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排序方式: 共有75条查询结果,搜索用时 15 毫秒
1.
Hardies SC; Martin SL; Voliva CF; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1986,3(2):109-125
2.
The electronic structure of Fe2+ in reaction centers from Rhodopseudomonas sphaeroides. II. Extended x-ray fine structure studies. 总被引:4,自引:0,他引:4
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Extended x-ray absorption fine structure (EXAFS) studies were performed on reaction centers (RC) of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26. RC containing two, one, and no quinones (2Q, 1Q, 0Q) samples were studied. The average ligand distance of the first coordination shell was determined to be 2.10 +/- 0.02 A with a more distant shell at 4.14 +/- 0.05 A. The Fe2+ site in RC was found to have a very large structural disorder parameter, from which a spread in ligand distance per iron site of approximately +/- 0.1 A was deduced. The most likely coordination number of the first shell is six, with a mixture of oxygens and nitrogens as ligands. The edge absorption results are consistent with the Fe2+ being in distorted octahedral environment. The EXAFS spectra of the 2Q and 1Q samples with and without O-phenanthroline were found to be the same. This indicates that either the secondary quinone and o-phenanthroline do not bind to Fe2+ or that they replace an equivalent ligand. The 0Q sample showed a 12% decrease in the EXAFS amplitude, which was restored upon addition of o-phenanthroline. These results can be explained by either a loss of a ligand or a severe conformational change when the primary quinone was removed. 相似文献
3.
The location of redox centers in biological membranes determined by resonance x-ray diffraction. I. Observation of the resonance effect 总被引:3,自引:0,他引:3
J Stamatoff P Eisenberger J K Blasie J M Pachence A Tavormina M Erecinska P L Dutton G Brown 《Biochimica et biophysica acta》1982,679(2):177-187
We have developed resonance X-ray diffraction methods to locate for the first time intrinsic metal atoms associated with redox centers within biological membrane systems. The study of membranes containing dilute concentrations of resonant scatterers has been made possible by the development of synchrotron radiation sources of X-rays. The technique permits altering the scattering power of a particular atom relative to others by varying the incident X-ray energy. Thus, this method may be used to locate a metal atom within a complex integral protein without chemical modification of the membrane. We present resonance diffraction data taken with synchroton radiation for two different membrane systems: cytochrome oxidase incorporated into lipid vesicles and a photosynthetic reaction center-cytochrome c complex also reincorporated into lipid vesicles. 相似文献
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We present a new method for the determination of structural parameters in biological membranes. Recording the continuous scattering of heavy-atom labeled membranes and applying elementary Fourier methods we obtain the scattering of the heavy-atom distribution alone. The details of this distribution are explored by developing a simple model and testing for cases relevant to biological membranes. We find that the intensity distribution is highly sensitive to many key parameters. The increased signal from heavy-atom labeling and the use of an improved x-ray system make it possible to record patterns from dilute membrane suspensions. Thus determination of these parameters is possible in the same environment where many membrane biochemical studies are performed. Application of the method is made to a model lipid bilayer membrane, dipalmitoyl phosphatidylcholine by labeling with UO2++ ions. We determine the precise distance between UO2++ layers on either side of the membrane as well as the width of the label on each side. This determination permits estimation of phosphate separation across single labeled bilayers in an aqueous suspension. 相似文献
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Roberto?H?Higa Roberto?C?Togawa Arnaldo?J?Montagner Juliana?CF?Palandrani Igor?KS?Okimoto Paula?R?Kuser Michel?EB?Yamagishi Adauto?L?Mancini Goran?NeshichEmail author 《BMC bioinformatics》2004,5(1):107
Background
The integration of many aspects of protein/DNA structure analysis is an important requirement for software products in general area of structural bioinformatics. In fact, there are too few software packages on the internet which can be described as successful in this respect. We might say that what is still missing is publicly available, web based software for interactive analysis of the sequence/structure/function of proteins and their complexes with DNA and ligands. Some of existing software packages do have certain level of integration and do offer analysis of several structure related parameters, however not to the extent generally demanded by a user. 相似文献9.
Interest in the use of low-copy nuclear genes for phylogenetic analyses of
plants has grown rapidly, because highly repetitive genes such as those
commonly used are limited in number. Furthermore, because low- copy genes
are subject to different evolutionary processes than are plastid genes or
highly repetitive nuclear markers, they provide a valuable source of
independent phylogenetic evidence. The gene for granule-bound starch
synthase (GBSSI or waxy) exists in a single copy in nearly all plants
examined so far. Our study of GBSSI had three parts: (1) Amino acid
sequences were compared across a broad taxonomic range, including grasses,
four dicotyledons, and the microbial homologs of GBSSI. Inferred structural
information was used to aid in the alignment of these very divergent
sequences. The informed alignments highlight amino acids that are conserved
across all sequences, and demonstrate that structural motifs can be highly
conserved in spite of marked divergence in amino acid sequence. (2)
Maximum-likelihood (ML) analyses were used to examine exon sequence
evolution throughout grasses. Differences in probabilities among
substitution types and marked among-site rate variation contributed to the
observed pattern of variation. Of the parameters examined in our set of
likelihood models, the inclusion of among-site rate variation following a
gamma distribution caused the greatest improvement in likelihood score. (3)
We performed cladistic parsimony analyses of GBSSI sequences throughout
grasses, within tribes, and within genera to examine the phylogenetic
utility of the gene. Introns provide useful information among very closely
related species, but quickly become difficult to align among more divergent
taxa. Exons are variable enough to provide extensive resolution within the
family, but with low bootstrap support. The combined results of amino acid
sequence comparisons, maximum-likelihood analyses, and phylogenetic studies
underscore factors that might affect phylogenetic reconstruction. In this
case, accommodation of the variable rate of evolution among sites might be
the first step in maximizing the phylogenetic utility of GBSSI.
相似文献
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