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81.
The excitatory neurotransmitter, glutamate, generates a characteristic burst-pause type of firing in midbrain dopamine neurons in association with the reward behavior, but the cellular mechanism by which glutamate generates these bursts is unknown. Here, we show that the bursts in spontaneously firing dopamine neurons can be generated by the combinative actions of the brief stimulatory and the subsequent Ca(2+)-dependent inhibitory signals in response to glutamate stimulation. The two Ca(2+)-dependent firing-extinction signals are activated by different glutamate receptors. Although the activation of metabotropic glutamate receptors rapidly stopped the enhanced firing through the Ca(2+) release from intracellular stores, the activation of NMDA and AMPA/kainate receptors abolished the firing immediately after termination of the stimulation due to the Ca(2+) accumulation in the cell. These two Ca(2+)-dependent inhibitory mechanisms appear to participate in the generation of characteristic bursts in dopamine neurons by controlling the maximum firing number of single bursts and the duration of post-firing pauses. 相似文献
82.
83.
Barley aleurone cells contain two types of vacuoles. Characterization Of lytic organelles by use of fluorescent probes 总被引:10,自引:1,他引:9 下载免费PDF全文
Light microscopy was used to study the structure and function of vacuoles in living protoplasts of barley (Hordeum vulgare cv Himalaya) aleurone. Light microscopy showed that aleurone protoplasts contain two distinct types of vacuole: the protein storage vacuole and a lysosome-like organelle, which we have called the secondary vacuole. Fluorescence microscopy using pH-sensitive fluorescent probes and a fluorogenic substrate for cysteine proteases showed that both protein storage vacuoles and secondary vacuoles are acidic, lytic organelles. Ratio imaging showed that the pH of secondary vacuoles was lower in aleurone protoplasts incubated in gibberellic acid than in those incubated in abscisic acid. Uptake of fluorescent probes into intact, isolated protein storage vacuoles and secondary vacuoles required ATP and occurred via at least two types of vanadate-sensitive, ATP-dependent tonoplast transporters. One transporter catalyzed the accumulation of glutathione-conjugated probes, and another transported probes not conjugated to glutathione. 相似文献
84.
Tai-Boong Uhm Si-Myung Byun Young-Ju Kwon Sang-Bae Han Kwan-Sung Ryu 《Biotechnology letters》1987,9(4):287-290
Summary The three fractions of inulase differing in isoelectric pH were isolated from a strain ofAspergillus
niger by isoelectric focussing and characterized in their temperature stability. These fractions had distinguishable thermal stability. Among them, one fraction (pI 5.2) having main activity showed a high thermal stability comparable to that of the Novozyme 230 (Novo A/S, Denmark) at 60°C. 相似文献
85.
M H Walter E M Westbrook S Tykodi A M Uhm E Margoliash 《The Journal of biological chemistry》1990,265(8):4177-4180
Previous crystallographic studies of tuna ferricytochrome c have employed crystals grown from solutions of ammonium sulfate, corresponding to an ionic strength of 9.5 M (Takano, T., and Dickerson, R. E. (1981) J. Mol. Biol. 153, 95-115). To obtain a structure at a lower ionic strength, the ferric tuna protein was crystallized at neutral pH with polyethylene glycol at an ionic strength of 45 mM, These crystals (space group P2(1), a = 37.11 A, b = 107.66 A, c = 55.75 A, beta = 105.3 degrees) contain four molecules/asymmetric unit and grow to dimensions of 0.2 X 0.4 X 1.0 mm in 2-4 weeks. They diffract to beyond 1.8 A and are stable in the x-ray beam. We have recorded 28,198 unique Bragg reflections (83% of those possible) to a resolution of 1.89 A from a native crystal. We are undertaking a solution of this structure by the molecular replacement method. 相似文献
86.
