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51.
P S Changelian R M Jack L A Collins D T Fearon 《Journal of immunology (Baltimore, Md. : 1950)》1985,134(3):1851-1858
Phorbol myristate acetate (PMA) has been reported to confer on the C3b receptor (CR1) of neutrophils a capacity for phagocytosis of particles bearing C3b without the involvement of other membrane receptors. In the present study, we employed a monoclonal antibody, YZ-1, that is specific for CR1 to assess the effect of PMA on plasma membrane expression of CR1, total cellular CR1, and internalization of CR1 by neutrophils. PMA had a biphasic effect on the membrane expression of CR1 by purified neutrophils, with 4 ng/ml inducing a 60% increment in receptor expression, and higher concentrations causing up to a 70% decrement. PMA-dependent increases in CR1 expression were not accompanied by corresponding changes in total cellular CR1 and were preempted by treatment of cells with formyl-methionyl-leucyl-phenylalanine (FMLP). PMA-induced decreases in CR1 expression by neutrophils, as measured by binding of indirectly fluoresceinated or radiolabeled YZ-1, or of 125I-labeled dimeric C3b, were maximal with 20 to 30 ng/ml PMA, and occurred within 30 min of incubation at 37 degrees C. The PMA-dependent down-regulation of CR1 by neutrophils was not associated with a comparable decrease in total cellular CR1, and this response was observed to occur also with monocytes but not with peripheral blood lymphocytes. By tagging neutrophil CR1 with 125I-YZ-1 Fab and monitoring accessibility to Protease, intracellular CR1 (inaccessible) was discriminated from receptor on plasma membrane (accessible). Internalization of CR1 occurred within 5 min after addition of PMA to neutrophils, was dose dependent, and involved up to two-thirds of the tagged receptors. Therefore, PMA caused internalization of CR1 by neutrophils in the absence of ligand, indicating that this response was independent of a transmembrane signal generated by a C3b-CR1 interaction. 相似文献
52.
Summary We compared the single-copy DNA sequences of the tetraploid tobacco plant, Nicotiana tabacum, with those of its diploid progenitors N. sylvestris and N. tomentosiformis. We observed that 65% of N. sylvestris and N. tomentosiformis single-copy DNA fragments reacted with each other using moderately stringent hybridization conditions (60° C, 0.18 M Na+). An additional 10% sequence homology was detected when the hybridization temperature was reduced by 10° C. The thermal stability of interspecific single-copy DNA duplexes indicated that they were approximately 6% more mispaired than homologous single-copy DNA duplexes. In contrast, we observed almost no single-copy DNA divergence between N. tabacum and its diploid progenitors. Greater than 99% of N. sylvestris and N. tomentosiformis single-copy DNAs reacted with N. tabacum DNA using moderately stringent hybridization conditions. The thermal stability of these duplexes indicated that they contained no more sequence mismatch than homologous single-copy duplexes. Together, our results show that significant single-copy DNA sequence divergence has occurred between the diploid N. sylvestris and N. tomentosiformis genomes. However, by applying our experimental criteria these single-copy DNAs are indistinguishable from their counterparts in the hybrid N. tabacum nucleus. 相似文献
53.
Summary Filaments formed by the polymerization of RecA protein along DNA in the presence of Mg2+ and adenosine 5-0-(3-thiotriphosphate) (ATPS) are seen by electron microscopy to have a 10 nm diameter with a 9 nm helical repeat. When certain preparations of apparently pure RecA protein are incubated with Mg2+ and ATPS in the absence of nucleic acid for extended times, very long filaments with the same 10 nm diameter and 9 nm axial repeat are seen. We show here that these long 10 nm filaments can contain RNA which is present as a contaminant of the RecA protein and poly(A) which is synthesized during the incubations by an activity that is apparently polynucleotide phosphorylase. RecA protein purified by a procedure developed in this laboratory did not contain RNA and did not form these very long 10 nm filaments. However, when exogenous RNA was added to this protein, 10 nm filament formation was observed. 相似文献
54.
Linda Strause Jack Hegenauer Daniel Burstein Paul Saltman 《Biological trace element research》1985,7(2):75-81
The metabolism of orally administered radiomanganese was studied in mice. Assimilation of absorbed manganese (Mn) was determined using whole body counting techniques. When54MnCl2 was administered, 2.7% of the dose was retained after 10 d compared with 1.2% from the54Mn-nitrilotriacetate (NTA) complex. However, this difference was accounted for by the rapid and persistent adsorption of the Mn onto the teeth of the lower jaw when fed as the ionic salt at pH 2.0 compared with the NTA-chelate fed at pH 9.0. Once corrected for the amount adsorbed onto the teeth, the biodistribution and relative specific activity of the assimilated radiomanganese into a variety of tissues were similar for both forms of the metal. 相似文献
55.
Jack T. Trevors 《Applied microbiology and biotechnology》1985,23(2):152-155
Summary The influence of different O2 concentrations on denitrification was studied in an agricultural soil. In both nitrate and nitrite amended soil, denitrification was not observed until the O2 concentration decreased to 0.20 and 0.21 mol/ml, respectively. Denitrification was not observed in soil samples with O2 concentrations above 0.28 mol/ml in the gas phase. These findings suggest that a completely anoxic environment is not required for denitrification to occur in soil. 相似文献
56.
