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991.
Balabanli B Türközkan N Balabanli S Erdamar H Akmansu M 《Molecular and cellular biochemistry》2006,286(1-2):103-105
The aim of this investigation was to determine whether pre-administration of vitamin A will be effective in preventing the radiation-induced decline in MPO-H2O2 system and the end product of reactive nitrogen species (NOx) in guinea pig. Animals were subjected to 612 cG of radiation and polimorfonuclear leukocytes were isolated and then NOx and myeloperoxidase activity were measured. In irradiated animals, a marked decrease in NOx level and myeloperoxidase activity have been found compared to control (p = 0.001 and p < 0.000 respectively). The application of vitamin A significantly improved the radiation-induced decrease (for both p < 0.00). In conclusion pre-treatment of vitamin A is efficient to protect against radiation induced alteration in polimorfonuclear leukocyte. 相似文献
992.
Erasmus Schneider Barbara Müller Richard Schindler 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,741(1):77-85
Two heat-sensitive (arrested in G1 at 39.5°C) and two cold-sensitive (arrested in G1 at 33°C) clonal cell-cycle mutants that had been isolated from the same clone (K 21), of the murine mastocytoma P-815 cell line, were tested for thymidine kinase (EC 2.7.1.21) activity. After shift of mutant cells to the nonpermissive temperature, thymidine kinase activity decreased, and minimal levels (i.e., less than 3% of those observed for ‘wild-type’ K 21 cells at the respective temperature) were attained within 16 h in heat-sensitive and after 3–4 days in cold-sensitive mutants, which is in good agreement with kinetics of accumulation of heat-sensitive and cold-sensitive cells in G1 phase. After return of arrested mutant cells to the permissive temperature, thymidine kinase of heat-sensitive cells increased rapidly and in parallel with entry of cells into the S phase. In cultures of cold-sensitive cells, however, initiation of DNA synthesis preceded the increase of thymidine kinase activity by approx. one cell-cycle time. Thymidine kinase activities in revertants of the heat-sensitive and cold-sensitive mutants were similar to those of ‘wild-type’ cells. In ‘wild-type’ K 21 cells incubated at 39.5°C, thymidine kinase activity was approx. 30% of that at 33°C. This difference is attributable, at least in part, to a higher rate of inactivation of the enzyme at 39.5°C, as determined in cultures incubated with cycloheximide. The rapid increase of thymidine kinase activity that occurred after shift of K 21 cells and of arrested heat-sensitive mutant cells from 39.5°C to 33°C was inhibited by actinomycin D and cycloheximide. 相似文献
993.
The ultrastructure of astrocytes in an organotypic slice culture of the rat visual cortex was investigated using ultrathin sections and freeze-fracture replicas. After a culture period of 9–15 days, a glial scaffold formed that separated the bulk of the slice neuropil from the medium and the underlying plasma clot. However, the glial cells and processes did not build a dense barrier but allowed the outgrowth of neurites. A basal lamina covering the medium-oriented surface of the astrocytes was not found. In freeze-fracture replicas, orthogonal arrays of particles (OAP) were characteristic components of astrocytic membranes. The OAP density in membranes bordering the medium was 35±13 OAP/m2, corresponding to 2.5% of this membrane area; the OAP density in membranes within the slice neuropil was 22±12 OAP/2, corresponding to 1.4% of this membrane area. Although the difference was significant, it was greatly reduced when comparing OAP densities in endfoot and non-endfoot membranes in vivo. Another mode of polarity was recognized in astrocytes of the organotypic slice culture. In membranes of astrocytes bordering upon the medium, the density of non-OAP intramembranous particles (IMP) was clearly higher (1130±136 IMP/ m2) than in membranes of astrocytes in the center of the slice (700±172 IMP/m2). This pronounced IMP-related polarity was observed neither in vivo nor in cultured astrocytes. The present study suggests, together with data from the literature, that the distribution of astrocytic OAP across the cell surface is influenced by the existence of a basal lamina and neuronal activity, and that astrocytes possess a more remarkable plasticity of membrane structure than previously suspected. 相似文献
994.
Peter Müller Karl-Rudolf Erlemann Karin Müller Juan J. Calvete Edda Töpfer-Petersen Kathleen Marienfeld A. Herrmann 《European biophysics journal : EBJ》1998,27(1):33-41
PDC-109 is the major protein of bovine seminal plasma. It binds to the bovine sperm surface at ejaculation and modulates
sperm capacitation. PDC-109 displays phosphorylcholine- and heparin-binding activities which are thought to account for its
sperm surface coating and glycosaminoglycan-induced sperm capacitating activities, respectively. We have characterized the
interaction of isolated PDC-109 with membranes of phospholipid vesicles using a biophysical approach. Our results show that
PDC-109 interacts not only with the solvent-exposed phosphorylcholine head group but also with the hydrophobic core of liposomes.
