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991.
992.
Acetylcholine, cholinergic agonists and acetylcholinesterase inhibitors significantly decrease the amplitude and frequency of spontaneous longitudinal muscle contractions in Fasciola hepatica. In order of their effects on the inhibition of muscle contractions, the cholinergic agonists can be ranked as nicotine greater than carbachol greater than acetylcholine. High calcium ion concentration also causes a significant inhibition of contractions. Atropine, a cholinergic antagonist that acts on muscarinic receptors, significantly increases the amplitude and frequency of spontaneous contractions and completely reverses the effects of cholinomimetic drugs, including nicotine. In adult F. hepatica, the levels of acetylcholine and its precursor choline are 3.14 +/- 0.55 and 13.75 +/- 3.72 pmol/mg wet weight, respectively. The activities of choline acetyltransferase, specific acetylcholinesterase and the nonspecific cholinesterase are 1.25 +/- 0.19, 238.0 +/- 13.0, and 83.0 +/- 33.0 nmol/hr/mg protein, respectively.  相似文献   
993.
E C B?ttger 《BioTechniques》1989,7(9):925-6, 928-9
The current methods for subcloning entire cDNA libraries usually result in a significant portion of recombinants containing multiple inserts, since in most instances the inserts derived from the library to be subcloned are released as a bulk of self-ligatable DNA fragments. By use of an adaptor strategy, a method is presented to confer noncompatible ends to primarily self-ligatable inserts, resulting in efficient subcloning of entire libraries as single insert recombinants.  相似文献   
994.
Forty-five populations of Pentanema corresponding to seven species included in the Pentanema conyzae clade have been studied using AFLP fingerprinting. The results show that allopolyploidization could have been involved in the diversification of this group, specifically in species P. langeanum and P. maletii. Molecular data confirm the presence of P. britannicum in the Iberian Peninsula and key steps are provided to identify the species that are morphologically the most challenging.  相似文献   
995.
Virology, genetics and immunology of murine lymphomagenesis   总被引:2,自引:0,他引:2  
  相似文献   
996.
The presence of osteoclast progenitor cells in embryonic, fetal, young growing, and adult murine tissues and organs was investigated in a coculture system with fetal metatarsal bones stripped of periosteum and not yet invaded by osteoclasts. Osteoclasts were found to originate from the early yolk sac and from every tissue tested in the fetus and young mouse. In the adult mouse they were formed only from tissues with a large mononuclear phagocyte population. No osteoclasts could be generated from the young embryo proper, prior to establishment of the vascular connection with the yolk sac. Progenitors of osteoclasts or their stem cells therefore do not develop from undifferentiated mesenchyme outside the yolk sac, but are distributed from the yolk sac to embryonic tissues and hematopoietic organs through the vascular circulation. The embryonic distribution of osteoclast progenitors coincides with the distribution of immature macrophages. Furthermore, they are present before the formation of monocytes in the fetus. The results also indicate that osteoclast precursor cells are not identical with mature, differentiated macrophages, but are cells with little capacity to phagocytose and therefore are, at the most immature progenitors of macrophages or cells of an early diverging lineage. In view of these results the derivation of osteoclasts is discussed.  相似文献   
997.
Mitotic HeLa cells (M cells) synthesize protein at about 25% of the rate of S phase cells. This decrease in protein synthesis is due to a reduction in the rate of initiation. However, extracts prepared from M cells are almost as active in protein synthesis as S cell extracts. Both cell extracts are quite active in in vitro initiation of protein synthesis. Moreover, two steps in initiation, binding of Met-tRNAf to 40S ribosomal subunits and binding of mRNA to ribosomes, show similar activity in both extracts. The difference in protein synthesizing activity observed in vivo is largely eliminated in the preparation of cell-free systems. The ribosomes of M cells contain small mol wt RNA, which inhibits protein synthesis in vitro. This RNA, which has possibly a nuclear origin, may be a cause of the reduction in the rate of protein synthesis in M cells.  相似文献   
998.
999.
A new method for the analysis of NMR data in terms of the solution structure of proteins has been developed. The method consists of two steps: first a systematic search of the conformational space to define the region allowed by the initial set of experimental constraints, and second, the narrowing of this region by the introduction of additional constraints and optional refinement procedures. The search of the conformational space is guided by heuristics to make it computationally feasible. The method is therefore called the heuristic refinement method and is coded in an expert system called PROTEAN. The paper describes the validation of the first step of the method using an artificial NMR data set generated from the known crystal structure of sperm whale carbon monoxymyoglobin. It is shown that the initial search procedure yields a low-resolution structure of the myoglobin molecule, accurately reproducing its main topological features, and that the precision of the structure depends on the quality of the initial data set.  相似文献   
1000.
Carcinoma tissue consists of not only tumor cells but also fibroblasts, endothelial cells or vascular structures, and inflammatory cells forming the supportive tumor stroma. Therefore, the spatial distribution of proteins that promote growth and proliferation in these complex functional units is of high interest. Matrix-assisted laser desorption/ionization imaging mass spectrometry is a newly developed technique that generates spatially resolved profiles of protein signals directly from thin tissue sections. Surface-enhanced laser desorption/ionization mass spectrometry (MS)combined with tissue microdissection allows analysis of defined parts of the tissue with a higher sensitivity and a broader mass range. Nevertheless, both MS-based techniques have a limited spatial resolution. IHC is a technique that allows a resolution down to the subcellular level. However, the detection and measurement of a specific protein expression level is possible only by semiquantitative methods. Moreover, prior knowledge about the identity of the proteins of interest is necessary. In this study, we combined all three techniques to gain highest spatial resolution, sensitivity, and quantitative information. We used frozen tissue from head and neck tumors and chose two exemplary proteins (HNP1–3 and S100A8) to highlight the advantages and disadvantages of each technique. It could be shown that the combination of these three techniques results in congruent but also synergetic data. (J Histochem Cytochem 58:929–937, 2010)  相似文献   
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