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71.
Bovine t hymic peptide extract (1–100 g/ml) is shown to completely inhibit the binding of [125I]VIP to rat blood mononuclear cells, lymphoid cells of spleen, and liver plasma membranes. In the three models, the bovine thymic peptide extract inhibits [125I]VIP binding with a potency that is 4000–7000 times lower than that of the native VIP, on a weight basis. In rat liver plasma membranes, the bovine thymic peptide extract stimulates adenylate cyclase with a maximal efficiency that is similar to that of VIP. At maximal doses, VIP and thymic peptide extract do not exert an additive effect on adenylate cyclase, suggesting that the activation of the enzyme by the bovine thymic peptide extract occurs through VIP receptors. Finally, no VIP-like immunoreactivity was detected in the thymic peptide extract using an antiserum raised against mammalian VIP. All these data suggest the presence in the bovine thymic peptide extract of a new substance which behaves as a VIP agonist in rat. 相似文献
72.
73.
Receptors for vasoactive intestinal peptide (VIP) have been characterized in rat lymphoid cells. The interaction of [125I] VIP with blood mononuclear cells was rapid, reversible, specific and saturable. At apparent equilibrium, the binding of [125I] VIP was competitively inhibited by native VIP in the 0.01-100 nM range concentration. The binding data were compatible with the existence of two classes of receptors: a high-affinity class with a Kd = 0.050 +/- 0.009 nM and a low binding capacity (2.60 +/- 0.28 fmol/10(6) cells), and a low-affinity class with a Kd = 142 +/- 80 nM and a high binding capacity (1966 +/- 330 fmol/10(6) cells). Secretin, glucagon, insulin and somatostatin did not show any effect at a concentration as high as 100 nM. With spleen lymphoid cells, stoichiometric studies were performed. The binding data were compatible with the existence of two classes of receptors: a high-affinity class with a Kd = 0.100 +/- 0.033 nM and a low binding capacity (4.60 +/- 1.07 fmol/10(6) cells), and low-affinity class with a Kd = 255 +/- 110 nM and high binding capacity (2915 +/- 1160 fmol/10(6) cells). With thymocytes, no binding was obtained under different conditions. 相似文献
74.
Eric D. Green Irving Boime Jacques U. Baenziger 《Molecular and cellular biochemistry》1986,72(1-2):81-100
Luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone from pituitary and chorionic gonadotropin from placenta are a family of glycoproteins, each consisting of an and subunit. Within an animal species, the subunit of all four hormones contains the identical amino acid sequence, while each subunit is distinct and confers biologic specificity to the hormone dimer. Despite sharing common subunits, these hormones bear Asn-linked oligosaccharides which differ in structure. Whereas chorionic gonadotropin contains exclusively neutral and sialylated oligosaccharides, the pituitary hormones bear neutral, sialylated, sulfated, and sialylated/sulfated structures. The sulfated oligosaccharides are unique in structure and are more prevalent on certain pituitary hormones, indicating that the synthesis of these unusual oligosaccharides is tightly regulated. The differences in oligosaccharide structures in conjunction with the highly specific endocrine responses elicited by these hormones, suggest an important functional role for the oligosaccharides, such as metabolic clearance, control of hormone response, modulation of hormone potency, and/or intracellular sorting of hormones into separate secretory granules. 相似文献
75.
Anatoli I. Yashin Kenneth G. Manton Eric Stallard 《Journal of mathematical biology》1986,24(2):119-140
Analyses of human mortality data classified according to cause of death frequently are based on competing risk theory. In particular, the times to death for different causes often are assumed to be independent. In this paper, a competing risk model with a weaker assumption of conditional independence of the times to death, given an assumed stochastic covariate process, is developed and applied to cause specific mortality data from the Framingham Heart Study. The results generated under this conditional independence model are compared with analogous results under the standard marginal independence model. Under the assumption that this conditional independence model is valid, the comparison suggests that the standard model overestimates by 4% the effect on life expectancy at age 30 due to the hypothetical elimination of cancer and by 7% the effect for cardiovascular/cerebrovascular disease. By age 80 the overestimates were 11% for cancer and 16% for heart disease. These results suggest the importance of avoiding the marginal independence assumption when appropriate data are available — especially when focusing on mortality at advanced ages. 相似文献
76.
