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981.
I. W. Althaus J. J. Chou A. J. Gonzales R. J. LeMay M. R. Deibel K. -C. Chou F. J. Kezdy D. L. Romero R. C. Thomas P. A. Aristoff W. G. Tarpley F. Reusser 《Cellular and molecular life sciences : CMLS》1994,50(1):23-28
The tetramer of ethylenesulfonic acid (U-9843) is a potent inhibitor of HIV-1 RT* and possesses excellent antiviral activity at nontoxic doses in HIV-1 infected lymphocytes grown in tissue culture. Kinetic studies of the HIV-1 RT-catalyzed RNA-directed DNA polymerase activity were carried out in order to determine if the inhibitor interacts with the template: primer or the deoxyribonucleotide triphosphate (dNTP) binding sites of the polymerase. Michaelis-Menten kinetics, which are based on the establishment of a rapid equilibrium between the enzyme and its substrates, proved inadequate for the analysis of the experimental data. The data were thus analyzed using steady-state Briggs-Haldane kinetics assuming that the template:primer binds to the enzyme first, followed by the binding of the dNTP and that the polymerase is a processive enzyme. Based on these assumptions, a velocity equation was derived which allows the calculation of all the specific forward and backward rate constants for the reactions occurring between the enzyme, its substrates and the inhibitor. The calculated rate constants are in agreement with this model and the results indicated that U-9843 acts as a noncompetitive inhibitor with respect to both the template:primer and dNTP binding sites. Hence, U-9843 exhibits the same binding affinity for the free enzyme as for the enzyme-substrate complexes and must inhibit the RT polymerase by interacting with a site distinct from the substrate binding sites. Thus, U-9843 appears to impair an event occurring after the formation of the enzyme-substrate complexes, which involves either an event leading up to the formation of the phosphoester bond, the formation of the ester bond itself or translocation of the enzyme relative to its template:primer following the formation of the ester bond. 相似文献
982.
Evolution and ecological correlates of uniparental reproduction in freshwater snails 总被引:1,自引:0,他引:1
S. G. Johnson C. M. Lively S. J. Schrag 《Cellular and molecular life sciences : CMLS》1995,51(5):498-509
We review the spatial and temporal correlates of uniparental reproduction in freshwater snails as they pertain to the ecological hypotheses for the maintenance of biparental sex. The biogeographic evidence from two species (Potamopyrgus antipodarum andBulinus truncatus) presently supports the Red Queen hypothesis that biparental reproduction is selected as a way to reduce the risk to progeny of parasite attack. Uniparental reproduction in these species is associated with low levels of infection by parasites (castrating digenetic trematodes), suggesting that parthenogenesis or self-fertilization can replace cross-fertilization when the risk of infection is low. In addition, inB. truncatus, the opportunity for cross-fertilization coincides with the season in which parasite attack is highest. In a third species (Campeloma decisum), parthenogenetic reproduction is correlated with latitude and the presence of a non-castrating trematode that may prevent cross-fertilization; these patterns suggest that parthenogenesis has been selected as a mechanism to assure reproduction. Finally, we discuss the spotty taxonomic distribution of parthenogenetic species. 相似文献
983.
984.
E. Bonilla M. Salazar J. Estevez H. Hernández P. Rangel 《Cellular and molecular life sciences : CMLS》1984,40(8):868-869
Summary After i.p. inoculation with the Guajira strain of Venezuelan equine encephalomyelitis virus a significant decrease in the density of (3H) spiroperidol binding sites in the striatum, midbrain and frontal cortex was observed. No changes in the affinity of the receptors could be demonstrated. This finding is compatible with neuronal degeneration caused by the viral infection.Acknowledgments. This work was partially supported by Condes-Luz and Fundacite-Zulia. Butaclamol isomers were a gift of Ayerst Laboratories, Montreal, Canada. 相似文献
985.
