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991.
Profile of the alpha-bungarotoxin-binding regions on the extracellular part of the alpha-chain of Torpedo californica acetylcholine receptor. 总被引:3,自引:0,他引:3 下载免费PDF全文
The continuous alpha-neurotoxin-binding regions on the extracellular part (residues 1-210) of the alpha-chain of Torpedo californica acetylcholine receptor were localized by reaction of 125I-labelled alpha-bungarotoxin with synthetic overlapping peptides spanning this entire part of the chain. The specificity of the binding was confirmed by inhibition with unlabelled toxin and, for appropriate peptides, with unlabelled anti-(acetylcholine receptor) antibodies. Five toxin-binding regions were localized within residues 1-10, 32-41, 100-115, 122-150 and 182-198. The third, fourth and fifth (and to a lesser extent the first and second) toxin-binding regions overlapped with regions recognized by anti-(acetylcholine receptor) antibodies. The five toxin-binding regions may be distinct sites or, alternatively, different 'faces' in one (or more) sites. 相似文献
992.
993.
J Rivera J M Mullins K Furuichi C Isersky 《Journal of immunology (Baltimore, Md. : 1950)》1986,136(2):623-627
Rat basophilic leukemia (RBL) cells have distinct receptors for IgE and IgG. We assessed the endocytosis of chemically and immunochemically cross-linked mouse-IgG and its influence on the simultaneous endocytosis of IgE. We found that at 37 degrees C, aggregates of IgG and IgE were endocytosed at about the same rate with one-half of the maximal endocytosis occurring in 5 to 13 min, and the efficiency of endocytosis for both ligands ranging from 40 to 70%. We also found that endocytosis of cross-linked IgE and IgG occurred simultaneously and neither ligand significantly affected the rate or extent of endocytosis of the other. The cells accumulated the cross-linked IgG, and then released it to the extracellular environment, at a rate (less than 3%/hr) slower than the released endocytosed IgE (greater than 10%/hr). Using an assay that discriminates between unbound and receptor-bound oligomeric IgG, we found that oligomeric IgG is endocytosed with its receptor, and that the bulk of the ligand remains bound to its receptor for greater than 120 min after endocytosis. The differences in the rate of release of endocytosed IgG vs IgE suggests that the intracellular fate or pathway of these two oligomeric ligands may differ. 相似文献
994.
The procedure for immunochemical adsorption of vesicles with specific antigen on their outer surfaces was improved. When microsomal vesicles were mixed with Staphylococcus aureus cells coated with the antibody against NADPH-cytochrome c reductase, more than 90% of the enzyme activity was adsorbed on the cell, whereas, only about 10% of the activity was adsorbed on cells coated with the same amount of anti-ovalbumin antibody. NADH-cytochrome c reductase and aldehyde dehydrogenase activities were adsorbed on the cell to the same extent as was NADPH-cytochrome c reductase activity. Under this condition, there was no adsorption of the activities of the marker enzymes of lysosomes and Golgi apparatus, whereas large amounts of the activities of the plasma membrane enzymes were adsorbed. The specific activity of NADPH-cytochrome c reductase in the adsorbed vesicles from the microsomal fractions increased considerably. In contrast, marker enzymes of the Golgi or of the plasma membranes could be enriched in unadsorbed vesicles from the Golgi fractions. 相似文献
995.
996.
(1) The antagonistic effect of atropine methyl bromide entrapped in liposomes on contraction of Xenopus intestine in vitro induced by acetylcholine was studied. The results provided some insight into cell-liposome interaction. (2) Acetylcholine (0.1 mM) was added to the medium in the bath (serosal solution), while liposomes containing atropine methyl bromide in their internal and external phases were added on the mucosal side of the intestine. Large multilamellar liposomes were prepared from egg lecithin (phosphatidylcholine, PC) and cholesterol in various molar ratios. Atropine methyl bromide had most effect in liposomes composed of PC and cholesterol in a ratio of 7:3, less in those with a ratio of 4:5, and none in those with a ratio of 9:1. These effects were parallel with the sizes of these liposomes, determined by quasi-elastic light-scattering; that is, the larger the liposomes, the greater was their effect. Addition (to the liposomes) of phosphatidic acid, the negative charge of which increases the distance between the lamellar layers, increased the effect, indicating that atropine methyl bromide in the space between lamellar layers was effective. Another type of liposomes in which atropine methyl bromide was present only in the external phase of liposomes was as effective as liposomes in which atropine methyl bromide was present in both the internal and external phases. (3) From these results the following new model for liposome-mediated stimulation of transport of atropine methyl bromide is proposed. Large multilamellar liposomes have structural defects in their external lamellae through which atropine methyl bromide in the mucosal solution can penetrate into the space between the external lamellar layers and move into intestinal cells through regions of fusion between the outermost layers of the liposomes and the cell membrane. 相似文献
997.
