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81.
Protein Kinase C Activation Attenuates N-Methyl-d-Aspartate-Induced Increases in Intracellular Calcium in Cerebellar Granule Cells 总被引:1,自引:0,他引:1
Lawrence D. Snell Karen R. lorio Boris Tabakoff Paula L. Hoffman 《Journal of neurochemistry》1994,62(5):1783-1789
Abstract: Activation of the N-methyl-d -aspartate (NMDA) subtype of glutamate receptor increases levels of intracellular calcium and can lead to stimulation of protein kinase C activity. Several reports have demonstrated that stimulation of protein kinase C can, in turn, increase electrophysiological responses to NMDA in certain cells or in oocytes expressing certain NMDA receptor subunits. In the present study, the effects of protein kinase C activation on NMDA receptor-mediated increases in intracellular Ca2+ levels were investigated in primary cultures of rat cerebellar granule cells using fura-2 fluorescence spectroscopy. Pretreatment of the cells with the protein kinase C activator phorbol 12-myristate 13-acetate (PMA), but not the inactive analogue 4α-phorbol 12-myristate 13-acetate, inhibited NMDA-induced increases in intracellular Ca2+ levels. Coincubation of cells with PMA and the kinase inhibitor staurosporine or calphostin C blocked the PMA effect. The potency of NMDA was reduced twofold, and the potency of the NMDA receptor coagonist, glycine, to enhance the response to NMDA was decreased fourfold by pretreatment of cells with PMA. The effect on glycine was mimicked by pretreatment with okadaic acid, a protein phosphatase inhibitor. PMA treatment did not significantly alter Mg2+ inhibition of the NMDA response but decreased the potency of the competitive antagonist CGS-19755. These data suggest that, in cerebellar granule cells, the function of the NMDA receptor may be subject to feedback inhibition by protein kinase C stimulation. Under physiological conditions, this inhibition may result from a decreased effectiveness of the endogenous coagonists, glutamate and glycine. 相似文献
82.
The variation for embryo production in anther ofSolanum phureja was examined as a function of maximum greenhouse temperature prior to bud harvest and innate responsiveness among anthers within a bud. Four clones ofS. phuyreja were grown in a greenhouse under a 16-h photoperiod. The temperature was monitored continuously. Buds (60 per day on 10 days) were collected and the anthers cultured in two groups of five flasks (30 anthers per flask). In the first group, each flask contained the 30 anthers from six buds; in the second group, each flask contained one anther from each of 30 buds. Significantly smaller coefficients of variation were observed for the second group, suggesting that variation for embryogenic capcity among buds was greater than that among anthers within a bud. Variation in embryo yield as a function of greenhouse temperature was examined by stepwise regression analysis. Embryogenic capacity of one clone was adversely affected by high temperatures (31–37°C) that occurred two and seven days before bud harvest. However, similarly high temperatures appeared to enhance the androgenic response of another clone. Conversion of anther-derived embryos over three subcultures to fresh regeneration medium was examined as a function of anther donor or clone, cold pretreatment of embryos, and morphological classification of embryos. Only clonal origin significantly affected conversion rate which ranged from 12.5% to 46.0%. Conversion rate declined on each serial subculture.Abbreviations BA
N6-benzyladenine
- GA3
gibberellic acid, IAA-indole-3-acetic acid 相似文献
83.
Gregory A. Ordway Peter S. Widdowson Karen Streator Smith Angelos Halaris 《Journal of neurochemistry》1994,63(2):617-624
Abstract: The binding of an agonist, p-[125I]iodoclonidine, and an antagonist, [3H]yohimbine, to α2-adrenoceptors was measured autoradiographically in the locus coeruleus from 10 pairs of antidepressant-free victims of suicide and age-matched controls. Agonist binding to α2-adrenoceptors was significantly greater in the locus coeruleus from victims of suicide compared with control subjects. In contrast, antagonist binding to α2-adrenoceptors in the locus coeruleus did not differ significantly between control and suicide subjects. HPLC analysis of norepinephrine in tissue sections of the locus coeruleus did not reveal any differences between control subjects and suicide victims, suggesting that differences in agonist binding are not a result of differences in retention of the endogenous agonist norepinephrine in tissue sections. The increase in agonist binding to α2-adrenoceptors in the locus coeruleus of victims of suicide links an altered expression of the high-affinity state of autoinhibitory α2-adrenoceptors with suicide. 相似文献
84.