Dr. Patrick Chardon Marek Kirszenbaum Philippa R. Cullen Claudine Geffrotin Charles Auffray Jack L. Strominger Daniel Cohen Marcel Vaiman 《Immunogenetics》1985,22(4):349-358
Four cDNA probes for the human major histocompatibility complex (MHC) were used to investigate the sheep MHC, in conjunction with serological typing for ovine lymphocyte antigen (OLA). Lymphocytes from a family (two parents and five offspring) of Romanov sheep were subjected to genomic DNA digestion by the restriction endonuclease Eco RI, followed by gel electrophoresis. A single Southern blot representing all seven individuals was then consecutively hybridized with the class I, alpha-DC, beta-DR, and C4 probes, which were originally designed to identify HLA class I, class II (DC and DR), and C4 products, respectively. Using each of the three class I/class II probes, several bands showing DNA polymorphism were detected. The segregation of these bands in the five offspring exactly paralleled the OLA haplotype segregation established by serological typing. A further eight individuals carrying haplotypes which were phenotypically identical to those in the above-mentioned family showed bands in the corresponding positions when tested with the same three probes. Using the C4 probe, no polymorphism was detected in these fifteen individuals.Abbreviations used in this paper MHC
major histocompatibility complex
- OLA
ovine lymphocyte antigen
- kbp
kilobase pair(s)
- MLR
mixed lymphocyte reaction
- RFLP
restriction fragment length polymorphism 相似文献
57.
F.t.-i.r. and laser-Raman spectra of thymine and thymidine in the solid state were recorded. Assignments were proposed for the frequencies observed. The influence of the deoxy sugar on the vibrations of the nucleoside are discussed as a function of its particular puckering. The aim of this work is to elucidate the differences between the molecules constituting the nucleic acids, in order the better to comprehend their biological functions. 相似文献
58.
Operation of the glycolate pathway in isolated bundle sheath (BS) strands of two C4 species was demonstrated from 14C incorporation into two intermediates, glycine and serine, under conditions favourable for photorespiratory activity. Isolated BS strands fixing 14CO2 under light at physiological rates incorporate respectively 3% (Zea mays L., cv. INRA 258) and 7% (Panicum maximum Jacq.) of total 14C fixed into glycine + serine, at low bicarbonate levels (less than the Km for CO2 fixation, 0.8 mM). Higher bicarbonate concentrations depressed the percentage of incorporation into the two amino acids. No labelling was observed in the absence of added glutamate. Oxygen was required for glycine + serine labelling, since 14C incorporation into glycine was largely depressed by argon flushing, and labelling of the two amino acids was nearly suppressed by the addition of the strong reductant, dithionite, especially in maize. Two inhibitors of the glycolate pathway were tested. With α-hydroxypyridine-methanesulfonic acid, an inhibitor of glycolate oxidase, labelling of glycine and serine remained minimal whereas glycolate was accumulated. Isoniazid, an inhibitor of the transformation of glycine to serine induced a 50% increased labelling of glycine in maize BS, and a large decrease in serine labelling. In Panicum, the increase in [14C]-glycine was 90%. These results suggest that the pathway glycolate → glycine → serine operates in these plants. However, leakage of metabolites occurs in BS cells, especially in maize and a large part of newly formed glycolate, glycine and serine is exported out of the cells. Operation of ribulose-1,5-bisphosphate oxygenase activity in competition with ribulose-1,5-bisphosphate carboxylase is demonstrated by the lowering of total 14CO2 fixation when O2 is increased at low bicarbonate concentration. An interesting feature observed in maize BS, at low bicarbonate concentration, was an increase in ribulose-1,5-bisphosphate labelling when the O2 level was decreased. This was accompanied by an increase in CO2 fixation. This could indicate an increased rate in synthesis of ribulose-1,5-bisphosphate (which accumulated) due to a stimulation of ATP synthesis by cyclic photophosphorylation under anaerobic conditions. 相似文献
59.
Based on a tree by tree replacement mechanism, a diffusion model of forest stand canopy composition is formulated and analyzed. The model is used to explore composition dichotomies by estimating coefficients from forest stand data and interpreting the results in terms of mechanisms for succession. The model yields a concrete characterization of the succession phenomenon known as the climax state. 相似文献
60.
We explored O2 flash yield in two cyanophytes, Anacystis nidulans and Agmenellum quadruplicatum. On a rate-measuring electrode, a single flash gave a contour of O2 evolution with a peak at about 10 ms which was maximum (100) for 680 nm background light. On 625 nm illumination the peak was smaller (62) but was followed by an increased tail of O2 attributed to enhancement of the background. After a period of darkness, repetitive flashes (5 Hz) gave a highly damped initial oscillation in individual flash yields which finally reached steady state at 94% of the yield for 680 nm illumination. When O2 of repetitive flashes was measured as an integrated flash yield the results was distinctive and similar to that for a continuous light 1 (680 nm). An apparent inhibition of respiration which persisted into the following dark period was taken as evidence for the Kok effect. With a concentration-measuring electrode, integrated flash yield vs. flash rate showed the same nonlinear behavior as O2 rate vs. intensity of light 1. We draw three conclusions about the two cyanophytes. (a) The plastoquinone pool is substantially reduced in darkness. (b) Because of a high ratio of reaction centers, reaction center 1 / reaction center 2, for the two photoreactions, saturating flashes behave as light 1. (c) Because repetitive flashes are light 1, they also give a Kok effect which must be guarded against in measurements designed to count reaction centers. 相似文献