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111.
Postnatal D2-CAM/N-CAM Sialylation State Is Controlled by a Developmentally Regulated Golgi Sialyltransferase 总被引:2,自引:0,他引:2
Abstract: Golgi-enriched fractions have been isolated from rat brain of increasing postnatal age and defined by electron microscopy and distribution of marker enzymes. The expression of sialyltransferase activity associated with these fractions has been demonstrated to developmentally decrease and this appeared to be, in part, dependent on endogenous competitive inhibition. The developmental regulation of this activity paralleled the sialylation state of the neural cell adhesion molecule (D2-CAM/N-CAM) and could be demonstrated to be capable of endogenously sialylating this protein in the isolated Golgi fractions. In 12-day-old animals the majority of the transferred [14 C]sialic acid was found to be associated with the high-molecular-weight [>200 kilodaltons (kd)] form of D2-CAM/N-CAM, indicative of the protein having been heavily sialylated. Sialylation of the individual D2-CAM/N-CAM polypeptides was also demonstrated in both 12-day and adult animals and transfer was evident only in the 180-kd and 115-kd components and not in the 140-kd component. In contrast, Golgi-enriched fractions prepared from adult animals showed little capability of heavily sialylating D2-CAM/N-CAM to any significant extent. 相似文献
112.
Periphytic communities in running waters were examined as they developed on granite rocks, concrete balls and glass slides. At equivalent cell densities, no differences in pigment concentrations, species diversity or production levels were found among the different substrata examined. Development of the assemblage appeared to result from the elongation of short algal filaments which had initially settled on the surface. As these communities matured, a distinct canopy and understory developed. Cellular metabolisms were comparable among the communities. In the understory of the communities, even though the cellular content of chl a and b did not differ, chl c and carotenoid pigment concentrations were higher than those in the over-story. Bicarbonate assimilation of Tabellaria fenestrata (Lyng.) Külz. and Eunotia pectinalisi var. pectinalis (O. F. Müll?) Rabh. was higher than that of the more abundant Tabellaria flocculosa (Roth.)Kütz. var. flocculosa IV (sensu Koppen) at both high and low cell densities. This probably reflects a seasonal succession of colonizing species. Glucose assimilation appeared to be mainly attributable to bacterial activity, and algal cells of the upper layer were less active than those of the bottom. The small amount of glucose that was incorporated by the algal cells was probably absorbed passively since its amount was in direct proportion to cell volumes. 相似文献
113.
Populations of the vernal cladoceranDaphniopsis ephemeralis are found in woodland ponds throughout southern Ontario. The species reproduces by cyclic parthenogenesis, and genotype frequencies
at allozyme loci are ordinarily in good agreement with Hardy-Weinberg expectations. Occasional heterozygote deficiencies are
apparently the consequence of admixture of ephippial hatchlings produced in temporally separated bouts of sexual reproduction.
Considerable heterogeneity in genotypic frequencies exists among local populations in southwestern Ontario, indicating that
gene flow among populations is restricted. Inbreeding coefficients suggest that populations receive an average of 0.3 migrants
per generation. The completion of a sexual life cycle is made possible despite the brief persistence of populations by the
emergence of males from ephippial eggs and by the production of equal numbers of male and female progeny in the first parthenogenetic
brood. 相似文献
114.
The defence reaction of operculum closing in response to the presence of the molluscivorous leech Glossiphonia complanata (L.) and the non-molluscivorous Erpobdella octoculata (L.) was studied in four species of freshwater prosobranch gastropod. Bithynia tentaculata (L.) and Valvata piscinalis (Müller) can distinguish between the leeches, reacting only to G. complanata. V. piscinalis is capable of a greater degree of distance chemoreception of the leech ‘scent’. Valvata cristata Müller and Potamopyrgus jenkinsi (Smith) did not react to either leech. V. cristata may not be a potential prey item for G. complanata, while P. jenkinsi is fed on by the leech, but is a relative newcomer to the freshwater fauna.
Animal Ecology Research Group, Department of Zoology, University of Oxford
Commonwealth Forestry Institute, Department of Plant Sciences, University of Oxford 相似文献
115.
C R Paul C A Belfi A V Arakali H C Box 《International journal of radiation biology and related studies in physics, chemistry, and medicine》1987,51(1):103-114
The mediation of radiation-induced damage to dinucleoside monophosphate by oxygen and by glutathione was studied. The sequence isomers d(TpA) and d(ApT) were X-irradiated in aqueous solutions and the products isolated by reverse-phase high-performance liquid chromatography. The main products were characterized by proton NMR spectroscopy. In the presence of oxygen the principal products are the formamido derivative formed by breakdown of thymine and the aldehyde derivative formed at the 5' end of the dinucleoside monophosphate, both nucleoside monophosphates and free bases. In the presence of glutathione, the two stereoisomers of the 5,6-dihydrothymine derivatives are prominent. Radiation-induced damage to d(TpA) and d(ApT) in the solid state was also studied. 相似文献
116.
Sequence of the halobacterial glycosaminoglycan 总被引:3,自引:0,他引:3
The cell-surface glycoprotein of halobacterium contains a sulfated repeating unit saccharide chain, similar to the mammalian glycosaminoglycans. The composition of a presumptive repeating pentasaccharide unit of this glycosaminoglycan is 1 GlcNAc, 1 GalNAc, 1 Gal, 1 GalA (where GalA represents galacturonic acid), 1 3-O-methyl-GalA, and 2 SO42-. Linkage to protein of this glycoconjugate involves the hitherto unique unit Asn-GalNAc, with the N-linked asparagine residue being the second NH2-terminal amino acid and part of the common N-linked glycosyl acceptor sequence Asn-X-Thr(Ser). Transfer of the completed, sulfated glycosaminoglycan from its lipid precursor to the protein occurs at the cell surface, and the presence of this sulfated saccharide chain in the cell-surface glycoprotein seems to be required to maintain the structural integrity of the rod-shaped halobacteria. In this paper, we report the complete saccharide structure of this N-linked glycosaminoglycan. This structure is deduced from chemical analyses of fragments that were isolated after hydrazinolysis and subsequent nitrous acid deamination or after mild acidic hydrolysis of purified Pronase-derived glycosaminoglycan-peptides. The halobacterial glycosaminoglycan consists, on the average, of 10 repeating pentasaccharide units of the following structure. (formula: see text) The reducing end N-acetylgalactosamine residue is linked directly to the asparagine, without a special saccharide linker region. 相似文献
117.
