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1.
2.
Summary A formalin—calcium fixation method of preparing cryosections is described, which allows demonstration of Langerhans' cells by S100 antigen staining on frozen sections. The number of Langerhans' cells given by T6 antigen staining is also higher in formalin—calcium fixed frozen sections than acetone fixed frozen sections. The preparation is suitable for dual demonstration of the two antigens on the same section enabling a more accurate numerical evaluation of Langerhans' cell populations in the normal cervical epithelium. 相似文献
3.
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
4.
The standard Nb2 assay for biologically active prolactin has been modified to allow a rapid convenient microbioassay without loss of specificity or accuracy. Lactogenic hormones specifically stimulate the replication of Nb2 node rat lymphoma cells in suspension culture and form the basis of a currently available bioassay to measure prolactin and growth hormone in human serum. A new microbioassay was developed using microtest plates enabling a large number of samples to be assayed simultaneously whilst maintaining the overall sensitivity of the bioassay for lactogenic hormones. Growth of the Nb2 node lymphoma cells, measured by a light scattering technique using optical density on a spectrophotometer, was shown to be closely correlated with the cell number determined on a Coulter counter. Addition of excess anti-human prolactin and anti-human growth hormone completely inhibited the growth stimulatory effects of both human prolactin and human growth hormone. This new microbioassay (BA) and conventional radioimmunoassay (RIA) were used to measure lactogenic hormones in 48 normal subjects. There was a close correlation between the results of both assays for each hormone studied in the control sera. The mean basal BA/RIA ratio was 1.5 (range 0.8-2.0) for prolactin, 0.7 (range 0-4.5) for growth hormone and 1.3 (range 0.5-1.9) for total lactogenic activity. 相似文献
5.
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
6.
Summary The production of solvents from whey permeate in batch fermentation usingClostridium
acetobutylicum P262 was examined. An overall reactor productivity of 0.24 g/l.h was observed, representing a marked improvement over reports using other strains of clostridia. Using a semi-synthetic medium galactose was shown to be as effective a substrate as glucose. When whey permeate was used in which the lactose was hydrolysed prior to fermentation, preferential uptake of glucose over galactose was observed, and such hydrolysis provided no advantage to the fermentation process. 相似文献
7.
I. S. Maddox K. Spencer J. M. Greenwood M. W. Dawson J. D. Brooks 《Biotechnology letters》1985,7(11):815-818
Summary One strain each of the fungus,Aspergillus
niger, and the yeast,Saccharomycopsis
lipolytica, were investigated for their ability to produce citric acid from the sugars present in hemicellulose hydrolysates.S.
lipolytica produced citric acid as efficiently from mannose as from glucose, but failed to assimilate xylose, arabinose or galactose.A.
niger readily assimilated mannose, xylose and arabinose, and produced citric acid from these sugars although the yields were lower than from glucose. A possible inhibitory effect of arabinose on citric acid production from other sugars was observed usingA.
niger. 相似文献
8.
Summary The effect of methanol on the ability of several strains of Aspergillus to produce citric acid from galactose has been investigated. In the absence of methanol, very little production (less than 1 g/l) was observed. In the presence of methanol (final concentration 1% v/v), however, citric acid production and yeilds were increased considerably. Strong relationships were observed between citric acid production and the activities of the enzymes 2-oxoglutarate dehydrogenase and pyruvate carboxylase in cell-free extracts. During citric acid production, in the presence of methanol, the activity of 2-oxoglutarate dehydrogenase was low and that of pyruvate carboxylase high. In the absence of methanol, where little citric acid was produced, the reverse was true. It is suggested that the presence of methanol may increase the permeability of the cell to citrate, and the cell responds to the diminished intracellular level by increasing production via repression of 2-oxoglutarate dehydrogenase. 相似文献
9.
Colloquium on scientific authorship: rights and responsibilities 总被引:1,自引:0,他引:1
A N Schechter J B Wyngaarden J T Edsall J Maddox A S Relman M Angell W W Stewart 《FASEB journal》1989,3(2):209-217
The Colloquium on Scientific Authorship was held at the National Institutes of Health (NIH) at a time of extraordinary scrutiny by the public of the ethics of scientists, as represented by intense interest of the press and the Congress of the United States. Indeed, several regulations dealing with scientific misconduct have been proposed during the last year in the Federal Register, and new legislation has been proposed in the Congress. As a result of these concerns, conferences have been organized by the Institute of Medicine, the American Association for the Advancement of Science/American Bar Association, the Council of Biology Editors, and other groups. The colloquium at NIH, which was held May 31, 1988, and sponsored by the Intramural Scientists, focused on publication practices, especially multiple authorship, as contributing to perceived difficulties. The participants suggested various changes in conventions related to authorship that might help prevent future problems. 相似文献
10.
Excess amino acid polymorphism in mitochondrial DNA: contrasts among genes from Drosophila, mice, and humans 总被引:13,自引:3,他引:10
Recent studies of mitochondrial DNA (mtDNA) variation in mammals and
Drosophila have shown an excess of amino acid variation within species
(replacement polymorphism) relative to the number of silent and replacement
differences fixed between species. To examine further this pattern of
nonneutral mtDNA evolution, we present sequence data for the ND3 and ND5
genes from 59 lines of Drosophila melanogaster and 29 lines of D. simulans.
Of interest are the frequency spectra of silent and replacement
polymorphisms, and potential variation among genes and taxa in the
departures from neutral expectations. The Drosophila ND3 and ND5 data show
no significant excess of replacement polymorphism using the
McDonald-Kreitman test. These data are in contrast to significant
departures from neutrality for the ND3 gene in mammals and other genes in
Drosophila mtDNA (cytochrome b and ATPase 6). Pooled across genes, however,
both Drosophila and human mtDNA show very significant excesses of amino
acid polymorphism. Silent polymorphisms at ND5 show a significantly higher
variance in frequency than replacement polymorphisms, and the latter show a
significant skew toward low frequencies (Tajima's D = -1.954). These
patterns are interpreted in light of the nearly neutral theory where mildly
deleterious amino acid haplotypes are observed as ephemeral variants within
species but do not contribute to divergence. The patterns of polymorphism
and divergence at charge-altering amino acid sites are presented for the
Drosophila ND5 gene to examine the evolution of functionally distinct
mutations. Excess charge-altering polymorphism is observed at the carboxyl
terminal and excess charge-altering divergence is detected at the amino
terminal. While the mildly deleterious model fits as a net effect in the
evolution of nonrecombining mitochondrial genomes, these data suggest that
opposing evolutionary pressures may act on different regions of
mitochondrial genes and genomes.
相似文献