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261.
Maura Turriani Rossana Pesi Antonella Nardone Gino Turchi Francesco Sgarrella Pier Luigi Ipata Maria Grazia Tozzi 《Journal of biochemical and molecular toxicology》1994,9(1):51-57
Nucleoside phosphotransferase acting on inosine and deoxyinosine has been partially purified from cultured Chinese hamster lung fibroblasts (V79). The activity is associated with a cytosolic 5′-nucleotidase acting on IMP and deoxyIMP. The transfer of the phosphate group from IMP to inosine catalyzed by this enzyme was activated by ATP and 2,3-bisphosphoglycerate. Inosine, deoxyinosine, guanosine, deoxyguanosine, and the nucleoside analogs 2′,3′-dideoxyinosine and 8-azaguanosine are substrates, while adenosine and deoxyadenosine are not. IMP, deoxyIMP, GMP, and deoxyGMP are the best phosphate donors. The cytosolic 5′-nucleotidase/phosphotransferase substrate, 8-azaguanosine, was found to be very toxic for cultured fibroblasts (LD50 = 0.32 μM). Mutants resistant to either 8-azaguanosine and the correspondent base 8-azaguanine were isolated and characterized. Our results indicated that the 8-azaguanosine-resistant cells were lacking both cytosolic 5′-nucleotidase and hypoxanthine-guanine phosphoribosyltransferase, while 8-azaguanine resistant cells were lacking only the latter enzyme. Despite this observation, both mutants displayed 8-azaguanosine resistance, thus indicating that cytosolic 5′-nucleotidase is not essential for the activation of this nucleoside analog. 相似文献
262.
Calcium/Calmodulin-Stimulated Protein Kinase II Is Present in Primary Cultures of Cerebral Endothelial Cells 总被引:1,自引:0,他引:1
Mária A. Deli Ferenc Joó István Krizbai Imre Lengyel Maria G. Nunzi Joachim R. Wolff† 《Journal of neurochemistry》1993,60(5):1960-1963
Abstract: Calcium/calmodulin-stimulated protein kinase II (CaMPK II). a major kinase in brain, has been established to play an important role in neurotransmitter release and organization of postsynaptic receptors, and it is known to be involved in long-term potentiation and memory. Less is known about the function of this enzyme in nonneural cells. Here we report on the production, presence, and phosphorylation of the α-subunit of CaM-PK II in primary cultures of cerebral endothelial cells. These results raise the possibility that α-CaM-PK II can act as one of the key enzymes of calcium-mediated intracellular signaling in the cerebral endothelial cells and suggest that α-CaM-PK II may participate in such basic cellular processes as permeability in physiological and pathological conditions. 相似文献
263.
Abstract: A possible role for protein kinases in the regulation of free cytosolic Ca2+ levels in nerve endings was investigated by testing the effect of several kinase inhibitors on the increase in cytosolic Ca2+ (monitored with the Ca2+ -sensitive dye fura-2) induced by depolarization with 15 or 30 mM K+ . The ability of various drugs to inhibit the cytosolic Ca2+ response appeared to correlate with their reported mechanism of action in inhibiting protein kinases. W-7 and trifluoperazine, drugs reported to inhibit calmodulin-dependent events, were effective inhibitors of the increase in cytosolic Ca2+ induced by high K+ depolarization, as was sphingosine, a drug that inhibits protein kinase C by binding to the regulatory site, but which also inhibits calcium/calmodulin kinase. On the other hand, drugs that inhibit protein kinases by binding to the catalytic site, such as H-7 (1 m/W ), staurosporine (1μ M ), and K252a (1μ M ), were ineffective. Activation of protein kinase C, which is blocked by each of these drugs, does not appear to be essential to the maintenance of elevated cytosolic Ca2+ in depolarized synaptosomes. All of the drugs, including sphingosine, that functionally inhibit the depolarization-induced elevation in cytosolic Ca2+ have in common the ability to bind to calmodulin. Because the drugs that inhibit protein kinases by competing with ATP binding at the active catalytic site did not block the response in this system, we suggest that a calmodulin or a calmodulin-like binding site participates in the regulation of Ca2+ increases after depolarization. 相似文献
264.
