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71.
Cell suspension cultures of the Madagascan Periwinkle Catharanthus roseus (L) G. Don were maintained on Gamborg's B5 medium and their growth monitored by measuring cellular fresh and dry weight, cell number and mitotic activity. Samples of cells of different ages and physiological states were subcultured onto an alkaloid production medium and their rates of growth and alkaloid accumulation measured over a period of 30–45 days. In two experiments the rate of biomass accumulation was directly related to the rate of cellular serpentine accumulation. Possible mechanisms underlying this phenomenon are discussed in relation to the properties of cells comprising the inocula. 相似文献
72.
RNA synthesis was measured in toluenized E. coli by the incorporation of radiolabeled precursor into either acid precipitable or phenol extracted RNA. Exposure to captan (100 microM) caused a 2.6 fold increase in the apparent rate of RNA synthesis. When captan was tested for its effect on the initiation of RNA synthesis, using either rifampicin-treated cells or by measuring the incorporation of gamma [32P]ATP or gamma [32P]GTP, no change was observed in the number of RNA chains being initiated. Thus, captan does not exert its influence at the level of initiation of nascent chains. However, captan did have an effect on chain growth. From calculations of the incorporation of precursors molecules, RNAs isolated from treated cells were measured to be an average of 2.7 times longer than those from untreated cells. RNA chain lengths were also analyzed by polyacrylamide gel electrophoresis. By this latter technique it was also shown that cells exposed to captan synthesized RNAs that were longer than those of untreated cells. Alterations in the degradation of RNA molecules do not account for the captan mediated response in RNA synthesis. 相似文献
73.
Laura Manuelidis 《Human genetics》1985,71(4):288-293
Summary The position and arrangement of individual chromosomes in interphase nuclei were examined in mouse-human cell hybrids by in situ hybridization of biotinylated human DNA probes. Intense and even labeling of human chromosomes with little background was observed when polyethylene glycol and Tween-20 were included in hybridization solutions. Human interphase chromosomes were separated from each other in the nucleus, and were confined to well localized domains. Hybrid cells with a single human chromosome showed a reproducible position of this chromosome in the nucleus. Some chromosomes appeared to have a characteristic folding pattern in interphase. Optical section as well as electron microscopy of labeled regions revealed the presence of 0.2 m wide fibers in each interphase domain, as well as adjacent, locally extended 500 nm fibers. Such fibers are consistent with previously proposed structural models of interphase chromosomes. 相似文献
74.
The catalytic action of dopamine beta-hydroxylase on 1-phenyl-1-propyne results in concomitant loss of enzyme activity. At pH 5.5 and 25 degrees C, 1-phenyl-1-propyne inactivates dopamine beta-hydroxylase in a mechanism-based fashion. The inactivation rate is first-order, follows saturation kinetics, and is strictly dependent on catalysis (oxygen and ascorbate are essential). The inactivation rate of saturating 1-phenyl-1-propyne (kinact) increases from 0.08 to 0.22 min-1 when the oxygen saturation increases from 21 to 100%, respectively. Inactivation also requires a copper-containing catalytically competent enzyme. Tyramine and norepinephrine (respectively, substrate and product of the normal catalytic reaction) protect against inactivation, and no regain of enzyme activity occurs after prolonged dialysis. Experiments with ether-extracted incubation solutions (+/- enzyme) showed no difference in their gas chromatography-mass spectral patterns implying that inactivation of dopamine beta-hydroxylase by 1-phenyl-1-propyne occurs through a kinetic process with a partition ratio (kcat/kinact) equal to or near 1. Thus, this acetylenic substrate analog appears to be a very efficient mechanism-based inhibitor of dopamine beta-hydroxylase. We propose that inactivation of this enzyme by 1-phenyl-1-propyne proceeds by formation of a reactive intermediate that occurs prior to product formation and that alkylates an amino acid residue at the active site of the enzyme. 相似文献
75.
