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排序方式: 共有183条查询结果,搜索用时 93 毫秒
1.
Levans produced by four Zymomonas mobilis strains showed antitumour activity against sarcoma 180 and Ehrlich carcinoma in Swiss albino mice. Levans from two strains (ZAP and CP4) had the highest effects. NMR analysis showed that the polymers were composed only of fructose units. The results suggested that the antineoplasic effect is associated to the polysaccharide molecular weight and that a particular molecular weight range may be responsible for this effect. 相似文献
2.
3.
Single-channel analysis of inactivation-defective rat skeletal muscle sodium channels containing the F1304Q mutation. 总被引:3,自引:0,他引:3
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J H Lawrence D W Orias J R Balser H B Nuss G F Tomaselli B O''Rourke E Marban 《Biophysical journal》1996,71(3):1285-1294
The intracellular linker between domains III and IV of the voltage-gated Na channel mediates fast inactivation. Targeted alteration of one or more of a triplet of hydrophobic amino acids within this linker region results in a marked slowing in the decay of ionic current. The mechanism of this defective inactivation was explored in rat skeletal muscle sodium channels (mu 1) containing the F1304Q mutation in Xenopus laevis oocytes with and without coexpression of the rat brain beta 1 subunit. Cell-attached single-channel patch-clamp recordings revealed that the mu 1-F1304Q channel reopens multiple times with open times that are prolonged compared with those of the wild-type channel. Coexpression of the beta 1 subunit stabilized a dominant nonbursting gating mode and accelerated the activation kinetics of mu 1-F1304Q but did not modify mean open time or fast-inactivation kinetics. A Markov gating model incorporating separate fast- and slow-inactivation particles reproduced the results by assuming that the F1304Q mutation specifically influences transitions to and from fast-inactivated states. These effects are independent of interactions of the mutant channel with the beta 1 subunit and do not result from a change in modal gating behavior. These results indicate that F1304Q mutant channels can still enter the inactivated state but do so reversibly and with altered kinetics. 相似文献
4.
Polygalacturonase-inhibiting protein accumulates in Phaseolus vulgaris L. in response to wounding, elicitors and fungal infection 总被引:7,自引:0,他引:7
Carl W. Bergmann Yuki Ito Darrell Singer Peter Albersheim Alan G. Darvill Nicole Benhamou Laurence Nuss Giovanni Salvi Felice Cervone Giulia De Lorenzo 《The Plant journal : for cell and molecular biology》1994,5(5):625-634
Polygalacturonase-inhibiting protein (PGIP) is a cell wall-associated protein that specifically binds to and inhibits the activity of fungal endopolygalacturonases. The Phaseolus vulgaris gene encoding PGIP has been cloned and characterized. Using a fragment of the cloned pgip gene as a probe in Northern blot experiments, it is demonstrated that the pgip mRNA accumulates in suspension-cultured bean cells following addition of elicitor-active oligogalacturonides or fungal glucan to the medium. Rabbit polyclonal antibodies specific for PGIP were generated against a synthetic peptide designed from the N-terminal region of PGIP; the antigenicity of the peptide was enhanced by coupling to KLH. Using the antibodies and the cloned pgip gene fragment as probes in Western and Northern blot experiments, respectively, it is shown that the levels of PGIP and its mRNA are increased in P. vulgaris hypocotyls in response to wounding or treatment with salicylic acid. Using gold-labeled goat-anti-rabbit secondary antibodies in EM studies, it has also been demonstrated that, in bean hypocotyls infected with Colletotrichum lindemuthianum, the level of PGIP preferentially increases in those cells immediately surrounding the infection site. The data support the hypothesis that synthesis of PGIP constitutes an active defense mechanism of plants that is elicited by signal molecules known to induce plant defense genes. 相似文献
5.
