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101.
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
102.
Lineage-specific expression of c-fos and c-fms in human hematopoietic cells: Discrepancies with the in vitro differentiation of leukemia cells 总被引:2,自引:0,他引:2
Hans Kreipe Heinz J. Radzun Klaus Heidorn Mohammad Reza Parwaresch Bernard Verrier Rolf Müller 《Differentiation; research in biological diversity》1986,33(1):56-60
In vitro differentiation studies using the bipotential human leukemia cell line, HL60, have indicated that high levels of expression of two proto-oncogenes, c-fos and c-fms, are restricted to the myelomonocytic lineage. No such expression has been detected in induced granulocytic cells. In striking contrast to these observations, we found that c-fos mRNA levels are very high in purified human granulocytes, but barely detectable in blood monocytes and tissue macrophages. Human granulocytes contain, however, relatively low levels of c-fos protein, indicating that c-fos mRNA is inefficiently translated or that the protein is rapidly degraded in these cells. In closer agreement with the in vitro results, the level of the expression of c-fms is high in purified blood monocytes and undetectable in granulocytes. We found, however, that the evolution of monocytes into tissue macrophages is accompanied by a significant decrease in c-fms expression, suggesting that the function of c-fms is restricted to specific stages of monocytic differentiation. Our observations also show that results obtained using in vitro differentiation systems have to be regarded with caution, since they may not reflect the in vivo situation. 相似文献
103.
104.
Neurospora crassa mutants deficient in asparagine synthetase 总被引:1,自引:0,他引:1
Neurospora crassa mutants deficient in asparagine synthetase were selected by using the procedure of inositol-less death. Complementation tests among the 100 mutants isolated suggested that their alterations were genetically allelic. Recombination analysis with strain S1007t, an asparagine auxotroph, indicated that the mutations were located near or within the asn gene on linkage group V. In vitro assays with a heterokaryon indicated that the mutation was dominant. Thermal instability of cell extracts from temperature-sensitive strains in an in vitro asparagine synthetase assay determined that the mutations were in the structural gene(s) for asparagine synthetase. 相似文献
105.
Klaus Hallermayer Christine Harmening Herbert Merz Bernd Hamprecht 《Journal of neurochemistry》1983,41(6):1761-1765
The benozomorphan derivative (-)-2-[2-(p-bromoacetamidophenyl)ethyl]-5,9 alpha-dimethyl-2'-hydroxy-6,7-benzomorphan (BAB), capable of reacting with nucleophilic groups, acts on neuroblastoma X glioma hybrid cells as a potent, irreversible opiate agonist. Its potency in inhibiting the increase in cellular cyclic AMP, evoked by prostaglandin E1, is comparable to that of Leu-enkephalin. This also applies to its capacity to compete with [3H]D-Ala2-Met-enkephalinamide ([3H]DAEA) in binding on cell membrane preparations. The comparatively lower potency of (-)-2-[2-(p-acetamidophenyl)-ethyl]-5,9 alpha-dimethly-2'-hydroxy-5,7-benzomorphan (AB), which differs from BAB in the substitution of the bromoacetamido group by an acetamido group, is of the same order of magnitude as that of morphine. The covalent interaction of BAB with the opiate receptors is deduced from the observations that (1) it is not possible to wash away this compound from the receptors, (2) the potency of BAB in inhibiting the specific binding of [3H]DAEA increases with prolonged preincubation time, and (3) AB behaves as a reversible agonist. 相似文献
106.
Germline integration of moloney murine leukemia virus at the Mov13 locus leads to recessive lethal mutation and early embryonic death 总被引:33,自引:0,他引:33
Rudolf Jaenisch Klaus Harbers Angelika Schnieke Jürgen Löhler Ilya Chumakov Detlev Jähner Doris Grotkopp Evelyn Hoffmann 《Cell》1983,32(1):209-216
Thirteen mouse substrains genetically transmitting the exogenous Moloney murine leukemia virus (M-MuLV) at a single locus (Mov locus) have been derived previously. Experiments were performed to investigate whether homozygosity at the Mov loci would be compatible with normal development. Animals heterozygous at an Mov locus were mated, and the genotype of the offspring was analyzed. From parents heterozygous at the loci Mov1 to Mov12, respectively, homozygous offspring were obtained with the expected Mendelian frequency. In contrast, no homozygous offspring or embryos older than day 15 of gestation were obtained from parents heterozygous at the Mov13 locus. When pregnant Mov13 females at day 13 and day 14 of gestation were analyzed, approximately 25% of the embryos were degenerated. Genotyping revealed that these degenerated embryos were invariably homozygous and the normal appearing embryos were either heterozygous or negative for M-MuLV. These results suggest that integration of M-MuLV at the Mov13 locus leads to insertion mutagenesis, resulting in embryonic arrest between day 12 and day 13 of gestation. It is possible that the Mov13 locus represents a gene or gene complex involved in the early embryonic development of the mouse. 相似文献
107.