Binding of PDC-109 to membranes is a very rapid, biphasic process with half times of less than one second. Maximal binding
of PDC-109 to small unilamellar vesicles was achieved with a stoichiometric ratio of 10–11 phosphatidylcholine molecules/PDC-109
molecule. Incorporation of phosphatidylethanolamine or phosphatidylserine into phosphatidylcholine vesicles reduced the binding
of PDC-109, suggesting that both the density of phosphorylcholine groups and the surface charge determine the interaction
of the seminal plasma protein with the surface of the membrane. Electron spin resonance measurements showed that binding of
PDC-109 to phosphatidylcholine vesicles caused a rigidification of the membrane. The relevance of the data for describing
the role of PDC-109 in the modulation of sperm capacitation is discussed.
Received: 16 June 1997 / Accepted: 10 September 1997 相似文献
995.
John L. Markley Ad Bax Yoji Arata C. W. Hilbers Robert Kaptein Brian D. Sykes Peter E. Wright Kurt Wüthrich 《Journal of biomolecular NMR》1998,12(1):1-23
The recommendations presented here are designed to support easier communication of NMR data and NMR structures of proteins and nucleic acids through unified nomenclature and reporting standards. Much of this document pertains to the reporting of data in journal articles; however, in the interest of the future development of structural biology, it is desirable that the bulk of the reported information be stored in computer-accessible form and be freely accessible to the scientific community in standardized formats for data exchange. These recommendations stem from an IUPAC-IUBMB-IUPAB inter-union venture with the direct involvement of ICSU and CODATA. The Task Group has reviewed previous formal recommendations and has extended them in the light of more recent developments in the field of biomolecular NMR spectroscopy. Drafts of the recommendations presented here have been examined critically by more than 50 specialists in the field and have gone through two rounds of extensive modification to incorporate suggestions and criticisms. 相似文献
996.
J Müller 《Biochimica et biophysica acta》1985,830(1):95-100
Hydroxypyrenetrisulfonate binds to pig mitochondrial malate dehydrogenase (L-malate: NAD+ oxidoreductase, EC 1.1.1.37) in the presence and absence of coenzymes with a stoichiometry of one dye molecule/enzyme subunit. Binding is competitive with substrates and known substrate analogs as well as with squaric acid, a newly detected analog forming a ternary complex with enzyme/NAD+ similar to enzyme/NAD+/sulfite. Displacement of hydroxypyrenetrisulfonate by substrates and analogs was used to determine dissociation constants of binary and ternary complexes. Binary complexes form with dissociation constants of about 10 mM. They may be important for kinetic studies at high substrate concentrations where oxaloacetate inhibition and malate activation have been described. 相似文献
997.
A new triterpenoid glycoside containing an amino sugar moiety has been isolated from Pithecellobium cubense and P. arboreum and identified as O(3)- (2-acetylamino-2-deoxy-β-d-glucopyranosyl)oleanolic acid. β-d-Glucopyranosyl-α-spinasterol was also obtained from P. cubense. 相似文献
998.
999.
cAMP serves as a second messenger in virtually all organisms. The most wide-spread class of cAMP-generating enzymes are the class III adenylyl cyclases. Most class III adenylyl cyclases are multi-domain proteins. The catalytic domains exclusively work as dimers, catalysis proceeds at the dimer interface, so that both monomers provide catalytic residues to each catalytic center. Inspection of amino acid sequence profiles suggests a division of the class III adenylyl cyclases in to four subclasses, class IIIa–IIId. Genome projects and postgenomic analysis have provided novel aspects in terms of catalysis and regulation. Alterations in the canonical catalytic residues occur in all four subclasses suggesting a plasticity of the catalytic mechanisms. The vast variety of additional, probably regulatory modules found in class III adenylyl cyclases obviously reflects a large collection of regulatory inputs the catalytic domains have adapted to. The large versatility of class III adenylyl cyclase catalytic domains remains a major scientific challenge. 相似文献
1000.
Robert Müller Christoph Nowicki Wilhelm Barthlott Pierre L. Ibisch 《Biodiversity and Conservation》2003,12(10):2005-2024
Analyses of species diversity and endemism patterns provide vital inputs for conservation planning. Therefore, it is an important dilemma of biodiversity conservation that in very diverse but poorly studied tropical countries those patterns can hardly be considered. Consequently, there is an urgent need to develop prediction models that make the best use of existing data on species distribution and that can give hints on spatial conservation priorities. This paper presents the results of a pilot study on the diversity of the orchid subtribe Pleurothallidinae (331 mapped species) in the Andean rain forests of Bolivia. Results of a taxon-based mapping methodology, using abiotic (humidity and temperature, the latter indicated by altitude) and historical factors (taken into account as distance from collection localities) that determine species ranges, are compared with outcomes of an inventory-based mapping approach. The patterns of taxon-based diversity and endemism show a strong correlation with the distribution of sample localities. The inventory-based approach is more reliable, but it is interesting to apply both mapping methods in order to make a critical interpretation and comparison that facilitates some valuable conservation recommendations. We end with concrete conclusions for conservation planning and action. 相似文献