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31.
Else K. Hoffmann Ian H. Lambert Lars Ole Simonsen 《The Journal of membrane biology》1986,91(3):227-244
Summary The net loss of KCl observed in Ehrlich ascites cells during regulatory volume decrease (RVD) following hypotonic exposure involves activation of separate conductive K+ and Cl– transport pathways. RVD is accelerated when a parallel K+ transport pathway is provided by addition of gramicidin, indicating that the K+ conductance is rate limiting. Addition of ionophore A23187 plus Ca2+ also activates separate K+ and Cl– transport pathways, resulting in a hyperpolarization of the cell membrane. A calculation shows that the K+ and Cl– conductance is increased 14-and 10-fold, respectively. Gramicidin fails to accelerate the A23187-induced cell shrinkage, indicating that the Cl– conductance is rate limiting. An A23187-induced activation of42K and36Cl tracer fluxes is directly demonstrated. RVD and the A23187-induced cell shrinkage both are: (i) inhibited by quinine which blocks the Ca2+-activated K+ channel. (ii) unaffected by substitution of NO
3
–
or SCN– for Cl–, and (iii) inhibited by the anti-calmodulin drug pimozide. When the K+ channel is blocked by quinine but bypassed by addition of gramicidin, the rate of cell shrinkage can be used to monitor the Cl– conductance. The Cl– conductance is increased about 60-fold during RVD. The volume-induced activation of the Cl– transport pathway is transient, with inactivation within about 10 min. The activation induced by ionophore A23187 in Ca2+-free media (probably by release of Ca2+ from internal stores) is also transient, whereas the activation is persistent in Ca2+-containing media. In the latter case, addition of excess EGTA is followed by inactivation of the Cl– transport pathway. These findings suggest that a transient increase in free cytosolic Ca2+ may account for the transient activation of the Cl– transport pathway. The activated anion transport pathway is unselective, carrying both Cl–, Br–, NO
3
–
, and SCN–. The anti-calmodulin drug pimozide blocks the volume- or A23187-induced Cl– transport pathway and also blocks the activation of the K+ transport pathway. This is demonstrated directly by42K flux experiments and indirectly in media where the dominating anion (SCN–) has a high ground permeability. A comparison of the A23187-induced K+ conductance estimated from42K flux measurements at high external K+, and from net K– flux measurements suggests single-file behavior of the Ca2+-activated K+ channel. The number of Ca2+-activated K+ channels is estimated at about 100 per cell. 相似文献
32.
Lars Werdelin John A. Long 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1986,19(2):161-169
A set of 18 measurements of the dermal armour of Bothriolepis canadensis Whiteaves (Placodermi, Anti-archa) is analysed with respect to allometric growth patterns. The strongest allometric patterns were found for the orbital fenestra and premedian plate of the head-shield. and the anterior median dorsal plate of the trunk-shield. These are all areas of the greatest importance in antiarch phylogeny and imply a role for ontogenetic effects such as paedomorphosis in the evolution of antiarchs. It is suggested that this is partly a result of the severe constraints on growth in a closed box such as the armour of placoderms, and may be generally true of such arrangements. 相似文献
33.
Brain Cell Biology - Cytochemical techniques were used to study the localization of 5′-nucleotidase in the enteric ganglia and in smooth muscle cells of the guinea-pig ileum, iris and vas... 相似文献
34.
Lars Olof Björn 《Physiologia plantarum》1984,60(3):369-372
Experiments by several authors on the effects of polarized light on phytochromemediated responses in fern gametophytes and in the green alga Mougeotia have earlier been interpreted as showing that the transition moment of phytochrome in the Pr form is parallel to the plasmalemma, but perpendicular to the plasmalemma for the Pfr form of phytochrome. It is now shown that the experimental results can be interpreted differently, and that they are also consistent with a chromophore rotation of about 30° (instead of 90°), as found for immobilized phytochrome molecules in vitro. Thus there is no evidence for a rotation of the whole phytochrome protein. For the gametophyte of Adiantum it is calculated that the Pr transition moment is inclined 17° to the plasmalemma, and the Pfr transition moment ca 50°, corresponding to an in vivo chromophore rotation of ca 33°; however, these values are very approximate. 相似文献
35.
Conidiation in Alternaria cichorii Nattras is reversibly stimulated by near ultraviolet radiation (NUV, ca 313 nm) and inhibited by blue light (ca 450 nm) and seems to be a mycochrome-mediated process. After induction with plane-polarized NUV, blue light polarized perpendicularly to the NUV was more effective in counteracting the induction than was blue light polarized parallel to the NUV. From this the conclusions are drawn that (a) both the blue-absorbing component (presumably a flavo-protein) and the PNUV of the mycochrome system are membrane-bound and that (b) the transition moment associated with blue light absorption in the presumed flavoprotein forms an angle of at least 53° with the transition moment associated with NUV absorption in PNUV . 相似文献
36.
Elisabet Johansson Lars Hedbys Per-Olof Larsson Klaus Mosbach Alf Gunnarsson Sigfrid Svensson 《Biotechnology letters》1986,8(6):421-424
Summary Three naturally occurring isomers of the disaccharideO--d-mannosyl-d-mannoside were synthesized by reversing the hydrolytic activity of jack bean -mannosidase at 75°C in a very high concentration of mannose. Higher oligosaccharides were also obtained at the later stages of the reaction. The maximum total yield of disaccharides was 37% (w/w) based on the total amount of saccharides. 相似文献
37.