Maria A. Faust 《Journal of phycology》1993,29(1):100-107
Three new benthic dinoflagellate species, Prorocentrum belizeanum, Prorocentrum elegans, and Prorocentrum caribbaeum, from mangrove floating detritus are described from scanning electron micrographs. Species were identified based on shape, size, surface micromorphology, ornamentation of thecal plates, and architecture of the periflagellar area and intercalary band. Cells of P. belizeanum are round to slightly oval with a cell size of 55–60 μm long and 50–55 μm wide. Areolae are round and numerous (853–1024 per valve) and range from 0.66 to 0.83 μm in size. The periflagellar area of P. belizeanum is a broad V-shaped depression; it accommodates a flagellar and an auxiliary pore and a flared, curved apical collar. The intercalary band of P. belizeanum is horizontally striated. Prorocentrum elegans is a small species 15–20 μm long and 10–14 μm wide, with an ovate cell shape. The thecal surface is smooth. Two sizes of valve pores were recognized: large, round pores (20–22 per valve) arranged in a distinct pattern and smaller pores situated in an array along the intercalary band. The periflagellar area is V-shaped; it accommodates an uneven sized flagellar pore, an auxiliary pore, and an angled protuberant flagellar plate. The intercalary band is transversely striated. It is a bloom-forming species. Prorocentrum caribbaeum cells are heart-shaped with a rounded anterior end and a pointed posterior end. Cells range from 40 to 45 μm long and 30 to 35 μm wide. Thecal surface has two different-sized pores: large, round pores (145–203 per valve) arranged perpendicularly from the posterior margins, and small, round pores unevenly distributed on the thecal surface. The periflagellar area is ornate. It is V-shaped with a curved apical collar located next to the auxiliary pore; a smaller protuberant apical plate is adjacent to the flagellar pore. The intercalary band is transversely striated and sinuous. Cells are active swimmers. 相似文献
265.
Inga Sidén-Kiamos Guido Favia Dora Artiaco Giuseppe Saceone Maria Furia Lino C. Bolito Christos Louis 《Genetica》1993,92(1):43-53
The sequence determination of several genomic clones isolated from the Mediterranean fruitfly Ceratitis capitata identified the existence of opa-like repeats, often more than one being clustered in small chromosomal segments. These repeats have previously been shown to consist of stretches of tandemly reiterated glutamine-encoding residues, and they are found in multiple genes of several organisms. Most of the repeats described here are flanked or interrupted by stop codons in all reading frames and, thus, could not possibly be part of protein-coding sequences. Furthermore, these repeats, of which there are several hundred in the genome of the Medfly, can be used effectively for the determination of sequence polymorphisms, providing a convenient approach to obtain additional landmarks for the construction of genomic maps of this economically important insect.This paper is dedicated to the memory of our colleague and friend Dr. Jim Flach who took part in the initial phase of this work and died during the course of the investigation. 相似文献
266.
Armengol-Díaz Javier Esparcia Angeles Vicente Eduardo Miracle Maria Rosa 《Hydrobiologia》1993,255(1):381-388
Vertical distribution of planktonic rotifers is described in relation to temperature and oxygen in Lake La Cruz, a single-doline, closed karstic lake (121 m diameter and 25 m maximum depth) which shows iron meromixis. Samples were taken by peristaltic pumping at 10 cm depth intervals in the oxycline zone from June 1987 to September 1988. A model of rotifer vertical structure in stratified lakes is proposed. Rotifers concentrate their populations at the depths with intense gradients. As stratification develops some rotifer populations show a downward migration following the thermocline and some others show an upward migration following the oxycline. The production-respiration balance in the lake, and so the position of the oxycline with respect to the thermocline and the layer of maximum production, depends on meteorological conditions. A shift in the dominance of congeneric or related species can occur in consecutive years. In Lake La Cruz, mixing conditions and subterranean inflow in spring were much more intense in 1988 than 1987, and the distance between production and decomposition depths was smaller in 1988. Anuraeopsis miraclei, an oxycline-bound species with high abundance in 1987, was displaced by A. fissa in 1988. A. fissa, which was a metalimnetic species during early summer, reached peak densities (3 × 104 ind l–1) at the oxycline, equaling the abundance of A. miraclei the preceeding year. 相似文献
267.
