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排序方式: 共有147条查询结果,搜索用时 15 毫秒
1.
S Carbajo E Carbajo-Pérez J L Hernández R Vázquez J C Carvajal 《Histology and histopathology》1991,6(4):497-501
An immunocytochemical study of the epithelial lining of naturally occurring cysts in the rat intermediate lobe (IL) has been carried out. Paraffin-embedded sections, in which cysts were identifiable, were treated either with anti-serotonin or anti-S-100 protein sera. S-100-positive cells were intermingled with glandular cells surrounding the cyst lumen. These S-100-positive cells sent slender cytoplasmic processes as if to cover the apical surface of neighbouring cells. Rarely were 5-HT-immunopositive cells seen in the cyst epithelial lining. Most cells of the marginal layer of the IL were found reactive either to an S-100 or a-5-HT serum. The presence of an epithelial lining positive to S-100 protein sera is in keeping with the notion that cysts in the IL might form as evaginations of the epithelial lining of the pituitary cleft. The lack of correspondence between 5-HT-positive cells in the marginal layer and the cyst lining is controversial. A peculiar spatial relationship of 5-HT cells with the vascular network of the IL is suggested. 相似文献
2.
Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium 总被引:13,自引:9,他引:4
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Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel. 相似文献
3.
Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal 总被引:10,自引:9,他引:1
We have developed a new approach to the measurement of phylogenetic signal
in character state matrices called relative apparent synapomorphy analysis
(RASA). RASA provides a deterministic, statistical measure of natural
cladistic hierarchy (phylogenetic signal) in character state matrices. The
method works by determining whether a measure of the rate of increase of
cladistic similarity among pairs of taxa as a function of phenetic
similarity is greater than a null equiprobable rate of increase. Our
investigation of the utility and limitations of RASA using simulated and
bacteriophage T7 data sets indicates that the method has numerous
advantages over existing measures of signal. A first advantage is
computational efficiency. A second advantage is that RASA employs known
methods of statistical inference, providing measurable sensitivity and
power. The performance of RASA is examined under various conditions of
branching evolution as the number of characters, character states per
character, and mutations per branch length are varied. RASA appears to
provide an unbiased and reliable measure of phylogenetic signal, and the
general approach promises to be useful in the development of new techniques
that should increase the rigor and reliability of phylogenetic estimates.
相似文献
4.
5.
Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis) 总被引:4,自引:0,他引:4
Analysis of the heat-shock proteins (hsps) of six closely related species
of Poeciliopsis demonstrated the existence of biochemical diversity in the
hsp100, hsp70, hsp60, and hsp30 protein families among species. Each
species expressed five to seven hsp70-related isoforms. Constitutive 70-kD
isoforms were identical among species, but four different patterns of
heat-inducible isoforms were seen in these six species. Members of the
hsp70 family of molecular chaperones are included among the most highly
conserved proteins known, and the possibility of variation in hsp70 among
closely related species has rarely been addressed. The hsp30 family is
known to be less conserved than the hsp70 family, and, as expected, the
Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30
isoforms characteristic of a particular species were unique to that
species. Hsp100 and hsp60 were identical in five of the species, but
alternate isoforms were found in P. monacha. The small size and limited
geographical distribution of the P. monacha population have probably
contributed to the uniqueness of the monacha pattern. Two of the species
were shown to acquire thermotolerance, the ability to withstand normally
lethal temperatures when subjected to a gradual temperature increase.
Rapid-heating protocols commonly used to establish critical thermal maxima
of organisms do not include this inducible component of thermoresistance
and therefore do not adequately assess an organism's capacity to withstand
thermal stress.
相似文献
6.
Variation in heat shock proteins within tropical and desert species of poeciliid fishes 总被引:8,自引:0,他引:8
Norris CE; diIorio PJ; Schultz RJ; Hightower LE 《Molecular biology and evolution》1995,12(6):1048-1062
The 70-kilodalton heat shock protein (hsp70) family of molecular
chaperones, which contains both stress-inducible and normally abundant
constitutive members, is highly conserved across distantly related taxa.
Analysis of this protein family in individuals from an outbred population
of tropical topminnows, Poeciliopsis gracilis, showed that while
constitutive hsp70 family members showed no variation in protein isoforms,
inducibly synthesized hsp70 was polymorphic. Several species of
Poeciliopsis adapted to desert environments exhibited lower levels of
inducible hsp70 polymorphism than the tropical species, but constitutive
forms were identical to those in P. gracilis, as they were in the
confamilial species Gambusia affinis. These differences suggest that
inducible and constitutive members of this family are under different
evolutionary constraints and may indicate differences in their function
within the cell. Also, northern desert species of Poeciliopsis synthesize a
subset of the inducible hsp70 isoforms seen in tropical species. This
distribution supports the theory that ancestral tropical fish migrated
northward and colonized desert streams; the subsequent decrease in
variation of inducible hsp70 may have been due to genetic drift or a
consequence of adaptation to the desert environment. Higher levels of
variability were found when the 30- kilodalton heat shock protein (hsp30)
family was analyzed within different strains of two desert species of
Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In
both cases the distribution of hsp30 isoform diversity was similar to that
seen previously with allozyme polymorphisms.
相似文献
7.
8.
9.
Jesús Rodríguez-Díaz Rodrigo J. Carbajo Antonio Pineda-Lucena Vicente Monedero María J. Yebra 《Applied and environmental microbiology》2013,79(12):3847-3850
AlfB and AlfC α-l-fucosidases from Lactobacillus casei were used in transglycosylation reactions, and they showed high efficiency in synthesizing fucosyldisaccharides. AlfB and AlfC activities exclusively produced fucosyl-α-1,3-N-acetylglucosamine and fucosyl-α-1,6-N-acetylglucosamine, respectively. The reaction kinetics showed that AlfB can convert 23% p-nitrophenyl-α-l-fucopyranoside into fucosyl-α-1,3-N-acetylglucosamine and AlfC at up to 56% into fucosyl-α-1,6-N-acetylglucosamine. 相似文献
10.
Cabezon E Butler PJ Runswick MJ Carbajo RJ Walker JE 《The Journal of biological chemistry》2002,277(44):41334-41341
In Saccharomyces cerevisiae, at least three proteins (IF(1), STF(1), and STF(2)) appear to be involved in the regulation of ATP synthase. Both IF(1) and STF(1) inhibit F(1), whereas the proposed function for STF(2) is to facilitate the binding of IF(1) and STF(1) to F(1). The oligomerization properties of yeast IF(1) and STF(1) have been investigated by sedimentation equilibrium analytical ultracentrifugation and by covalent cross-linking. Both techniques confirm that IF(1) and STF(1) oligomerize in opposite directions in relation to pH, suggesting that both proteins might regulate yeast F(1)F(0)-ATPase under different conditions. Their effects on bovine F-ATPases are also described. Whereas bovine IF(1) inhibits yeast F(1)-ATPase even better than yeast IF(1) or STF(1), the capability of yeast IF(1) to inhibit the bovine enzyme is very low and decreases with time. Such an effect is also observed in the study of the homologous inhibition of yeast F(1)-ATPase. Yeast inhibitors are not as effective as their bovine counterpart, and the complex seems to dissociate gradually. 相似文献