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21.
Trypsin-releasable glycosaminoglycans from the luminal surface of intact pig aorta were measured following metabolic labelling with35S]sulphate. Chondroitin sulphate was found to be present at a surface density equal to that already established for heparan sulphate (5×1011 chains per cm2). This result was confirmed by X-ray microanalysis of the luminal sulphur content before and after treatment with specific glycosaminoglycan-degrading enzymes. This result implies that approximately half of the luminal surface is occupied by sulphated glycosaminoglycans. 相似文献
22.
H. Daniel 《Biological trace element research》1987,13(1):301-318
Because of the large μ mass compared to the electron mass, the muonic X-rays have energies very suitable for standard γ-ray
spectroscopy (Ge detectors), so every element is easily recognized. By selecting the primary μ energies appropriately any
part of the specimen, also well inside, can be nondestructively investigated. On the other hand, surface layers may be analyzed.
Accuracies of quantitative analyses are 1% of the atomic abundance of the element in question in favorite cases. Results on
applications in nuclear medicine and surface physics are presented, and ways of improving the muon flux density are discussed. 相似文献
23.
Barry M. Gordon 《Biological trace element research》1987,12(1):153-159
Information concerning the chemical state of trace elements in biological systems generally has not been available. Such information
for toxic elements and metals in metalloproteins could prove extremely valuable in the elucidation of their metabolism and
other biological processes. The shielding of core electrons by binding electrons affect the energy required for creating inner-shell
holes. Furthermore, the molecular binding and symmetry of the local environment of an atom affect the absorption spectrum
in the neighborhood of the absorption edge. X-ray absorption near-edge structure (XANES) using synchrotron radiation excitation
can be used to provide chemical speciation information for trace elements at concentrations as low as 10 ppm. The structure
and position of the absorption curve in the region of an edge can yield vital data about the local structure and oxidation
state of the trace element in question. Data are most easily interpreted by comparing the observed edge structure and position
with those of model compounds of the element covering the entire range of possible oxidation states. Examples of such analyses
will be reviewed. 相似文献
24.
Many biomedical experiments require the qualitative and quantitative localization of trace elements with high sensitivity
and good spatial resolution. The feasibility of measuring the chemical form of the elements, the time course of trace element
metabolism, and conducting experiments in living biological systems are also important requirements for biological trace element
research. Nuclear analytical techniques that employ ion or photon beams have grown in importance in the past decade and have
led to several new experimental approaches. Some of the important features of these methods are reviewed here along with their
role in trace element research. Examples of their use are given to illustrate potential for new research directions. It is
emphasized that the effective application of these methods necessitates a closely integrated multidisciplinary scientific
team. 相似文献
25.
A particle-induced X-ray emission (PIXE) analysis method is presented, which allows measurement of eight elements (i.e., K,
Ca, Mn, Fe, Cu, Zn, Se, and Rb) in human brain samples of only a few mg dry weight. The precision and accuracy of the method
were investigated by analyzing animal brain matter with both PIXE and instrumental neutron activation analysis (INAA). The
method was applied to measure the 8 elements in 46 different regions of 3 human brains. The sections analyzed originated from
either the left or the right cerebral hemisphere, brain stem, and cerebellum. For one of the brains, sections were also analyzed
from 26 corresponding regions of both hemispheres. For all elements, similar concentrations were found in the corresponding
areas of the left and right sides of the brain. The concentrations (in μg/g dry weight) of the elements K, Fe, Cu, Zn, Se,
and Rb were consistently higher in cortical structures than in white matter. Deep nuclei and brain stem, which have a mixed
composition, showed intermediate values for K, Zn, Se, and Rb. A hierarchical cluster analysis indicated that the various
brain regions clustered into two large groups, one comprising gray and mixed matter regions and the other, white and mixed
matter brain areas. 相似文献
26.