William H. Karasov Edwin Petrossian Laura Rosenberg Jared M. Diamond 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1986,156(4):599-609
Summary What digestive adaptations permit herbivorous nonruminant mammals to sustain much higher metabolic rates than herbivorous lizards, despite gross similarity in digestive anatomy and physiology? We approached this question by comparing four herbivorous species eating the same diet of alfalfa pellets: two lizards (chuckwalla and desert iugana) and two mammals (desert woodrat and laboratory mouse). The mammals had longer small and large intestines, greater intestinal surface area, much higher (by an order of magnitude) food intake normalized to metabolic live mass, and much faster food passage times (a few hours instead of a few days). Among both reptiles and mammals, passage times increase with body size and are longer for herbivores than for carnivores. The herbivorous lizards, despite these much slower passage times, had slightly lower apparent digestive efficiencies than the mammals. At least for chuckwallas, this difference from mammals was not due to differences in body temperature regime. Comparisons of chuckwallas and woodrats in their assimilation of various dietary components showed that the woodrat's main advantage lay in greater assimilation of the dietary fiber fraction. Woodrats achieved greater fiber digestion despite shorter residence time, but possibly because of a larger fermentation chamber, coprophagy, and/or different conditions for microbial fermentation. We conclude with a comparative overview of digestive function in herbivorous lizards and mammals, and with a list of four major unsolved questions. 相似文献
76.
Developmental regulation of 16S acetylcholinesterase and acetylcholine receptors in a mouse muscle cell line 总被引:18,自引:0,他引:18
Nibaldo C. Inestrosa Jeffrey B. Miller Laura Silberstein Lea Ziskind-Conhaim Zach W. Hall 《Experimental cell research》1983,147(2):393-405
We have studied the appearance, distribution and regulation of acetylcholinesterase (AChE) and acetylcholine receptors (AChRs) in a mouse skeletal muscle cell line (C2), that was originally isolated and described by Yaffe & Saxel [54]. In culture, cells from this line form spontaneously contracting myotubes, with overshooting action potentials that are TTX-sensitive. After fusion of myoblasts into myotubes, there was a dramatic increase in the amount of both AChE and AChR. Three forms of AChE, distinguished by their sedimentation on sucrose gradients, were synthesized: 4-6S, 10S, and 16S. The 4-6S and 10S forms appeared 1 day after the cells began to fuse, whereas the 16S form appeared only 2 days after fusion began. Maximal levels of the 16S AChE form (25-30% of the total) were obtained by reducing the concentration of horse serum in the fusion medium. Prevention of myoblast fusion by reducing the calcium levels in the medium decreased the total AChE by 70%, and only the 4-6S form was synthesized. Blocking spontaneous contractile activity of the myotubes by tetrodotoxin (TTX) led to a 50% reduction in all three esterase forms. Thus, the 16S, or endplate form of AChE is not specifically regulated by electrical or contractile activity in the C2 cell line. After fusion the number of AChRs increased rapidly for 3-4 days and then stabilized. Receptor clusters, ranging from 10-30 micron in length, appeared 1 day after myoblast fusion began. When cells were grown in medium containing reduced Ca2+, the total number of AChRs was decreased by 20-50%. Reduction of Ca2+ after myotubes and AChR clusters had formed resulted in dispersal of AChR clusters. Inhibition of muscle contractions with TTX did not affect the number of AChRs or their distribution. 相似文献
77.
