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81.
Plant secondary compounds can prevent feeding by phytophagous insects or, if ingested, can be poisonous to them. Less attention has been paid to the additional effects they have on feeding behavior when they are only weakly deterrent or not deterrent at all. Experiments were carried out on the generalist grass-hopperSchistocerca americana. Individuals were presented either with two cakes of high-quality artificial food with a single deterrent compound added or with two cakes, each with a different added deterrent compound. The deterrents consisted of single plant secondary compounds that were either marginally or strongly deterrent. There were profound differences in feeding behavior between those individuals given identical and those given different cake types, including longer feeding bouts on single cakes when a choice of different cake types was available. The behavioral effects demonstrate that the presence of secondary compounds in one food can influence the patterns of feeding on other available foods and suggest that such chemicals could impact foraging activities in a complex manner. 相似文献
82.
Single Ca2+ channel records were obtained from plasma membrane-enriched fractions of wheat roots incorporated into artificial planar lipid bilayers. The channel had a unitary conductance of 15 pS for a 10 to 95 mM CaCl2 gradient (cytoplasm: outside of the cell). The voltage dependence displayed by the channel agreed with that expected for Ca2+ channels in the plasma membrane. The channel gating was strongly modified by addition of 20 M extracellular verapamil (a Ca2+ channel antagonist). Extracellular AlCl3 (70 M, pH 4.9) almost completely blocked the channel. 相似文献
83.
Jesús Manuel de la Fuente Amalia Vázquez M. Mar González Miguel Sánchez María Molina César Nombela 《Applied microbiology and biotechnology》1993,38(6):763-769
Thermosensitive mutant strains of Saccharomyces cerevisiae that fail to generate an osmotically stable cell wall when grown at a non-permissive temperature release their cell contents upon expression of the mutation. Therefore, they may represent an alternative for the production of homologous or heterologous protein preparations. In order to analyse the expression of two of these mutations, lyt2 and slt2, we grew the corresponding strains under precisely defined conditions in batch and continuous fermentors. A switch in the temperature of batch cultures from 24° C to 37° C determined lysis of the cells with a significant release of intracellular enzymes. These include alkaline phosphatase and periplasmic proteins such as glucan-degrading enzymes, the pattern of cell lysis and protein release being maintained for about 6 h. One-stage continuous cultures of a lyt2 mutant were maintained for long periods at 37° C; a fraction of the population lysed and released the indicated proteins, but eventually a revertant of the lytic phenotype was selected. To avoid this, a two-stage continuous culture system was developed by connecting two fermentors in series, the effluent from the first one at 24°C being fed to the second one adjusted to 37° C. A steady state of cell lysis and protein liberation was reached in the second-stage fermentor without any evidence of selection of revertants. This system can be very useful for developing conditions for the use of yeast strains to produce protein preparations.
Correspondence to: C. Nombela 相似文献
84.
Miguel Lara-Aparicio Santiago López de Medrano Beatriz Fuentes-Pardo Enrique Moreno-Sáenz 《Bulletin of mathematical biology》1993,55(1):97-110
Based on experimental work on the ontogeny of the electroretinogram circadian rhythm in crayfish, we present a mathematical
model simulating changes in both frequency and amplitude of the electroretinogram oscillation during several developmental
stages until shortly before the adult age. Simultaneously, we propose a hypothetical oscillation in the hormonal release whose
frequency is imposed on the electroretinogram oscillation. The model consists of two coupled nonlinear oscillators in which
a dynamical response is obtained mainly through an Andronov-Hopf bifurcation. Through the construction of the model, a biological
hypothesis about the essential elements underlying the ERG circadian rhythm and their interrelations is formulated and discussed. 相似文献
85.
Honorina Martínez-Blanco Angel Reglero Dr. José M. Luengo 《Journal of industrial microbiology & biotechnology》1994,13(3):144-146
Summary The effect of phenylacetic acid (PAA) and several analogs on the activity of isopenicillin N synthase (IPNS) and acyl-CoA: 6-APA acyltransferase (AT) fromPenicillium chrysogenum Wis 54-1255 has been tested. Whereas the substitution on the ring of a hydrogen atom by hydroxy-, methyl- or methoxy- groups did not cause any effect, the presence of halogens (Cl or Br) at positions 3 and/or 4 of PAA strongly inhibited these two enzymes. The replacement of hydrogen atoms by fluorine in certain positions also caused inhibition, but to a lesser extent. 相似文献
86.
Gavin Sherlock A. Majeed Bahman Amarbirpal Mahal Jia-Ching Shieh Miguel Ferreira John Rosamond 《Molecular genetics and genomics : MGG》1994,245(6):716-723
In the budding yeast Saccharomyces cerevisiae, progress of the cell cycle beyond the major control point in G1 phase, termed START, requires activation of the evolutionarily conserved Cdc28 protein kinase by direct association with GI cyclins. We have used a conditional lethal mutation in CDC28 of S. cerevisiae to clone a functional homologue from the human fungal pathogen Candida albicans. The protein sequence, deduced from the nucleotide sequence, is 79% identical to that of S. cerevisiae Cdc28 and as such is the most closely related protein yet identified. We have also isolated from C. albicans two genes encoding putative G1 cyclins, by their ability to rescue a conditional GI cyclin defect in S. cerevisiae; one of these genes encodes a protein of 697 amino acids and is identical to the product of the previously described CCN1 gene. The second gene codes for a protein of 465 residues, which has significant homology to S. cerevisiae Cln3. These data suggest that the events and regulatory mechanisms operating at START are highly conserved between these two organisms. 相似文献
87.