Demonstration of up-regulated IL 2 receptor expression on an in vitro cloned BCL1 subline 总被引:1,自引:0,他引:1
K Nakanishi T Hashimoto K Hiroishi K Matsui T Yoshimoto H C Morse J Furuyama T Hamaoka K Higashino W E Paul 《Journal of immunology (Baltimore, Md. : 1950)》1987,138(6):1817-1825
We have established BCL1 CL-3 cells capable of responding to B15-TRF and interleukin 2 (IL 2). This clone has both high affinity and low affinity receptors for IL 2 (IL 2R), but IL 2 by itself did not stimulate either proliferation or immunoglobulin (Ig) secretion. B15-TRF, which possesses both growth and differentiation activity, causes an increase in size of CL-3 cells and renders CL-3 cells responsive to IL 2, including an increased expression of IL 2R (eight-fold to 10-fold) and the differentiation of CL-3 cells into Ig secretion (60 to 80% of cultured cells). CL-3 cells pretreated with B15-TRF for 12 hr become competent to respond to IL 2 by up-regulation of IL 2R within 12 hr. In contrast CL-3 cells pretreated with IL 2 for 12 hr required 24 hr B15-TRF stimulation to result in IL 2R up-regulation. Thus the ordered action of B15-TRF and IL 2 is the most effective operational pathway for the up-regulation of IL 2R. This IL 2-mediated IL 2R up-regulation and induction of Ig synthesis depends upon the concentration of IL 2 in the culture. Both responses seem to be caused by IL 2 molecules bound to high affinity IL 2R. However, the possibility of involvement of low affinity IL 2R can not be vigorously excluded. In fact the level of IL 2 required for a response is far higher than that needed for activated T cell proliferation. This cloned BCL1 subline promises to be a useful tool for studying the regulation and mechanisms of B cell responses. 相似文献
118.
High-efficiency purification and chemical characterization of B cell stimulatory factor-1/interleukin 4 总被引:5,自引:0,他引:5
J Ohara J E Coligan K Zoon W L Maloy W E Paul 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(4):1127-1134
B cell stimulatory factor-1/interleukin 4, a lymphokine produced by phorbol ester activated-EL-4 thymoma cells, was purified to homogeneity in good yield by a two-step purification procedure, using affinity chromatography and a single subsequent round of reverse-phase high-performance liquid chromatography. The N-terminal sequence of the first 24 amino acids was consistent with that inferred from the nucleotide sequence of BSF-1 cDNA clones. Amino acid composition analysis also agreed well with that predicted from the nucleotide sequence. A rabbit antibody to a peptide corresponding to positions 100 to 113 inferred from the nucleotide sequence of the cDNA clones bound to BSF-1 purified from EL-4 cells. Purified BSF-1 possesses complex N-linked glycosidic side chains as shown by reduction in Mr from 20,000 to approximately 15,000 by endoglycosidase F but not by endoglycosidase H treatment. Removal of these N-linked sugars does not diminish the activity of BSF-1 as a costimulant in the response of B cells to anti-IgM. By contrast, the reduction of disulfide bonds completely destroyed biologic activity. A monoclonal antibody to BSF-1 blocks its binding to cellular receptors and inhibits biological activities, whereas antibody to the BSF-1 peptide (100-113) has neither effect. 相似文献
119.
Summary Patch-clamp techniques were used to study a K channel in the cell membrane of MDCK cells. This cell line derives from the kidney of a normal dog, presumably from the distal nephron, a region involved in potassium secretion. The cells were cultured in confluent monolayers and approached from the apical side. The K channel we describe is Ca2+ and voltage activated, has a conductance of 221±7 pS, and can be inhibited by 10mm tetraethylammonium and by 1mm quinidine, but not by 4-aminopyridine, nor by 1mm Ba2+ added to the outer side. Using the whole-cell configuration, we find that most of the cationic conductance of the membrane is constituted by a K-specific one (maximum K conductance 32.1±3.9 nSvs. a leak conductance of 1.01±0.17 nS). Comparisons of the maximum K conductance with that of a single K channel indicates that an MDCK cell has an average of 145 such channels. The membrane capacity is 24.5±1.4 pF. 相似文献
120.
Summary DNA from the kangaroo rat,Dipodomys ordii, contains a 3.3-kb, highly repeated sequence that is interspersed throughout the genome in small tandem clusters. One 3.3-kb unit has been cloned into pBR322 and the nucleotide sequence determined. The clone used was shown to be representative of the bulk of such sequences found in the genomic DNA. The sequence contains 10 homologous subunits each ca. 260 bp in length. Comparison of these to one another yielded a 258-bp consensus sequence containing a 35-bp terminal inverted repeat. Two unique stretches also occur. One of these contains a region that could serve as a promoter for RNA polymerase III; the other contains a sequence related to the ARS sequences of yeast. It is proposed that an ancestral sequence similar to the consensus sequence was amplified to 10 or more units, and that, subsequently, two other sequences were inserted. The properties of these insertions may have led to the dispersal of the sequence throughout the genome. 相似文献