Steen Kølvraa Torben A. Kruse P. K. A. Jensen Kirsten H. Linde Søren R. Vestergaard Lars Bolund 《Human genetics》1986,74(3):284-287
Summary EDA (ectodermal dysplasia, anhidrotic) is an X-linked recessive disorder characterized by hypohidrosis, hypoor anodontia, and hypotrichosis. A possible linkage between the gene for EDA and a number of restriction fragment length polymorphisms (RFLPs) spread over the X chromosome was investigated in two Danish families segregating EDA. No recombination between the gene for EDA and our probe pTAK8, which detects a two allele polymorphism in the region Xp11-q12, was found in nine informative meiotic events (seven of which are phase known), giving a maximal lod score of 2.41 at a recombination fraction of 0.00. This juxtacentromeric location of the gene for EDA agrees well with the linkage data obtained with the other markers used in this study. 相似文献
38.
Na+, Cl− cotransport in Ehrlich ascites tumor cells activated during volume regulation (regulatory volume increase) 总被引:2,自引:0,他引:2
Else K. Hoffmann Carsten Sjøholm Lars Ole Simonsen 《The Journal of membrane biology》1983,76(3):269-280
Ehrlich ascites cells were preincubated in hypotonic medium with subsequent restoration of tonicity. After the initial osmotic shrinkage the cells recovered their volume within 5 min with an associated KCl uptake. The volume recovery was inhibited when NO-3 was substituted for Cl-, and when Na+ was replaced by K+, or by choline (at 5 mM external K+). The volume recovery was strongly inhibited by furosemide and bumetanide, but essentially unaffected by DIDS. The net uptake of Cl- was much larger than the value predicted from the conductive Cl- permeability. The undirectional 36Cl flux, which was insensitive to bumetanide under steady-state conditions, was substantially increased during regulatory volume increase, and showed a large bumetanide-sensitive component. During volume recovery the Cl- flux ratio (influx/efflux) for the bumetanide-sensitive component was estimated at 1.85, compatible with a coupled uptake of Na+ and Cl-, or with an uptake via a K+,Na+,2Cl- cotransport system. The latter possibility is unlikely, however, because a net uptake of KCl was found even at low external K+, and because no K+ uptake was found in ouabain-poisoned cells. In the presence of ouabain a bumetanide-sensitive uptake during volume recovery of Na+ and Cl- in nearly equimolar amounts was demonstrated. It is proposed that the primary process during the regulatory volume increase is an activation of an otherwise quiescent, bumetanide-sensitive Na+,Cl- cotransport system with subsequent replacement of Na+ by K+ via the Na+/K+ pump, stimulated by the Na+ influx through the Na+,Cl- cotransport system. 相似文献
39.
Rapidly phosphorylated nuclear proteins were investigated in explanted salivary gland cells of Chironomus tentans after labeling with 32Pi. After sonication nuclei were fractionated by centrifugation at 18,000 g into sedimentable (80% of 32P) and not sedimentable (supernatant) material. About 90% of 32P in the supernatant fraction was sedimentable at 100,000 g (disperse chromatin). The disperse chromatin contained 20%–40% of the total nuclear DNA but only 5%–20% of 32P. The 32P-labeled phosphoproteins in the material pelleted at 20,000 g were further fractionated by differential solubility in lysis buffer. Electrophoretic analyses on SDS polyacrylamide gels resolved the 32P-labeled nuclear proteins into 12 major bands in the Mr range of 12,000–120,000. The incorporation of 32P into most bands reached a steady-state within 5–10 min of incubation with 32Pi and was not measurably influenced by cycloheximide, an inhibitor of protein synthesis. The phosphate groups are linked to polypeptide chains by bonds vulnerable to pronase and alkaline phosphatase. All major bands in the pelleted chromatin were also present in the disperse chromatin except for an Mr 95,000 phosphoprotein. Two of the fastest moving 32P-bands comigrated with the core histones H2A and H4. Both possessed a high pI value and were insoluble in 0.35 M NaCl. The H2A-like protein was partially soluble in lysis buffer while the H4-like one was not. The two fast moving 32P-labeled bands with rapidly turned over phosphates may be fractions or variants of the core histones H2A and H4. 相似文献
40.
Factors Affecting Competence for Transformation in Staphylococcus aureus 总被引:22,自引:14,他引:8 下载免费PDF全文
Lars Rudin Jan-Eric Sjstrm Martin Lindberg Lennart Philipson 《Journal of bacteriology》1974,118(1):155-164
A chemically defined medium has been developed for isolation of amino acid-requiring mutants of Staphylococcus aureus strain 8325, and for use as a selective medium in transformation assays. Variables affecting transformation of both plasmid and chromosomal markers have been studied. The optimal pH and temperature for transformation are 6.75 to 7.0 and 30 C, respectively. Ca ions are required for transformation, and only cells lysogenic for the phage phi11 can be transformed. Superinfection of competent cells with phi11 does not increase the transformation frequency. Maximal number of transformants is obtained after 20 min of contact between cells and deoxyribonucleic acid. The transformation frequencies for the plasmid marker erythromycin resistance (ero) and the chromosomal markers trp, thy, and cyt are of the same order of magnitude, whereas the frequency for the chromosomal marker tyr is approximately one order of magnitude lower. 相似文献