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Identification of Glucagon Receptors in Rat Retina 总被引:2,自引:1,他引:1
In this study, we characterize the glucagon receptors on rat retinal particulate preparations. The specific binding of 125I-glucagon was saturable and reversible. Apparent equilibrium conditions were established within 30-45 min. Analysis of binding data is compatible with the existence of two classes of binding sites: a high-affinity class with a KD of 7 +/- 0.8 nM and a Bmax of 2.3 +/- 0.2 pmol/mg of protein and a low-affinity class with a KD of 84.4 +/- 2.5 nM and a Bmax of 16.5 +/- 2.3 pmol/mg of protein. The 125I-glucagon binding to retinal particulate preparation was not inhibited by 1 microM concentrations of insulin, atrial natriuretic factor, angiotensin II, somatostatin, and vasoactive intestinal peptide. However, synthetic human pancreatic growth hormone-releasing factor, hGRF-44, inhibited binding, although the concentration required for half-maximal displacement was 10-fold higher than that for native glucagon. Glucagon binding was GTP sensitive. Inclusion of 0.1 mM GTP in the binding assay produced an increase in the concentration of unlabeled glucagon required for half-maximal displacement of 125I-glucagon, from 23 to 220 nM. Glucagon stimulated adenylate cyclase formation in retinal particulate preparations. The concentration of glucagon required for half-maximal activation of retinal adenylate cyclase was 16.2 nM. These results suggest that glucagon may play a role as a neurosignal transmitter in rat retina. 相似文献
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The importance of litter to nutrient and organic matter storage and the possible influence of species selection on soil fertility
in ten stands each consisting of a separate tree species were examined in this study. The plantations had been grown under
similar conditions in an arboretum in the Luquillo Experimental Forest, Puerto Rico. The species involved were: Anthocephalus chinensis, Eucalyptus × patentinervis, E. saligna, Hernandia sonora, Hibiscus elatus, Khaya nyasica, Pinus caribaea var. hondurensis, P. elliottii var. densa, Swietenia macrophylla, and Terminalia ivorensis. After 26 yr, litter mass ranged from 5 mg ha-1 in the H. sonora stand to 27.2 Mg ha-1 in the P. caribaea stand. Nutrients in the litter (N, P, K, Ca, and Mg) also varied widely, but stands were ranked in different order when ranked
by nutrients in the litter than then ranked according to accumulation of mass. Only E. saligna and A. chinensis stands were ranked similarly in accumulation of both nutrients and mass, and the stand of H. elatus was ranked higher with respect to nutrient accumulation than to accumulation of mass. The nutrient concentration in standing
leaf litter generally increased in the order of recently fallen <old intact< fragmented. Nutrient concentration of standing
leaf litter appears to increase with age and depth in the litter layer. The amount of nutrients stored in the litter compartment
of these plantations was in the same order of magnitude as the quantity of available nutrients in the top 10-cm of mineral
soil. Total litter mass was negatively correlated with the mass-weighted concentration of N, K, and Mg. The same relationship
was found for Ca in the leaf litter and N in the fine wood litter compartments. In some stands (notably P. caribaea, P. elliottii, and E. saligna), leaf litter derived from species other than the species planted in that particular stand had higher nutrient concentration
than leaf litter from the planted species. Soils of the 10 stands were classified in the same soil series and had similar
texture (clay soils). However, significantly different chemical characteristics were found. Results obtained by analysis of
covariance and by limiting comparisons to adjacent stands with similar soil texture, indicate that different species have
had different influences on the concentration of available nutrients in soil. 相似文献
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M D Perez L Sanchez P Aranda J M Ena R Oria M Calvo 《Biochimica et biophysica acta》1992,1123(2):151-155
The interaction of bovine beta-lactoglobulin with palmitic and oleic acids has been studied by a partition equilibrium method. Bovine beta-lactoglobulin displays only one high affinity binding site for fatty acids whose association constants for palmitic and oleic acids are 4.2 x 10(6) and 2.3 x 10(6) M-1, respectively. However, other binding sites with low affinity are also present. The existence of one high affinity binding site is in accordance with the amount of fatty acids naturally bound to beta-lactoglobulin isolated from milk. The effect of beta-lactoglobulin on ruminant pregastric lipases from a pharyngeal extract has been assayed. The activity of pharyngeal lipase on a triglyceride emulsion is increased about 200%, 250% and 190% in the presence of 10 mg/ml, 20 mg/ml and 40 mg/ml of beta-lactoglobulin, respectively, the last concentration representing that found physiologically in colostrum. Albumin, another ligand-binding protein, increases the activity of this enzyme to a lesser extent and high levels tend to inhibit enzyme action. These results indicate that beta-lactoglobulin could participate in the digestion of milk lipids during the neonatal period by enhancing the activity of pregastric lipase through removal of the fatty acids that inhibit this enzyme. 相似文献
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肾综合征出血热(HFRS)为一组抗原性密切相关的布尼亚科汉坦病毒引起的急性传染病。在我国存在至少两种临床表现、动物宿主及流行特征截然不同的血清型别,即血清Ⅰ型(汉坦型)和血清Ⅱ型(汉城型)。这两型病毒间的血清学定型已有报道。近年来,除啮齿类动物外,从临床病人以及非啮齿类动物体内也分离到了HFRS病毒。同时出现两类型别毒株共存,以及从家鼠体内分离到野鼠型毒株或从野鼠体内分离到家鼠型毒株的复杂情形。为此,准确检定并鉴别不同来源毒株型别,将为深入了解其病原学、流行病学以及制定疫苗生产策略提供重要信息。 相似文献
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J. Martin Sanchez F. Ruiz Martinez J. M. Salinas Martinez de Lecea C. Sanchez Rabasco C. Acedo Sanchez M. C. Sanchiz Marin V. Delgado Florencio F. Morillas Marquez 《Systematic parasitology》1996,33(3):177-182
This study presents the results of the characterisation of 17 strains ofLeishmania by isoenzyme electrophoresis from a focus of leishmaniasis in southern Spain: two from human visceral leishmaniasis, four from human cutaneous leishmaniasis and 11 from sandflies. The 17 strains are grouped in 6 zymodemes characterised by their variability as regards to the electrophoretic mobility of the enzymes MDH, G6PD, NP and ME. Thus, we confirm the high intraspecific variability ofLeishmania (L.) infantum in a focus of southern Spain, as already suggested by previous studies. Zymodemes GR-15 and GR-17 are also described for the first time in Spain, and they characteristically possess the same relative electrophoretic mobility in the enzyme ME (93). Sixteen zymodemes of theL. infantum complex found in southern Spain were numerically analysed on the basis of the enzymatic profiles of 122Leishmania strains characterised from this area. 相似文献
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