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11.
Carol Anelli Sheppard Marcia J. Loeb 《Archives of insect biochemistry and physiology》1992,21(3):179-193
A subcellular fraction enriched in plasma membranes was obtained from gypsy moth (Lymantria dispar) larval midgut tissue. Using [45Ca]2+ as a tracer, Ca2+ transport activity by membrane vesicles in the enriched fraction was measured and shown to be ATP-dependent, with a very high affinity for Ca2+ (apparent Km for [Ca2+ free] 1 Abbreviations used: [Ca2+free] = concentration of free (unbound) calcium ion;CaM = calmodulin; F = fraction; IOV = inside-out membrane vesicles; W-5 = N-(6-aminohexyl)-1-naphthalenesulfonamide; W-7 = N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide. = 22 nM). Ca2+ transport was abolished upon addition of the calcium ionophore, A23187. Ca2+-stimulated, Mg2+-dependent ATPase activity peaked between 100 and 200 nM Ca2+free. Ca2+-Mg2+-ATPase activity was inhibited by vanadate, 2 phenothiazine drugs (trifluoperazine and chlorpromazine), and the naphthalene sulfonamide, W-7; the related compound, W-5, and ouabain had a negligible effect. These results suggest the presence of a high affinity plasma membrane Ca2+ pump in gypsy moth larval midgut cells and are discussed in light of earlier work involving calcium transport in isolated midguts of larval Hyalophora cecropia. Ionic and other conditions that characterize the midgut physiology of larval Lepidoptera (e.g., luminal pH; electrochemical gradient for Ca2+; effect of certain ions and inhibitors on Ca2+ transport) contrast significantly with those found in adult Diptera. The implications that these differences may have for calcium regulation are discussed. © 1992 Wiley-Liss, Inc. 相似文献
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The association of thymidine kinase activity and thymidine transport in Escherichia coli 总被引:1,自引:0,他引:1
We have constructed a series of mutants within the putative nucleoside-binding site of the herpes simplex type-1 virus (HSV-1) thymidine kinase (TK)-encoding gene (tk), contained within an expression vector. While most mutations within this sequence produce an inactive protein, we find no absolute requirement for the wild-type Ile166 and Ala167. The uptake of thymidine (dT) into Escherichia coli tdk-, lacking functional endogenous TK activity, is proportional to the amount of TK activity expressed from the heterologous HSV-1 tk gene. In contrast, there is no enhancement in deoxycytidine uptake into E. coli producing (HSV-1) TK. These results imply a specific role for TK in the active transport of dT into E. coli. 相似文献
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The forces required to remove living, fully attached barnacles from the surface of a number of polymeric solids were measured. The forces were related to the surface energy components of the materials. The results indicate a positive correlation between polymer surface energy and force required for barnacle removal. The nonpolar component of the surface energy was more closely related to the removal force than the polar component, although the polar component is significant. Adherence to some composite materials was greater than was consistent with the correlation for noncomposites. 相似文献
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On the fidelity of DNA replication. Lack of primer position effect on the fidelity of mammalian DNA polymerases 总被引:6,自引:0,他引:6
Mechanisms for the fidelity of DNA replication in eucaryotes are not adequately understood. Certain hypotheses can be tested by examining whether the first nucleotide inserted is incorporated with a significantly higher error rate than subsequent nucleotides. Using synthetic oligodeoxynucleotides, we have measured the effect of primer position on single-base misinsertion frequencies at an amber site in phi X174 DNA. Our results show a lack of position effect, indicating that processivity and the most direct "energy relay" proofreading mechanisms are not important determinants in eucaryotic replication fidelity. 相似文献
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Methylation of transfer RNA during transformation of human lymphocytes by phytohemagglutinin 总被引:1,自引:0,他引:1
Methylation of transfer RNA during phytohemagglutinin induced transformation of human lymphocytes was studied by labeling the tRNA with (methyl-H3)-methionine and measuring the distribution of tritium in the methylated nucleotides. An alteration in the pattern of methylation occurred within hours after PHA-stimulation and this change was maintained through several cell generations. There was a 50 to 94% increase in the relative amount of methylated N2-methyl-guanine (1 to 3 hr) and a 40 to 59% decrease in the relative amount of 1-methyladenine (1 to 12 hr). Treatment of the stimulated cells with Actinomycin D prevented the subsequent methylation not tRNA. However, inhibition of protein synthesis by puromycin did not effect the early changes observed in the methylation of tRNA. 相似文献
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Plasmid origin of replication of herpesvirus papio: DNA sequence and enhancer function. 总被引:4,自引:2,他引:2
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D D Loeb N S Sung R L Pesano C J Sexton C Hutchison rd J S Pagano 《Journal of virology》1990,64(6):2876-2883
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