Variation in the ribosomal internal transcribed spacers (ITS1 and ITS2) among eight taxa of the Mimulus guttatus species complex 总被引:1,自引:0,他引:1
The internal transcribed spacer region (ITS1 and ITS2) of the 18S-25S
nuclear ribosomal DNA sequence and the intervening 5.8S region were
sequenced from three individuals in each of eight taxa of the Mimulus
guttatus species complex. Three discrete variants, or "types," of ITS
sequences were found, among which 30%-40% of sites differed, compared with
1%-2% within types. Dot plots indicate that these types were not related by
conspicuous rearrangements or inversions. More than one ITS type was often
found in the same taxon, and two of three ITS types span species
boundaries, indicating their presence prior to speciation. These ITS
sequences showed essentially no positional homology with the nearest
sequenced relative, tomato. In contrast, the 5.8S region was relatively
unvaried, with 8 of 162 sites varied in the sample among all eight taxa.
The phylogeny inferred by the most common ITS sequence type, rooted by the
two other ITS types, agreed with isozymes in showing the distinctness of M.
nudatus, M. laciniatus, and M. tilingii from the other five taxa.
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6.
Using Hypoviruses to Probe and Perturb Signal Transduction Processes Underlying Fungal Pathogenesis 总被引:6,自引:0,他引:6
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![点击此处可从《The Plant cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Nuss DL 《The Plant cell》1996,8(10):1845-1853
7.
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.
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8.
The m7(G(5')pppN-pyrophosphatase activity previously detected in HeLa cells has been further characterized. Results from DEAE-cellulose column chromatography and polyacrylamide gel electrophoresis under nondenaturing conditions revealed only one enzyme activity in HeLa cell extracts which was capable of selectively hydrolyzing m7G(5')pppN to yield m7pG + ppN (where N = 2'-O-methylated or unmethylated ribonucleosides or oligonucleotides of up to 8 to 10 nucleosides in length). The majority (approximately 95%) of this activity was found in the cytoplasmic extract but appeared not to be associated with the lysosomal fraction. m7G(5')pppG was hydrolyzed by the partially purified enzyme in the absence of divalent cations at a pH optimum of 7.5 and a temperature optimum of 45 degrees, with a Michaelis constant (Km) of 1.7 micronM. Sedimentation analysis and gel filtration showed the molecular weight of the enzyme as approximately 81,000. Inhibition studies testing the effect of a number of prospective substrates on the rate of m7G(5')pppG hydrolysis have confirmed the importance of the methyl moiety at the N7 position of guanosine for enzyme-substrate interaction. Furthermore, the trimethylated guanosine-containing 5'-terminal structure derived from U-2 RNA was found not to serve as substrate, and 7-methylinosine, unlike 7-methylguanosine, was not an effective inhibitor of m7G(5')pppG hydrolysis. Thus, the 2-amino group of the 7-methylguanosine portion of m7G(5')pppN is also important for substrate interaction with this specific pyrophosphatase. 相似文献
9.
A purification scheme has been developed for the m7G(5')pppN-pyrophosphatase from human placenta. The 1400-fold purified placental enzyme exhibited physical and enzymatic properties similar to those previously reported for a crude preparation of the human m7G(5')pppN-pyrophosphatase obtained from HeLa cells. Polyacrylamide gel analysis of enzyme fractions at different stages of purification revealed a Mr = 40,000 polypeptide that increased in relative concentration as the specific activity of the enzyme fractions increased. Copurification of this polypeptide with m7G(5')pppN-pyrophosphatase activity suggests the possibility that the 81,000-dalton native enzyme is a dimer composed of subunits of identical molecular weight. The highly purified placental enzyme, like the crude HeLa enzyme, failed to hydrolyze the cap moiety of intact mRNA even under conditions known to reduce mRNA secondary structure. Moreover, when a series of capped oligonucleotides that differed progressively in chain length by a factor of one nucleotide was tested as substrate, the rate of enzyme-catalyzed cap hydrolysis decreased as the chain length increased. The purified placental enzyme failed to release m7pG from oligonucleotides containing the cap and 3 or more additional nucleotides. These results are discussed in terms of the probable biological function of the m7G(5')pppN-pyrophosphatase. 相似文献
10.