Summary A complete ribosomal DNA (rDNA) repeat unit has been cloned from the genome of Pisum sativum (garden pea) and used to construct a map containing a total of 58 cleavage sites for 23 different restriction enzymes. Regions encoding 18s and 25s ribosomal RNA (rRNA) were identified by R-loop analysis. A 180 bp sequence element is repeated eight times in the intergenic nontranscribed spacer (NTS) region, as defined by eight evenly spaced RsaI cleavage sites. Sequence heterogeneity among these elements (subrepeats) is indicated by the presence of an NcoI site within the five RsaI subrepeats distal to the 25s rRNA gene but not in the three subrepeats proximal to this gene, and also by the presence of an additional RsaI cleavage site in one subrepeat.The approximately 4000 copies of the rDNA repeat in the pea nuclear genome show considerable heterogeneity with respect to the length of the NTS region, and differences are also frequently observed between different genotypes. In both cases the length variation appears to be due primarily to differences in the number of subrepeat elements.Comparison of rDNA restriction maps for two pea genotypes separated for hundreds or perhaps thousands of generations reveals that they contain many rDNA identical repeat units. This data is consistent with the view that new rDNA variants are fixed only infrequently in the evolution of a species.Differences also exist between the rDNA repeats of a single genotype with respect to the degree of base modification at certain restriction sites. A large number of sites known to exist in the pea rDNA clone are not cleaved at all in genomic rDNA, or are cleaved in only some copies of the rDNA repeat. We believe these examples of incomplete cleavage results mostly from methylation, although it is difficult to rule out the possibility of sequence variation in all cases. Most putative modifications are best interpreted in terms of cytosine methylation in CG and CXG sequences, but at least one example is more consistent with adenine methylation.We also have constructed a more detailed restriction map of the wheat rDNA clone pTA71 and present a comparison of this map to our map of pea, pumpkin, and wheat in order to assess the amount of useful evolutionary information that can be obtained by comparison of such maps. 相似文献
27.
28.
Rapid immunofluorescent determination of cells in the S phase in pea root meristems: An alternative to autoradiography 总被引:2,自引:0,他引:2
Photosystem II (PS II) activity and the localization of ribulose-l,5-bisphosphate (RuBP) carboxylase (EC 4.1.1.39) were studied in primary leaves of young maize plants ( Zea mays L. cv. Fronica) by tetra-nitro-blue-tetrazoliumchloride reduction and immunolocalization, respectively. In tissue of 3-day-old plants all chloroplasts were structurally identical. From day 4 they developed into their typical appearance of mesophyll and bundle sheath chloroplasts. First PS II-activity was present in both types of chloroplasts. From day 4 it disappeared in bundle sheath chloroplasts concomitant with the loss of grana. RuBP carboxylase on the other hand was only present in bundle sheath chloroplasts at all stages of development. Thus, the control of the development of the photosystems and the Calvin cycle enzymes seem to differ. 相似文献
29.
The effects of structural analogues, excitatory amino acids and certain drugs on spontaneous and potassium-stimulated exogenous taurine and GABA release were investigated in mouse cerebral cortex slices using a superfusion system. Spontaneous efflux of both amino acids was rather slow but could be enhanced by their uptake inhibitors. Taurine efflux was facilitated by exogenous taurine, hypotaurine, -alanine and GABA, whereas GABA, nipecotic acid and homotaurine effectively enhanced GABA release. The stimulatory potency of the analogues closely corresponded to their ability to inhibit taurine and GABA uptake, respectively, indicating that these efflux processes could be mediated by the carriers operating outwards. Glutamate induced GABA release, whereas taurine efflux was potentiated by aspartate, glutamate, cysteate, homocysteate and kainate. The centrally acting drugs, including GABA agonists and antagonists, as well as the proposed taurine antagonist TAG (6-aminomethyl-3-methyl-4H-1,2,4-benzothiadiazine-1,1-dioxide), had no marked effects on spontaneous taurine and GABA release. Potassium ions stimulated dosedependently both taurine and GABA release from the slices, the responses of taurine being strikingly slow but sustained. Exogenous GABA and nipecotic acid accelerated the potassium-stimulated GABA release, whereas picrotoxin and bicuculline were ineffective. The potassium-stimulated taurine release was unaltered or suppressed by exogenous taurine and analogues, differing in this respect from GABA release. The apparent magnitude of the depolarization-induced GABA release is thus influenced by the function of membrane transport sites, but the same conclusion cannot be drawn with regard to taurine. Haloperidol and imipramine were able to affect the evoked release of both taurine and GABA. 相似文献
30.
Generation of potential structures for the G-domain of chloroplast EF-Tu using comparative molecular modeling 总被引:2,自引:0,他引:2
Comparative molecular modeling has been used to generate several possible structures for the G-domain of chloroplast elongation factor Tu (EF-Tu(chl)) based on the crystallographic data of the homologous E. coli protein. EF-Tu(chl) contains a 10 amino acid insertion not present in the E. coli protein and this region has been modeled based on its predicted secondary structure. The insertion appears to lie on the surface of the protein. Its orientation could not be determined unequivocally but several likely structures for the nucleotide binding domain of EF-Tu(chl) have been developed. The effects of the presence of water in the Mg2+ coordination sphere and of the protonation state of the GDP ligand on the conformation of the guanine nucleotide binding site have been examined. Relative binding constants of several guanine nucleotide analogs for EF-Tu(chl) have been obtained. The interactions between EF-Tu(chl) and GDP predicted to be important by the models that have been developed are discussed in relation to the nucleotide binding properties of this factor and to the interactions proposed to be important in the binding of guanine nucleotides to related proteins. 相似文献