Comparative distribution of vasoactive intestinal polypeptide (VIP), substance P and PHI in the enteric sphincters of the cat 总被引:2,自引:0,他引:2
G P McGregor A E Bishop M A Blank N D Christofides Y Yiangou J M Polak S R Bloom 《Experientia》1984,40(5):469-471
In the feline gastrointestinal tract, the neuropeptides, substance P, VIP and PHI were investigated by specific radioimmunoassays and immunocytochemistry. The concentrations of all 3 peptides and the level of peptidergic innervation were significantly less in the anal sphincter than elsewhere, whereas no significant differences were seen between other sphincter and non-sphincter regions. 相似文献
986.
987.
J. -L. Clement 《Cellular and molecular life sciences : CMLS》1984,40(3):283-285
Summary It was possible to separate species and complexes of species in theReticulitermes genus of Western Europe using esterase 3 and acid phosphatase 2. 相似文献
988.
Human hepatitis B vaccine from recombinant yeast 总被引:22,自引:0,他引:22
W J McAleer E B Buynak R Z Maigetter D E Wampler W J Miller M R Hilleman 《Nature》1984,307(5947):178-180
The worldwide importance of human hepatitis B virus infection and the toll it takes in chronic liver disease, cirrhosis and hepatocarcinoma, make it imperative that a vaccine be developed for worldwide application. Human hepatitis B vaccines are presently prepared using hepatitis B surface antigen (HBsAg) that is purified from the plasma of human carriers of hepatitis B virus infection. The preparation of hepatitis B vaccine from a human source is restricted by the available supply of infected human plasma and by the need to apply stringent processes that purify the antigen and render it free of infectious hepatitis B virus and other possible living agents that might be present in the plasma. Joint efforts between our laboratories and those of Drs W. Rutter and B. Hall led to the preparation of vectors carrying the DNA sequence for HBsAg and antigen expression in the yeast Saccharomyces cerevisiae. Here we describe the development of hepatitis B vaccine of yeast cell origin. HBsAg of subtype adw was produced in recombinant yeast cell culture, and the purified antigen in alum formulation stimulated production of antibody in mice, grivet monkeys and chimpanzees. Vaccinated chimpanzees were totally protected when challenged intravenously with either homologous or heterologous subtype adr and ayw virus of human serum source. This is the first example of a vaccine produced from recombinant cells which is effective against a human viral infection. 相似文献
989.
Molecular cloning of cDNA encoding a murine haematopoietic growth regulator, granulocyte-macrophage colony stimulating factor 总被引:5,自引:0,他引:5
N M Gough J Gough D Metcalf A Kelso D Grail N A Nicola A W Burgess A R Dunn 《Nature》1984,309(5971):763-767
DNA clones specifying the murine granulocyte-macrophage colony stimulating factor have been isolated. This haematopoietic growth factor is encoded by a unique gene specifying a messenger RNA of 1,200 nucleotides and a polypeptide of 118 amino acids. It bears no structural similarity to the functionally related factor, interleukin-3, described recently. 相似文献
990.
Role for microsomal Ca storage in mammalian neurones? 总被引:4,自引:0,他引:4
Alterations in the intracellular concentration of calcium ions [( Ca2+]i) are increasingly being found to be associated with regulatory functions in cells of all kinds. In muscle, an elevation of [Ca2+]i is the final link in excitation-contraction coupling while at nerve endings and in secretory cells, similar rises in [Ca2+]i are thought to mediate exocytosis. The discovery of calcium-activated ion channels indicated a role for intracellular calcium in the regulation of membrane excitability. Calcium transients associated with either intracellular release or the inward movement of Ca2+ across the membrane have been recorded in molluscan neurons and more recently in neurones of bullfrog sympathetic ganglia. Here, we report the first recordings of calcium transients in single mammalian neurones. In these experiments we have found that the methylxanthine, caffeine, causes the release of calcium from a labile intracellular store which can be refilled by Ca2+ entering the cell during action potentials. 相似文献