The effects of intraperitoneally or intracerebrally (DA A-10 area) administered substance P (SP) on locomotor activity of rats were studied in an exact 12-h light/12-h dark cycle changing from dark to light at 6 a.m. SP was administered either at 11 a.m. (light phase, minimal locomotor activity) or at 7 p.m. (dark phase, maximal locomotor activity). The effects of 12.5 micrograms/kg SP intracerebral and 125 micrograms/kg SP intraperitoneal were very similar. In the light phase SP produces excitation but inhibition of locomotion in darkness. Hence, the effect of SP depends on the internal mechanisms controlling motor activity and tends to level off the spontaneous circadian oscillation. We found a long lasting SP effect during both the light and dark period. The present experiments led us to the conclusion that SP has a levelling effect on locomotor activity. Probably this effect might be explained as SP's action on the dopaminergic pathway or dopamine metabolism, because the dopamine content in neurons also has a circadian rhythm. 相似文献
108.
Evidence for dysfunction in the regulation of cytosolic Ca2+ in excitation-contraction uncoupled dysgenic muscle 总被引:6,自引:0,他引:6
In noncontracting, dysgenic murine muscle, excitation is uncoupled from contraction. To test whether the gene lesion is expressed as a defect in the regulation of the intracellular free Ca2+ levels, cultured normal and dysgenic muscle at various stages of development (proliferative myoblasts, early, late, and mature myotubes) were exposed to increasing increments (0.5-mM steps) of extracellular Ca2+ in ionophore A23187-Ca2+-EGTA-buffered media. Normal and dysgenic muscle at all stages (except myoblast) displayed contractures at approximately 500 microM free Ca2+ and higher. Experiments using finer increments of Ca2+ and different ionophore concentrations indicated an external Ca2+ threshold for contracture at 265 microM Ca2+ for early and late myotubes and 47-78 microM for mature normal and dysgenic myotubes. Low extracellular concentrations of calcium (14 microM and 0.76 nM) caused elongation of both normal and dysgenic myotubes. Mature cells were depolarized by exposure to increasing extracellular K+ and monitored by intracellular recording; normal and dysgenic myotubes showed similar reductions in membrane potentials. Depolarization to -35 mV elicited contractures in normal myotubes, but even depolarization to -9 mV in dysgenic cells elicited no response. Thus steady-state depolarization of dysgenic muscle does not cause contractures, which can, however, be elicited by increasing the intracellular free Ca2+. These results offer new evidence for a possible defect in the regulation of Ca2+ levels in dysgenic muscle. 相似文献
109.
Stomatal movement in Zea mays: Shuttle of potassium and chloride between guard cells and subsidiary cells 总被引:2,自引:2,他引:0
Summary When stomates of Zea mays open K and Cl migrate from the subsidiary cells into the guard cells; when the stomates close both elements return to the subsidiary cells. Subsidiary cells function as reservoirs for K and Cl. Import of K and Cl into the guard cells and loss of both elements from the guard cells become observable 1 or 2 min after light is turned on or off, both when histochemical methods and the electron-probe microanalyzer are used for detection. Each stomatal complex of maize contains on the average 10±3×10-13 gram equivalents (eq) of K and 4±1×10-13 eq of Cl. Guard cells accumulate K in the light and CO2-free air at an average rate of 10×10-15 eq K per minute, and Cl at approximately half that rate. 相似文献
110.
Temperature-sensitive initiation of DNA replication in a mutant of Escherichia coli K12 总被引:16,自引:0,他引:16
Detmar Beyersmann Marianne Schlicht Heinz Schuster 《Molecular & general genetics : MGG》1971,111(2):145-158
Summary A mutant of E. coli K12 appears to be temperature-sensitive in the process of initiation of DNA replication. After a temperature shift from 33 to 42°C, the amount of residual DNA synthesis (Fig. 1) and the number of residual cell divisions (Figs. 2,4) indicate that rounds of DNA replication in process are completed, but new rounds cannot be initiated. Following the alignment of chromosomal DNA by amino acid starvation at 33° C no residual DNA synthesis at 42°C takes place (Fig. 5). When the temperature is lowered to 33°C after a period of inhibition at 42°C, the following observations are made: 1. DNA replication resumes and proceeds synchroneously, (Figs. 7, 8a), 2. cells start to divide again only after a lag period of about 1 hour 3. a temporary increase in cell volume is correlated with the frequency of initiation of DNA synthesis (Fig. 8a, b). In a lysogenic mutant strain prophage is inducible; with all bacteriophages tested, replication of phage DNA is not inhibited at 42°C. 相似文献