Arianna Lee Karen L. Clark Martin Fleischmann Markus Aebi Michael W. Clark 《Molecular & general genetics : MGG》1994,245(1):32-44
Prp20/Srm1, a homolog of the mammalian protein RCC1 in Saccharomyces cerevisiae, binds to double-stranded DNA (dsDNA) through a multicomponent complex in vitro. This dsDNA-binding capability of the Prp20 complex has been shown to be cell-cycle dependent; affinity for dsDNA is lost during DNA replication. By analyzing a number of temperature sensitive (ts) prp20 alleles produced in vivo and in vitro, as well as site-directed mutations in highly conserved positions in the imperfect repeats that make up the protein, we have determined a relationship between the residues at these positions, cell viability, and the dsDNA-binding abilities of the Prp20 complex. These data reveal that the essential residues for Prp20 function are located mainly in the second and the third repeats at the amino-terminus and the last two repeats, the seventh and eighth, at the carboxyl-terminus of Prp20. Carboxyl-terminal mutations in Prp20 differ from amino-terminal mutations in showing loss of dsDNA binding: their conditional lethal phenotype and the loss of dsDNA binding affinity are both suppressible by overproduction of Gsp1, a GTP-binding constituent of the Prp20 complex, homologous to the mammalian protein TC4/Ran. Although wild-type Prp20 does not bind to dsDNA on its own, two mutations in conserved residues were found that caused the isolated protein to bind dsDNA. These data imply that, in situ, the other components of the Prp20 complex regulate the conformation of Prp20 and thus its affinity for dsDNA. Gsp1 not only influences the dsDNA-binding ability of Prp20 but it also regulates other essential function(s) of the Prp20 complex. Overproduction of Gsp1 also suppresses the lethality of two conditional mutations in the penultimate carboxyl-terminal repeat of Prp20, even though these mutations do not eliminate the dsDNA binding activity of the Prp20 complex. Other site-directed mutants reveal that internal and carboxyl-terminal regions of Prp20 that lack homology to RCC1 are dispensable for dsDNA binding and growth. 相似文献
85.
Heber Ulrich; Wagner Ute; Kaiser Werner; Neimanis Spidola; Bailey Karen; Walker David 《Plant & cell physiology》1994,35(3):479-488
Induction of photosynthesis in leaves was prolonged, and steadystate photosynthesis was inhibited by very high CO2 concentrationswhich cause cytoplasmic acidification. Prolonged exposure tohigh CO2 relieved initially observed inhibition of photosynthesisat least partially. The sensitivity of carbon assimilation tohigh CO2 was different in different plant species. Acidificationby CO2 (or subsequent alkalization) was detected by measuringrapid CO2-release from the tissue and by monitoring fluorescenceof pH-indicating dyes which had been fed to the leaves throughthe petiole. The results indicate that two different mechanismsoperate in leaves to achieve and maintain pH homeostasis. Rapidand efficient pH-adjustment is provided by proton/cation exchangeacross the tonoplast. Slower and less efficient regulation occursby formation or consumption of base. In the presence of highCO2 concentrations, protons are pumped from the cytosol intoalready acidic vacuoles. In turn, vacuolar cations replace exportedprotons in the cytosol permitting bicarbonate accumulation andincreasing the pH of the acidified cytosol. Similarly effectiveand fast proton/cation exchange relieves acid-stress in thechloroplast stroma and permits photosynthesis to proceed withhigh quantum efficiency or high light-saturated rates in thepresence of CO2 concentrations which would, in the absence offast cytoplasmic pH regulation, inhibit photosynthesis. By inference,proton/cation exchange must also occur across the mitochondrialboundary. After cytoplasmic pH adjustment in the presence ofhigh CO2, removal of CO2 results in transient cytoplasmic alkalizationand, subsequently, in the return of cytoplasmic pH values tolevels observed prior to acid-stress. In addition to fast pHregulation by rapid proton/cation exchange across biomembranes,slow base production (e.g. NH3-formation) also contributes torelieving acid stress. Base produced in the presence of highCO2 is rapidly consumed after removal of CO2. Implications of the findings in regard to forest damage by potentiallyacidic air pollutants such as SO2 are briefly discussed. (Received November 8, 1993; Accepted February 3, 1994) 相似文献
86.
The Lactococcus lactis sex-factor aggregation gene cluA 总被引:4,自引:0,他引:4
Jean-Jacques Godon Karen Jury Claire A. Shearman Michael J. Gasson 《Molecular microbiology》1994,12(4):655-663
A gene, cluA, was cloned from the chromosomally located sex factor of Lactococcus lactis MG1363. Sequence analysis revealed significant homology with previously described aggregation proteins in Enterococcus and Streptococcus species. The possibility that cluA was an equivalent protein involved in cell aggregation between donor and recipient bacteria during lactococcal conjugation was confirmed by its expression under the control of a heterologous promoter in L. lactis. Analysis of the homology between the CluA protein and the related proteins of Enterococcus and Streptococcus allowed a common structure for these proteins to be postulated. This consisted of five domains. Functionally conserved domains I and V act respectively as a secretary leader and C-terminal membrane anchor. Domains II and IV are conserved at the amino acid level and probably have common structural roles whereas domain III is variable and may control binding specificity. 相似文献
87.