Phagocytosis has been used to characterize on a functional basis leukocytes adhered to the aortic endothelium of the rat. After intravenous administration of particles, phagocytosis was observed microscopically in esterase-positive leukocytes adhered to the endothelium in whole mounts of aorta. PolybeadR blue and red, 0.5 and 1 μm particle size, were inadequate because they were insufficiently colored to be identified individually at 400. Fluoresbritetm YG 0.25 and 0.50 μm at doses of 0.2 and 2 ± 0.3 m1/100 g, respectively, produced endothelial lesions. The same occurred with Monastral blue BR (MbB) at 0.3 ml/100 g, red iron at 2 ± 16 mg/100 g and India ink at different concentrations depending on the supplier. At lower particle doses, lesions were not found. Deferoxamine mesylate 1.5 mg/100 g intravenous and allopurinol 5 mg/100 g intraperitoneal administered before the particles diminished the number and intensity of lesions. In none of the cases studied was the percentage of phagocytic cells greater than 50%. Clearance curves of MbB and Fluoresbritetm indicated rapid disappearance of particles from the blood. Results indicate that administration of particulate suspensions is not a good method for characterizing the phagocytic leukocytes adhering to the aortic endothelium because low doses produce rapid clearance of particles, thus impeding sufficient leukocyte loading, and higher doses produce endothelial lesions that often impair reliable counting of the adhering leukocytes. 相似文献
88.
Anne M. Donigan R. Christopher Cavalli Angel A. Pena C. Richard Savage Dianne Robert Soprano Kenneth J. Soprano 《Journal of cellular physiology》1993,155(1):164-170
WI-38 cells, density arrested for short periods of time, can be stimulated to re-enter the cell cycle by epidermal growth factor (EGF) alone. However, cells density arrested for longer periods have a prolonged prereplicative phase when serum stimulated and cannot be stimulated by EGF alone. Radio-ligand binding studies performed on WI-38 cells showed that actively growing cells bind [125I]EGF at relatively low levels that increase to a maximum as the cells become contact inhibited. As the cells enter a state of deeper quiescence, EGF binding falls to one-third to one-fifth the short-term growth arrested levels, remaining constant thereafter. The EGF-receptor complexes internalize more slowly in long-term growth arrested cells, and the rate of ligand association to the receptor is lower than short-term growth arrested cells. The amount of EGF receptor protein in lysates of equal numbers of both short- and long-term quiescent cells remains the same. These results suggest that the failure of long-term growth arrested cells to respond to EGF is not due to dramatic changes in the amount of receptor protein during prolonged quiescence but more likely to an alteration in the ability of these receptors to bind ligand and/or activate the EGF signal transduction pathway. © 1993 Wiley-Liss, Inc. 相似文献
89.
Carme Solà Emili Martínez Lluïsa Camón Angel Pazos† Eduard Rodríguez-Farré 《Journal of neurochemistry》1993,60(5):1821-1834
Abstract: The effect of lindane administration on the specific binding of ligands to different sites on the GABAA receptor-ionophore complex was studied in the rat brain by receptor mapping autoradiography. [3 H]Muscimol (Mus), [3 H]flunitrazepam (Flu), and t -[35 S]butylbicyclophosphorothionate (TBPS) were used as specific ligands of GABA, benzodiazepine, and picrotoxinin binding sites, respectively. Rats received a single oral dose of 30 mg/kg lindane and they were classified into two groups according to the absence or presence of convulsions. Vehicle-treated groups acted as controls. The effect of the xenobiotic on ligand binding was measured in different brain areas and nuclei 12 min or 5 h after its administration. Lindane induced a generalized decrease in [35 S]TBPS binding, which was present shortly after dosing. In addition, [3 H]Flu binding was increased in lindane-treated animals, this modification also appearing shortly after administration but diminishing during the studied time. Finally, lindane induced a decrease in [3 H]Mus binding, which became more evident over time. These modifications were observed both in the presence and in the absence of convulsions. However, an increase in [3 H]-Mus binding was detected shortly after lindane-induced convulsions. The observed decrease in [35 S]TBPS binding is in agreement with the postulated action of lindane at the picrotoxinin binding site of the GABAA receptor chloride channel. The effects observed on the binding of [3 H]Flu and [3 H]Mus may be secondary to the action of lindane as an allosteric antagonist of the GABAA receptor. 相似文献
90.
Angel G. Hernandez Ana Rascon Shirley Kutner Henry Roman Zulaika Campos 《Molecular biology reports》1993,18(3):189-195
A correlation between the ratio of the cell surface protease activity to phosphatase activity and the complexity of the pattern of cell surface exposed polypeptides ofLeishmania promastigotes was demonstrated for various strains grown under similar conditions. The ratio of the cell surface protease activity to acid phosphatase activity was high forL. major andL.b. panamensis and it correlates with the expression of a single polypeptide of 63 KDa on their cell surface. Intermediate and lower ratios of these enzymatic activites relate with more complex radio-iodinated patterns: two main bands inL.b. guyanensis (70 and 58 KDa) andL.b. braziliensis (72 and 60 KDa) and three main bands 65, 50, 27 KDa in allL.m. mexicana strains tested. Evidence is presented that the acid phosphatase located on theL.m. mexicana cell surface is not an artifact due to a secondary absorption of the secreted acid phosphatase from the culture medium. These results confirm theLeishmania antigen cell surface heterogeneity. The implications on the biology ofLeishmania and the clinical manifestation of leishmaniasis are discussed. 相似文献