon usage or on function of the
gene products.
相似文献
10.
Gerald V. Stokes 《Journal of bacteriology》1974,118(2):616-620
L cells (mouse fibroblasts) infected with Chlamydia psittaci (strain meningopneumonitis) produced a proteinase differing in solubility in ammonium sulfate from the proteinase of uninfected L cells. Synthesis of the enzyme was inhibited by chloramphenicol but not by cycloheximide, indicating that the new proteinase in infected L cells was synthesized by Chlamydia psittaci. The chlamydial proteinase had no demonstrable ion requirements and was not inhibited by a variety of inhibitors of proteinase activity. Gel filtration experiments suggested a molecular weight of approximately 250,000. The proteinase appeared in infected L cells at the time host cells began to die and the large chlamydial cells began to reorganize into small ones. Some possible functions for the chlamydial proteinase were proposed. 相似文献