M J Bonete A Manjon F Llorca J L Iborra 《Comparative biochemistry and physiology. B, Comparative biochemistry》1984,78(1):203-206
Acid catheptic activity was measured in crude extracts of muscle, liver, heart, spleen and gonads from the fishes Mujil auratus, Sparus aurata and Lightonatus mormyrus. The spleen was the organ which showed the highest activity. A comparative study of the seven most commonly used extraction methods was made. Some were modified to account for the characteristics of the fish organs and the activity extracted from them. The Siebert method resulted as the best extraction method only if 1 mM EDTA was present in the medium. The activity from Mujil auratus muscle was strongly inhibited by iodoacetate, N-ethylmaleimide, p-hydroxy mercuribenzoate, and diazo-acetyl-DL-norleucine methyl ester. The results indicated the presence of a carboxyl-proteinase and a thiol-proteinase. According to inhibition studies, the levels of proteinase and amidase activities shown by different organs of Mujil auratus were re-examined. The spleen extract showed the maximum activity for both cathepsins, but muscle extract accounted for more than 95% of total catheptic activity. 相似文献
998.
An assay for phenolphthalein in biological fluids has been developed utilizing methods previously applied to the assay of bromosulphalein and to the deconjugation of steroidal compounds in urine. Intestinal perfusate, serum, and urine samples containing phenolphthalein are deproteinized with acidified acetone, the samples dried, and the phenolphthalein redissolved in ethanol. Color is developed with 0.5 m glycine buffer, pH 12, and the samples read at 550 nm after blanking the spectrophotometer with one of the replicates to which acidic glycine buffer is added. To measure conjugated phenolphthalein in urine, the sample is incubated overnight with β-glucuronidase/arylsulphatase prior to phenolphthalein determination as noted above. This method gives an accurate assay of phenolphthalein to 10?5m concentrations with coefficients of variation between 2 and 8% and with no resulting interference from hemoglobin or bilirubin. 相似文献
999.
Inheritance of barley nuclear genes responsible for various morphological marker traits was studied in hybrid populations F2 and Fa. Nine marker genes showed deviation from Mendelian monogenic inheritance depending on the cross direction and maternal cytoplasm. Segregation biases to both recessive mutant and dominant normal phenotypes were observed. Mechanisms of the segregation bias related to cytoplasm substitution in iso- and alloplasmic lines are discussed. 相似文献
1000.
Composition and peptide maps of cross-linked human choriogonadotropin-receptor complexes on porcine granulosa cells 总被引:4,自引:0,他引:4
Radioiodinated human choriogonadotropin was affinity-cross-linked with a cleavable (nondisulfide) homobifunctional reagent to the hormone receptor on porcine granulosa cells and the solubilized sample was electrophoresed. Cross-linked samples revealed four additional bands of slower electrophoretic mobility in addition to the hormone alpha, beta, and alpha beta dimer bands. The four bands corresponded to masses of 68, 74, 102, and 136 kDa whereas the alpha beta dimer band corresponded to 50 kDa. Formation of the four bands requires the 125I-hormone to bind specifically to the receptor with subsequent cross-linking. Binding can be prevented by excess of native hormone but not by follitropin. A monofunctional analog of the cross-linking reagent failed to produce the four bands. They were also produced by cross-linking Triton X-100-solubilized hormone-receptor complexes. Reagent concentration-dependent cross-linking revealed that their formation was sequential; smaller complexes formed first and then larger ones. When gels of the cross-linked sample were treated with reagents that cleave covalent cross-links and then electrophoresed in a second dimension gel, 18-, 24-, 28-, and 34-kDa components were released, in addition to the alpha and beta subunits of the native hormone. Simultaneous peptide mapping of the cross-linked complexes in the gel matrix with Staphylococcus V8 protease or papain revealed progressive proteolysis to generate terminal fragments of 30 or 27 kDa, respectively. These fragments were unique to and commonly present in the 74-, 102-, and 136-kDa hormone-receptor complexes but were not produced by proteolysis of the cross-linked human choriogonadotropin (hCG) alpha beta dimer or the hCG alpha subunit. Apparently, the radioactively labeled segment(s) of the alpha subunit of 125I-hCG was cross-linked to the 24-kDa component. The results demonstrate the protein nature of the receptor and suggest that 125I-hCG was initially cross-linked to the 24-kDa component to generate the 74-kDa complex, then the 28- and 34-kDa components were sequentially cross-linked to the 24-kDa component in the 74-kDa complex to generate the 102- and 134-kDa complexes. 相似文献