Dara Leto Maeran Uhm Anja Williams Xiao-wei Chen Alan R. Saltiel 《The Journal of biological chemistry》2013,288(13):9272-9283
RGC1 and RGC2 comprise a functional RalGAP complex (RGC) that suppresses RalA activity. The PI3-kinase/Akt signaling pathway activates RalA through phosphorylation-mediated inhibition of the RGC. Here we identify a novel phosphorylation-dependent interaction between 14-3-3 and the RGC. 14-3-3 binds to the complex through an Akt-phosphorylated residue, threonine 715, on RGC2. Interaction with 14-3-3 does not alter in vitro activity of the GTPase-activating protein complex. However, blocking the interaction between 14-3-3 and RGC2 in cells increases suppression of RalA activity by the RGC, suggesting that 14-3-3 inhibits the complex through a non-catalytic mechanism. Together, these data show that 14-3-3 negatively regulates the RGC downstream of the PI3-kinase/Akt signaling pathway. 相似文献
87.
Ethyl (R, S)-4-chloro-3-hydroxybutanoate (ECHB) is a useful chiral building block for the synthesis of L-carnitine and hypercholesterolemia drugs. The yeast reductase, YOL151W (GenBank locus tag), exhibits an enantioselective reduction activity, converting ethyl-4-chlorooxobutanoate (ECOB) exclusively into (R)-ECHB. YOL151W was generated in Escherichia coli cells and purified via Ni- NTA and desalting column chromatography. It evidenced an optimum temperature of 45 degrees C and an optimum pH of 6.5-7.5. Bacillus subtilis glucose dehydrogenase (GDH) was also expressed in Escherichia coli, and was used for the recycling of NADPH, required for the reduction reaction. Thereafter, Escherichia coli cells co-expressing YOL151W and GDH were constructed. After permeablization treatment, the Escherichia coli whole cells were utilized for ECHB synthesis. Through the use of this system, the 30 mM ECOB substrate could be converted to (R)-ECHB. 相似文献
88.
A Survey of the Brassica rapa genome by BAC-end sequence analysis and comparison with Arabidopsis thaliana 总被引:1,自引:0,他引:1
Hong CP Plaha P Koo DH Yang TJ Choi SR Lee YK Uhm T Bang JW Edwards D Bancroft I Park BS Lee J Lim YP 《Molecules and cells》2006,22(3):300-307
Brassica rapa ssp. pekinensis (Chinese cabbage) is an economically important crop and a model plant for studies on polyploidization and phenotypic evolution. To gain an insight into the structure of the B. rapa genome we analyzed 12,017 BAC-end sequences for the presence of transposable elements (TEs), SSRs, centromeric satellite repeats and genes, and similarity to the closely related genome of Arabidopsis thaliana. TEs were estimated to occupy 14% of the genome, with 12.3% of the genome represented by retrotransposons. It was estimated that the B. rapa genome contains 43,000 genes, 1.6 times greater than the genome of A. thaliana. A number of centromeric satellite sequences, representing variations of a 176-bp consensus sequence, were identified. This sequence has undergone rapid evolution within the B. rapa genome and has diverged among the related species of Brassicaceae. A study of SSRs demonstrated a non-random distribution with a greater abundance within predicted intergenic regions. Our results provide an initial characterization of the genome of B. rapa and provide the basis for detailed analysis through whole-genome sequencing. 相似文献
89.
90.
Oxytocin is a mammalian hormone that is released mainly after distension of the uterine cervix. In this study, we report that oxytocin stimulates intracellular release of calcium, and also activates AMPK (AMP-activated protein kinase) in C2C12 myoblast cells in a time/dose-dependent manner. Oxytocin receptor mRNA was detected in C2C12 cells. In addition, oxytocin stimulated glucose uptake and, moreover, inhibition of either CaMKK (Ca(2+)/calmodulin-dependent protein kinase kinase) or AMPK blocked oxytocin-mediated AMPK activation and glucose uptake. Taken together, our findings suggest that oxytocin may serve a peripheral metabolic function in skeletal muscle cells through the calcium-CaMKK-AMPK pathway. 相似文献