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151.
Scrapie is a transmissible disease that results in progressive degeneration of the central nervous system and death. Although scrapie has been studied histopathologically, relatively little is known concerning neurotransmitter alterations. Specific [3H]muscimol binding to whole brain crude synaptic membranes (CSM) from mice clinically affected with scrapie was significantly (p less than 0.01) reduced, to approximately 73% of that of the controls. Of the brain regions examined, binding to only cerebral CSM was significantly (p less than 0.0001) decreased. Scatchard analyses of saturation curves revealed that the high-affinity (KD = 8 +/- 3 nM) site for muscimol was abolished in cerebral CSM from scrapie-infected mice, while the low-affinity site was unaffected. Binding of [3H]flunitrazepam to cerebral CSM was unaffected by scrapie and was stimulated by GABA to the same extent in both scrapie and control mice. These results suggest that scrapie agent 139A in C57BL/6J mice manifests a portion of its CNS pathology via a high-affinity GABA binding site that is unassociated with the benzodiazepine receptor.  相似文献   
152.
The observations that liveMycobacterium leprae after entry into cultured peritoneal macrophages from mice, reduced the EA rosetting macrophages, have been exploited to determine the minimum inhibitory concentration of diamino diphenyl sulphone and rifampicin. Diamino diphenyl sulphone showed a minimum inhibitory concentration of 0.028 μg/ml and rifampicin 0.11μg/ml when given externally. However, there was accumulation of diamino diphenyl sulphone inside the macrophages. At an external concentration of 0.028 μg/ml the concentration inside the macrophage was 0.5μg/ml. The minimum inhibitory concentration for diamino diphenyl sulphone in this assay system is higher by several folds and that for rifampicin is slightly lower, than what is reported earlier with mice foot pad experiments. The minimum inhibitory concentration reported in this assay system is quite close to what is observed forin vitro inhibition ofMycobacterium lufu with both the drugs  相似文献   
153.
Using a specific radioimmunoassay for gonadotropin releasing hormone, the presence of gonadotropin releasing hormone like material in the first trimester human placenta has been demonstrated. The material has been partially characterized using carboxy methyl cellulose chromatography, high pressure gel permeation chromatography and reverse phase C18 high pressure liquid chromatographic analysis. Analysis for bioactivity revealed that placental gonadotropin releasing hormone is much more active than synthetic gonadotropin releasing hormone inin vitro rat pituitary lutinising hormone release assay.In vitro biosynthetic studies using labelled precursors and immunoaffinity chromatography indicated that first trimester human placenta synthesizes gonadotropin releasing hormone like material.  相似文献   
154.
Summary Synaptogenesis has been studied in the electric organ of embryonic Torpedo marmorata by use of two antisera directed against components of synaptic vesicles (anti-SV) and presynaptic plasma membranes (ap-anti-TSM), respectively. The anti-SV serum was previously shown to recognize a proteoglycan specific for synaptic vesicles. The ap-anti-TSM serum was raised to plasma membranes of synaptosomes derived from the electromotor nerve terminals and affinity-purified on electric-organ gangliosides. The vesicular antigen was first detectable at the 81-mm stage of development, which is 1–2 weeks earlier than the formation of morphologically mature presynaptic terminals, but is coincident with a rise in choline acetyltransferase levels and the ability of the electric organ to generate discharges. The gangliosidic antigen recognized by the ap-anti-TSM was first detectable on the ventral electrocyte surface at the 93-mm stage of development. This indicates that specific carbohydrate epitopes, not present on the growth cones, are expressed during maturation of the nerve terminal. The nerve terminal components recognized by these sera arose pari passu with neurite coverage of the ventral surface of the electrocyte, reaching a maximum in the adult. In contrast, postsynaptic aggregates of acetylcholine receptor, rendered visible with rhodamine-labeled -bungarotoxin, arose previous to the presynaptic antigens, reaching a maximum surface density at 110 mm and then declining in the adult.  相似文献   
155.
Summary Immunocytochemistry has been used to study distribution of cell surface transferrin receptors in erythroid, leukemic (K562) cells. The cells were fixed and labelled with monoclonal (OKT-9) anti-transferrin receptor antibodies; the antibody-labelled receptors were then detected by either immunofluoresceinor immunoferritin-antimouse-antibody conjugates. Typically, the immunoferritin labels were distributed diffusely at the non-coated regions of the cell surface as well as concentrated in the clathrincoated pits. To examine further this pattern of distribution, cells were labelled at 0° C and then warmed to 37° C for zero to 30 min prior to fixation. The majority of the immunoferritin labels were initially dispersed in small groups at the non-coated regions of the cell surface (mean = 6 immunoferritin labels/cluster), but larger groups were common subsequent to incubation at 37° C (mean = 13 immunoferritin labels/cluster). However, the size of immunoferritin labels in the coated pits was unchanged (mean = 12 immunoferritin labels/pit). Immunoferritin labels were typical in coated and uncoated vesicles l min after warming to 37° C, but common in endosomes, multivesicular bodies and lysosomes by 30 min. It appears that single cell-surface receptors form large aggregates prior to their concentration in coated pits. Coated vesicles, uncoated vesicles, and endosomal vacuoles may together form the non-lysosomal compartment where the internalized receptors might be dissociated from the ligands (antibodies).  相似文献   
156.