Vicente Gomes Phan Van Ngan Claude de Broyer Maria José deA. C. Rocha Passos 《Hydrobiologia》1993,262(2):109-113
Mitotic and meiotic chromosomes of the Antarctic lysianassoid amphipod Waldeckia obesa are described. The modal chromosome number is n = 25 and 2n = 50. The potential applications of cytogenetical studies in this group are discussed. 相似文献
268.
Maria R. Finckh Christopher C. Mundt 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1993,85(6-7):809-821
Summary Eighteen populations, composed of four wheat (Triticum aestivum) varieties that were originally mixed together at equal frequencies, were grown for one-to-three generations at two locations. In addition, pure stands of the four varieties were grown in each year. Populations were either exposed to two stripe rust (Puccinia striiformis) races, protected from stripe rust, or exposed to alternating years of diseased and disease-free conditions. Regression of the logit of a variety's frequency versus generation number was used to calculate the relative fitness of each variety in each population. These analyses suggest that the relative fitnesses of the wheat varieties were affected by disease and geographic location and were constant over time. However, frequency-changes of varieties in the mixtures were negatively correlated with their planting frequencies (0.0001 < P < 0.085 in 14 out of 16 cases), suggesting that fitnesses were frequency-dependent in both the presence and absence of disease. We hypothesize that failure to detect frequency-dependence of fitness in the logit analyses was due to a limited number of generations and a limited range of initial variety frequencies. This is supported by data from longer-term studies in the literature that provide evidence for frequency-dependence of fitness in plant mixtures. Analyses of currently available field data suggest that stable equilibria may be a more likely outcome for mixtures of varieties that are more closely related and/or more uniformly adapted to the environment in which they are grown.Paper No. 9820 of the journal series of the Oregon Agricultural Experiment Station. 相似文献
269.
The limited proteolytic pattern of transducin,G
t
, and its purified subunits with chymotrypsin were analyzed and the cleavage sites on the
t
subunit were identified. The
t
subunit in the GTPS bound form was cleaved into a major 38 kD fragment, whereas
t
-GDP was progressively digested into 38, 23, 21, and 15 kD fragments. The
t
subunit was not very sensitive to proteolytic digestion with chymotrypsin. The
t
subunit was not cleaved and only a small portion of
t
was digested into several fragments. In order to determine which proteolytic fragment of
t
still contained the carboxyl terminal region, chymotrypsinization was carried out usingG
t
previously32P-labeled at Cys347 by petrussis toxin-catalyzed ADP-ribosylation. The32P-label was mainly associated with the
t
subunit and a 15 kD fragment. The 23 and 21 kD fragments were not32P-labeled. Analysis of amino terminal sequences of 38, 21, and 15 kD proteolytic bands allowed the identification of the major cleavage sites. Chymotrypsin had two cleavage sites in the amino terminal region of
t
, at Leu15 and Leu19. Chymotrypsin removed 15–19 amino acid residues from the amino terminus of
t
, generating two peptides (38 kD) which comigrates in gel electrophoresis. Chymotrypsin also cleaved at Trp207 in a conformation-dependent manner. Trp207 of
t
-GTPS was resistant to proteolysis but
t
-GDP and the 38 kD fragments of
t
-GDP produced the 23 and 21 kD fragments, respectively, and a 15 kD fragment containing the carboxyl terminus. This proves that the environment of Trp207 changes when GTP or GTPS is bound, leading to its inaccessibility to chymotrypsin. 相似文献
270.
Andrew R. J. Curtis Sophie Headland Susan Lindsay Nicholas S. T. Thomas Eileen Boye Smaragda Kamakari Paul Roustan Maria Anvret Jan Wahlstrom Gillian McCarthy Angus J. Clarke Shomi Bhattacharya 《Human genetics》1993,90(5):551-555
Four families, each with two individuals affectecd by Rett Syndrome (RS), were analysed using restriction fragment lenght polymorphisms and microsatellite markers from the X chromosome. In two of the families, X-linked dominant inheritance of the RS defect from a germinally mosaic mother could be assumed. Therefore, maternal X chromosome markers showing discordant inheritance were used to exclude regions of the X chromosome as locations of the RS gene. Much of the short arm could be excluded, including regions containing three candidate genes, OTC, synapsin 1 and synaptophysin. Although most of the long arm was inherited in common it was possible to exclude a centromeric region. Inheritance of X chromosome markers is also presented for two families with affected aunt-niece pairs, one of which has not been previously studied at the DNA level. 相似文献