High juvenile mortality in cheetahs (Acinonyx jubatus) and its consequences for maternal care 总被引:1,自引:0,他引:1
Juvenile mortality in cheetahs was found to be extremely high compared to other large mammals, with approximately 72.2% of litters dying before they emerged from the lair at eight weeks of age. An average of 83.3% of cubs alive at emergence died by adolescence at 14 months of age, thus cheetah cubs were estimated to have only a 4.8% chance of reaching independence at birth. The instantaneous rate of mortality was highest immediately after cubs emerged from the lair. Before emergence, lion predation was the major source of this mortality, although some cubs died from starvation after they were abandoned by their mothers, or as a result of grass fires and inclement weather. After emergence, predation again accounted for virtually all cub mortality, with lions and spotted hyaenas taking approximately the same proportion of cubs. Overall predation accounted for 73.2% of cheetah cub deaths in this study, with 78.2% of these being killed by lions. The extent of maternal care, in the form of vigilance and antipredator behaviour, mirrored cub susceptibility to mortality and, in the case of vigilance, possibly also starvation. The probability of a cheetah mother responding aggressively to a predator was found also to depend on the species of predator. This study highlights the importance of the influence of juvenile mortality on patterns of parental care. 相似文献
88.
Lora Swenson Ruth Green Rolf Joerger Michael Haas Karen Scott Yunyi Wei Urszula Derewenda David M. Lawson Zygmunt S. Derewenda 《Proteins》1994,18(3):301-306
A neutral lipase from the filamentous fungus Rhizopus delemar has been crystallized in both its proenzyme and mature forms. Although the latter crystallizes readily and produces a variety of crystal forms, only one was found to be suitable for X-ray studies. It is monoclinic (C2, a = 92.8 Å, b = 128.9 Å, c = 78.3 Å, β = 135.8) with two molecules in the asymmetric unit related by a noncrystallographic diad. The prolipase crystals are orthorhombic (P212121, with a = 79.8 Å, b = 115.2 Å, c = 73.0 Å) and also contain a pair of molecules in the asymmetric unit. Initial results of molecular replacement calculations using the refined coordinates of the related lipase from Rhizomucor miehei identified the correct orientations and positions of the protein molecules in the unit cells of crystals of both proenzyme and the mature form. © 1994 John Wiley & Sons, Inc. 相似文献
89.
John C. Spurlino Angela M. Smallwood Dennis D. Carlton Tracey M. Banks Karen J. Vavra Jeffrey S. Johnson Ewell R. Cook Joseph Falvo Robert C. Wahl Tricia A. Pulvino John J. Wendoloski Douglas L. Smith 《Proteins》1994,19(2):98-109
The X-ray crystal structure of a 19 kDa active fragment of human fibroblast collagenase has been determined by the multiple isomorphous replacement method and refined at 1.56 Å resolution to an R-factor of 17.4%. The current structure includes a bound hydroxamate inhibitor, 88 waters and three metal atoms (two zincs and a calcium). The overall topology of the enzyme, comprised of a five stranded β-sheet and three α-helices, is similar to the thermolysin-like metalloproteinases. There are some important differences between the collagenase and thermolysin families of enzymes. The active site zinc ligands are all histidines (His-218, His-222, and His-228). The presence of a second zinc ion in a structural role is a unique feature of the matrix metalloproteinases. The binding properties of the active site cleft are more dependent on the main chain conformation of the enzyme (and substrate) compared with thermolysin. A mechanism of action for peptide cleavage similar to that of thermolysin is proposed for fibroblast collagenase. © 1994 Wiley-Liss, Inc. 相似文献
90.
Mapping of Murine Fibroblast Growth Factor Receptors Refines Regions of Homology between Mouse and Human Chromosomes 总被引:1,自引:0,他引:1
Karen B. Avraham David Givol Aaron Avivi Avner Yayon Neal G. Copeland Nancy A. Jenkins 《Genomics》1994,21(3)
The genes for the fibroblast growth factor receptors Fgfr2, Fgfr3, and Fgfr4 have been mapped in the mouse using an interspecific backcross mapping panel. The Fgfr loci map to previously defined regions of homology between human and mouse chromosomes and provide additional information regarding human/mouse comparative mapping. 相似文献