The receptor for urokinase-plasminogen activator   总被引:8,自引:0,他引:8  
Many human cells and cell lines possess a specific receptor that binds urokinase plasminogen activator (uPA) with an affinity of about 10(-10) M. Bound enzyme is not internalized, is slowly dissociated, and retains its enzymatic activity. The amino acid sequence of uPA responsible for receptor binding is located within the first 35 aminoterminal residues, ie, in the growth factor domain. Binding, however, is not competed for by other proteins that contain the growth factor domain (including epidermal growth factor). Cells that produce uPA secrete the pro-uPA form, which subsequently binds to the receptor. A431 cells, in fact, have their receptors completely saturated with pro-uPA. It is proposed that uPA:uPA-receptor interaction plays a direct role in physiological and pathological processes that require cell migration.  相似文献   
157.
The colony-stimulating factor, CSF-1, selectively stimulates the survival, proliferation, and differentiation of mononuclear phagocytes. The solubilization, assay, and characteristics of the CSF-1 receptor from the J774.2 murine macrophage cell line are described. The recovery of cell-surface receptor in the postnuclear supernatant membrane fraction of hypotonically disrupted cells was 76%. Recovery of the ligand binding activity of the receptor after solubilization of this fraction with 1% Triton X-100 was approximately 150%. The binding of 125I-CSF-1 to intact cells and membrane preparations was consistent with the existence of a single class of high-affinity receptor sites. In contrast, the equilibrium binding of 125I-CSF-1 to the solubilized postnuclear fraction indicated the existence of two distinct classes of binding site (apparent Kds 0.15 nM and 10 nM). A rapid assay was developed for the high-affinity sites, which were shown to be associated with the CSF-1 receptor. The function of the low-affinity sites, which have not been demonstrated on intact cells or cell membranes and which are 13 times more abundant than the high-affinity sites, is unknown. The solubilized high-affinity receptor-CSF-1 complex was stable on storage at 0 degrees C and -70 degrees C but dissociated at 37 degrees C. Dissociation also occurred at 0 degrees C in buffers of low pH (4.0) or high ionic strength (0.7 M NaCl).  相似文献   
158.
Epinephrine-promoted release of [3H]guanylylimidodiphosphate ([3H]Gpp(NH)p) from human platelet membranes has been used to probe the interactions between alpha2-adrenergic recpetors and Ni, the guanine nucleotide binding protein that couples those receptors to an inhibition of adenylate cyclase activity. We show here that ADP, which also acts through specific platelet receptors to inhibit adenylate cyclase activity, also promotes the release of [3H]Gpp(NH). The amount of [3H]Gpp(NH)-release elicited by epinephrine and by ADP together is equal to the sum of the amounts released by the two agents acting individually. Furthermore the maximal amounts of [3H]Gpp(NH)-release elicited by each of the two agents approximates the numbers of receptors for ADP and epinephrine present in the platelet membranes. These results suggest that the two receptor types interact with distinct portions of the pool of Ni molecules and that each receptor initiates guanine-nucleotide exchange on a single molecule of Ni.  相似文献   
159.
The function of the syncytiotrophoblast in maternal-fetal exchange is related to the properties of its microvillous (maternal-facing) and basal (fetal-facing) plasma membranes. We have previously reported the properties of the microvillous membrane (Smith, C.H., Nelson, D.M., King, B.F., Donohue, T.M., Ruzycki, S.M. and Kelley, L.K. (1977) Am. J. Obstet. Gynecol. 128, 190–196), and now describe the purification and partial characterization of the basal plasma membrane. Sonication and incubation with EDTA were used to isolate selectively the basal cell membrane. These steps were followed by a more conventional purification by centrifugation. The trophoblast was disrupted and its microvillous membrane and cytoplasmic contents were removed by sonication. The exposed basal cell membrane was selectively released from the underlying basal lamina by sonication in the presence of EDTA and further purified by discontinuous Ficoll gradient centrifugation. The material at the 4–10% Ficoll interface consisted of smooth membrane vesicles with internal microfilaments. It was 45-fold enriched in dihydroalprenolol binding activity and 11-fold enriched in ouabain binding activity. Other enzymatic analyses, including alkaline phosphatase, cytochrome-c oxidase, cytochrome-c reductase and galactosyl transferase indicated low contamination by other organelles. This procedure yields a preparation of relatively high purity which should be suitable for investigation of transport and other functions of the basal surface membrane of trophoblast. In principle, the purification procedures used may be applicable to other transporting epithelia.  相似文献   
160.
Three forms of acetyl coenzyme A: choline-O-acetyltransferase (EC 2.3.1.6, ChAT) have been isolated from mouse and rat forebrain synaptosomes with a 100 mM sodium phosphate (NaP) buffer of pH 7.4, a high-salt solution (500 mM NaCl), and a 2% Triton DN-65 solution, respectively. The Triton-solubilized form of ChAT differed from the other two forms in its capacity to acetylate homocholine, its pH profile, and its sensitivity to denaturation. NaCl-solubilized ChAT could be distinguished from the other two forms with respect to pH profile, sensitivity to inhibition by 4-(1-naphthylvinyl) pyridine (in the presence of Triton), and apparent Km value for choline acetylation. The caudate and putamen of rat brain contained the highest amount of ChAT activity, based on tissue wet weight, and the cerebellum contained the least of the brain regions examined; only the cerebellum had more membrane-bound than soluble ChAT. Septal lesion reduced ChAT activity in the NaP- and Triton-solubilized fractions prepared from hippocampus by 68% and 64%, respectively, whereas it reduced the activity of the NaCl-solubilized fraction by only 21%. These results suggest that three different forms of ChAT may exist in both mouse and rat brain.  相似文献   
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