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排序方式: 共有176条查询结果,搜索用时 15 毫秒
1.
Construction of an Obligate Photoheterotrophic Mutant of the Cyanobacterium Synechocystis 6803 : Inactivation of the psbA Gene Family 总被引:14,自引:0,他引:14 下载免费PDF全文
psbA in Synechocystis 6803 was found to belong to a small multigene family with three copies. The psbA gene family was inactivated in vitro by insertation of bacterial drug resistance markers. Inactivation of all three genes resulted in a transformant that is unable to grow photosynthetically but can be cultured photoheterotrophically. This mutant lacks oxygen evolving capacity but retains photosystem I activity. Room temperature measurements of chlorophyll a fluorescence induction demonstrated that the transformant exhibits a high fluorescence yield with little or no variable fluorescence. Immunoblot analyses showed complete loss of the psbA gene product (the DI polypeptide) from thylakoid membranes in the transformant. However, the extrinsic 33 kilodalton polypeptide of the water-splitting complex of photosystem II, is still present. The results indicate that assembly of a partial photosystem II complex may occur even in the absence of the intrinsic D1 polypeptide, a protein implicated as a crucial component of the photosystem II reaction center. 相似文献
2.
Water oxidation in photosystem II: from radical chemistry to multielectron chemistry 总被引:8,自引:0,他引:8
G T Babcock B A Barry R J Debus C W Hoganson M Atamian L McIntosh I Sithole C F Yocum 《Biochemistry》1989,28(25):9557-9565
3.
Directed mutagenesis indicates that the donor to P+680 in photosystem II is tyrosine-161 of the D1 polypeptide 总被引:12,自引:0,他引:12
Photosystem II contains two redox-active tyrosines. One of these, YZ, reduces the reaction center chlorophyll, P680, and transfers the oxidizing equivalent to the oxygen-evolving complex. The second, YD, has a long-lived free radical state of unknown function. We recently established that YD is Tyr-160 of the D2 polypeptide by site-directed mutagenesis of a psbD gene in the unicellular cyanobacterium Synechocystis 6803 [Debus, R. J., Barry, B. A., Babcock, G. T., & McIntosh, L. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 427-430]. YZ is most likely the symmetry-related Tyr-161 of the D1 polypeptide. To test this hypothesis, we have changed Tyr-161 to phenylalanine by site-directed mutagenesis of a psbA gene in Synechocystis. The resulting mutant assembles PSII, as judged by its ability to produce the stable Y+D radical, but is unable to grow photosynthetically and exhibits altered fluorescence properties. The nature of the fluorescence change indicates that forward electron transfer to P+680 is disrupted in the mutant. These results provide strong support for our identification of Tyr-161 in the D1 polypeptide with YZ. 相似文献
4.
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 下载免费PDF全文
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
5.
Monoclonal antibodies specific for glial fibrillary acidic (GFA) protein and for each of the neurofilament triplet polypeptides 总被引:27,自引:0,他引:27
A panel of 10 mouse monoclonal antibodies specific for glial fibrillary acidic protein (GFA) has been isolated using porcine GFA as antigen. Although all antibodies recognize GFA purified from porcine spinal cord in the western blot technique, they can be subdivided into at least three groups on the basis of their reactivity against defined fragments of the molecule. Immunofluorescence staining patterns with the monoclonal antibodies performed on tissues and cell lines resemble those reported with conventional polyclonal antibodies directed against GFA. In particular astrocytes and Bergmann glia are strongly stained. In addition mouse monoclonal antibodies specific for either the 200 kd, or the 160 kd, or the 68 kd neurofilament triplet protein have been isolated and characterized. These antibodies are specific for neuronal cells and support conclusions made with similar antigen affinity-purified polyclonal antibodies. The combined set of monoclonal antibodies seems a valuable tool to characterize the different cell types of the nervous system. 相似文献
6.
David A. Fuccillo Louis W. Catalano Jr. Flora L. Moder David A. Debus John L. Sever 《Applied microbiology》1969,17(4):619-622
A new disposable micro tissue culture plate was developed and tested for use in virological procedures. Miniature mammalian cell cultures (minicultures) were grown in these plates. Each plate contained 96 circular cultures in flat wells (7 mm in diameter). Replicate titrations of a number of viruses were performed in various tissues. Excellent reproducibility was demonstrated. Mean infectivity titers determined by miniculture methods were generally within 0.6 log10/ml of macro tube titrations. Standard tissue culture assay techniques such as hemadsorption, interference titration, and microneutralization were easily carried out with this method and were very reproducible. Development of this noncytotoxic disposable micro tissue culture plate now permits the routine performance of rapid, reliable, and reproducible tissue culture tests at a very significant reduction in cost and labor. 相似文献
7.
8.
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
9.
10.
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.
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