Jorge H. Medina María Laura Novas† Eduardo De Robertis† 《Journal of neurochemistry》1983,41(3):703-709
Abstract: This study was designed to analyze possible differences in the binding of [3H]flunitrazepam ([3H]FNZP) and [3H]ethyl - β - carboline - 3 - carboxylate ([3H]β-CCE), to rat brain membranes, in various experimental conditions. In cerebral cortex, hippocampus, cerebellum, and orain stem the number of binding sites for [3H]β-CCE was higher than for [3H]FNZP; both were displaced by clonazepam. Until the 7th day of postnatal brain development the numbers of [3H]FNZP and [3H]β-CCE sites were equivalent; but later on, the β-carboline sites increased to a higher level. Noradrenergic denervation by 6-hydroxydopamine was followed in the hippocampal formation. Already after 2 days, there was a decrease in [3H]FNZP sites, which reached 70% of control after 14 days. Similar results were obtained with DSP-4 denervation. This change was only in Bmax and not in KD, In contrast, the [3H]β-CCE sites did not change with denervation. Neonatal injection of l - 2,4,5 - trihydroxyphenylalamine or DSP-4 produced in the adult a decrease in [3H]FNZP sites in the cerebral cortex, in parallel with the noradrenergic denervation. On the other hand, there was an increase in the cerebellum and brain stem, in correspondence with the hyperinnervation by sprouting. In these rats, the number of sites for [3H]β-CCE did not change in the different brain regions. With 0.1% Triton X-100, applied to synaptosomal membranes, [3H]FNZP binding was reduced by 35%, while that of [3H]β-CCE was not significantly changed. These results suggest that there is heterogeneity of binding sites for benzodiazepine receptors in rat brain. A tentative interpretation of the experiments involving noradrenergic denervation and hyperinnervation, as well as those with Triton X-100, is that [3H]FNZP binds to pre- and postsynaptic receptors, while [3H]β-CCE binds mainly to postsynaptic benzodiazepine receptors. 相似文献
78.
Anna Maria Tagliasacchi Laura Maria Costantina Forino Manuela Frediani Silvana Avanzi 《Protoplasma》1983,115(2-3):95-103
Summary The pattern of DNA and RNA puffs in pair VII of polytene chromosomes has been investigated in the suspensor ofPhaseolus coccineus during early embryo development. The pattern of3H-TdR and3H-U incorporation has been also detected. Collected data indicate that: 1. both heterochromatic regions, p11 and q(111+112), of chromosome pair VII, organize large DNA puffs; 2. DNA puffs of both regions are specific of different embryo differentiation steps; 3. a seasonal influence on the DNA puffing seems also to be present, as demonstrated by the comparison of the results collected in two different crops; 4. the incorporation experiment by3H-TdR evidences that not all DNA puffs show clustered labeling; 5. the RNA puffing of the two regions seems also to be specific of determined embryo stages. 相似文献
79.
Glucosylation of Teichoic Acid: Solubilization and Partial Characterization of the Uridine Diphosphoglucose:Polyglycerolteichoic Acid Glucosyl Transferase from Membranes of Bacillus subtilis 总被引:4,自引:2,他引:2
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Polyglycerolteichoic acid:glucosyl transferase (TAG transferase), one of the three enzymes involved in the pathway leading to the glucosylation of teichoic acid in Bacillus subtilis 168, was investigated. During the early stages of the growth of B. subtilis, TAG transferase is predominantly a soluble enzyme found in the cytoplasm. As growth proceeds, the amount of soluble enzyme decreases and the proportion of insoluble, membrane-bound TAG transferase increases, reaching a maximal value at the close of the logarithmic phase. Data are presented which suggest that these are two forms of the same enzyme, or have some common component. The effects of chaotropic agents, such as sodium trichloroacetate and sodium perchlorate, on the cytoplasmic membrane were also studied. These data show that such compounds can effectively remove the TAG transferase from the membrane in a water-soluble form. A study of some of the physical properties of this solubilized enzyme suggests that there is little difference between the two forms of the enzyme. Experiments are described which indicate that the glucosyl transfer by both the membrane-bound and soluble enzymes is not mediated by lipids. 相似文献
80.
Nature of Escherichia coli B(P1) Yielder Cells at the Time of Infection with Restricted T1 总被引:1,自引:1,他引:0
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In the infection of Escherichia coli B(P1) with restricted T1, it was shown that yielder cells consist of both special and nonspecial cells. Special or predetermined yielders occurred only among the earliest yielders. In most instances, yielder-cell formation was most easily explained by assuming that the first step was a chance escape of the restricted phage DNA from the degrading enzyme of the restricting cell. 相似文献