Summary Mutations in seven different maternal-effect loci on the second chromosome of Drosophila melanogaster all cause alterations in the anterior-posterior pattern of the embryo. Mutations in torso (tor) and trunk (trk) delete the anterior- and posterior-most structures of the embryo. At the same time they shift cellular fates which are normally found in the subterminal regions of the embryo towards the poles. Mutations in vasa (vas), valois (vls), staufen (stau) and tudor (tud) cause two embryonic defects. For one they result in absence of polar plasm, polar granules and pole cells in all eggs produced by mutant females. Secondly, embryos developing inside such eggs show deletions of abdominal segments. In addition, embryos derived from staufen mothers lack anterior head structures, embryos derived from valois mothers frequently fail to cellularize properly. Mutations in exuperantia (exu) cause deletions of anterior head structures, similar to torso, trunk and staufen. However in exu, these head structures are replaced by an inverted posterior end which comprises posterior midgut, proctodeal region, and often malpighian tubules.The effects of all mutations can be traced back to the beginning stages of gastrulation, indicating that the alterations in cellular fates have probably taken place by that time. Analysis of embryos derived from double mutant mothers suggests that these three phenotypic groups of mutants interfere with three different, independent pathways. All three pathways seem to act additively on the system which specifies anterior-posterior cellular fates within the egg. 相似文献
77.
Eric R. Dabbs Renate Hasenbank Berthold Kastner Karl-Heinz Rak Barbara Wartusch Georg Stöffler 《Molecular & general genetics : MGG》1983,192(3):301-308
Summary A battery of immunological tests were used to investigate mutants which had been determined as lacking one or two ribosomal proteins on the basis of two-dimensional polyacrylamide gels. Proteins which were confirmed as missing from the ribosome in one or more mutants were large subunit proteins L1, L15, L19, L24, L27, L28, L30 and L33 and small subunit proteins S1, S9, S17 and S20. Cross-reacting material (CRM) was also absent from the post-ribosomal supernatant except in the case of protein S1. Since mutants lacking protein L11 have been previously described, any one of 13 of the 52 ribosomal proteins can be missing. None of these 13 proteins, except S1, can therefore have an indispensable role in ribosome function or assembly. In several mutants in which a protein was not missing but altered, it was present as several moieties of differing charge and size. 相似文献
78.
A pterosaur vertebral column consisting of the last cervical vertebra, the first five dorsals fused to a notarium, and the following four dorsal vertebrae, is figured and described from the Aptian Santana Formation of the Chapada do Araripe in northeastern Brazil. The specimen is tentatively referred toSantanadactylus brasilensis de Buisonjé. It is the best preserved and most complete pterosaurian notarium known. Its functional significance is discussed. 相似文献
79.
Incorporation of radioactivity from [6-14C]orotate into the pyrimidine constituents of shoots of Pisum sativum, Phaseolus vulgaris and Lathyrus tingitanus was examined with special reference to the unusual pyrimidine constituents. With each species, although 80% of the orotate supplied was catabolized to β-alanine, all the pyrimidine derivatives became radioactively labelled. With Pisum, the major part of the radioactivity incorporated into pyrimidines was located in UMP and the uracil derivatives, including the uracilyl amino acids willardiine and isowillardiine. With Phaseolus, UMP and the uracil derivatives were again the major radioactive products; incorporation of radioactivity into 5-ribosyluracil (pseudouridine), which accumulates in Phaseolus tissues, was comparable to the incorporation into orotidine and twice that found in cytidine. Lathyrus incorporated a substantially larger part of the presented [6-14C] orotate into pyrimidine derivatives than did the other two species. CMP was the most highly radioactive product, followed next by lathyrine and UMP. Surprisingly, 20% of the total radioactivity incorporated into pyrimidines by Lathyrus was located in the pyrimidine amino acid lathyrine. This confirms previous evidence that lathyrine is essentially a product of the orotate pathway. The overall recovery of radioactivity in all three species was 93–95%. The data emphasize the necessity of including the less common pyrimidine constituents, as well as the common ones, in quantitative studies of pyrimidine metabolism in plants. 相似文献
80.