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  • 1
    Electronic Resource
    Electronic Resource
    Characterization of Nucleotide Transport into Rat Brain Synaptic Vesicles (1999)
    Oxford UK : Blackwell Science Ltd
    Journal of neurochemistry 73 (1999), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract : ATP transport to synaptic vesicles from rat brain has been studied using the fluorescent substrate analogue 1,N6-ethenoadenosine 5′-triphosphate (ε-ATP), The increase in intravesicular concentration was time dependent for the first 30 min, ε-ATP being the most abundant nucleotide. The complexity of the saturation curve indicates the existence of kinetic and allosteric cooperativity in the nucleotide transport, which exhibits various affinity states with K0.5 values of 0.39 ± 0.06 and 3.8 ± 0.1 mM with ε-ATP as substrate. The Vmax values obtained were 13.5 ± 1.4 pmol · min-1· mg of protein-1 for the first curve and 28.3 ± 1.6 pmol · min-1· mg of protein-1 considering both components. This kinetic behavior can be explained on the basis of a mnemonic model. The nonhydrolyzable adenine nucleotide analogues adenosine 5′-O-3-(thiotriphosphate), adenosine 5′-(β,γ-imino)triphosphate and the diadenosine polyphosphates P1,P3-di(adenosine)triphosphate, P1,P4-di(adenosine)tetraphosphate, and P1,P5-di(adenosine)pentaphosphae the nucleotide transport. The mitochondrial ATP/ADP exchange inhibitor atractyloside, N-ethylmaleimide, and polysulfonic aromatic compounds such as Evans blue and 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid also inhibit ε-ATP vesicular transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1999.0731098.x
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  • 2
    Electronic Resource
    Electronic Resource
    Dinucleotide Receptor Modulation by Protein Kinases (Protein Kinases A and C) and Protein Phosphatases in Rat Brain Synaptic Terminals (1997)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 68 (1997), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The diadenosine polyphosphates, diadenosine tetraphosphate and diadenosine pentaphosphate (Ap5A), can activate an ionotropic dinucleotide receptor that induces Ca2+ transients into synaptosomes prepared from rat brain. This receptor, also termed the P4 purinoceptor, is sensitive only to adenine dinucleotides and is insensitive to ATP. Studies on the modulatory role of protein kinase A (PKA), protein kinase C (PKC), and protein phosphatases on the response of diadenosine polyphosphate receptors were performed by measuring the changes in the intracellular Ca2+ levels with fura-2. Activation and inhibition of PKA were carried out by means of forskolin and the PKA inhibitory peptide (PKA-IP), respectively. The Ap5A response was inhibited by forksolin to 35% of control values, but PKA-IP induced an increase of 37%. The effect of PKC activation was similar to that observed for PKA. PKC stimulation with phorbol 12,13-dibutyrate produced an inhibition of 67%, whereas the PKC inhibitors staurosporine and PKC inhibitory peptide enhanced the responses elicited by Ap5A to 40% in both cases. Protein phosphatase inhibitors diminished the responses elicited by Ap5A to 17% in the case of okadaic acid, to 50% for microcystin, and to 45% in the case of cyclosporin A. Thus, the activity of dinucleotide receptors in rat brain synaptosomes appears to be modulated by phosphorylation/dephosphorylation. These processes could be of physiological significance in the control of transmitter release from neurons that are postsynaptic to nerves that release diadenosine polyphosphates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1997.68062552.x
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  • 3
    Electronic Resource
    Electronic Resource
    Exchange-bias systems with compensated interfaces (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3995-3997 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When a ferromagnetic metal (F) is in contact with an antiferromagnet (AF), often a shift of the hysteresis loop away from its normal, symmetric position around H=0, to HE≠0 does occur. This phenomenon is known as exchange bias (EB). We put forward an analytic model, for compensated AF interfaces, based on the AF interface freezing into a metastable canted spin configuration. The EB energy is reversibly stored in a spring-like magnet, or incomplete domain wall, in the F slab. Our theory yields the right values of HE and its F thickness dependence HE∝tF−1. It also predicts the F layer by layer magnetization profile. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125517
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetic study and mathematical modelling of killer and sensitive S. Cerevisiae strains growing in mixed culture (1997)
    Springer
    Bioprocess engineering 17 (1997), S. 375-381 
    Details
    ISSN: 0178-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  This paper presents a kinetic study of two yeasts growing in pure and mixed batch cultures. Two winemaking strains were used: S. cerevisiae K1 possessing the K2 killer character and S. cerevisiae 522D sensitive to the K2 killer toxin. Initially the kinetics of growth of the two strains were analysed in pure culture. In this case, the kinetic profiles of biomass production have shown that the growth rate of the K1 strain is slightly superior to the 522D strain. During the fermentation, the viability for both populations was higher than 90%. Fermentations in mixed culture with an initial percentage in killer strain of 5 and 10% with respect to the total population were carried out. The results showed a more important decrease in the percentage of total viable yeasts when the initial concentration of killer yeast increased. However, the kinetic profiles of total biomass (killer plus sensitive yeasts) were very similar for both fermentations. A mathematical model was proposed to simulate the microbial growth of the killer and sensitive strain developing in pure and mixed cultures. This mathematical model consists in three main reactions: the evolution of the killer toxin in the culture medium, the duplication and the mortality rates for each microbial population. The results of the simulation appeared in agreement with the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00008970
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  • 5
    Electronic Resource
    Electronic Resource
    Mixed culture of killer and sensitive Saccharomyces cerevisiae strains in batch and continuous fermentations (1997)
    Springer
    World journal of microbiology and biotechnology 14 (1997), S. 83-87 
    Details
    ISSN: 1573-0972
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract This paper presents a kinetic study of the dynamics of the population of two Saccharomyces cerevisiae strains (designated K1 and 522D) in mixed culture. These two strains are commonly used in wine making. The K1 strain (killer yeast) secretes a glycoprotein (killer toxin) which causes the death of the 522D strain (sensitive yeast). Initially, the mixed cultures were realized in batch fermentations. Initial concentrations of killer yeast were 5 and 10% of the total population. The influence of the killer strain on the sensitive cultures was measured in comparison with a reference fermentation. The reference fermentation was inoculated only with the sensitive strain. Results show that an initial concentration of 10% of killer strain affects the microbial population balance and the rate of ethanol production. However the fermentation was only slightly disturbed when the proportion of killer to sensitive yeast at the beginning of mixed culture was 5%. To achieve total displacement by the killer yeast at low concentrations, the mixed cultures were carried out in a continuous system. The results obtained in continuous fermentations with the same strains have shown that a level of contamination as low as 0.8% of killer strain was sufficient to completely displace the original sensitive population after 150 h incubation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008880618359
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of Phosphorus and Endomycorrhiza (Glomus Intraradices) on gas exchange and plant growth of Chile Ancho Pepper (Capsicum Annuum L. cv. San Luis) (1999)
    Springer
    Photosynthetica 36 (1999), S. 441-449 
    Details
    ISSN: 1573-9058
    Keywords: fruit ; internal CO2 concentration ; leaf area ratio ; leaf number and area ; net photosynthetic rate ; phosphorus use efficiency ; root ; shoot ; stomatal conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Seedlings of chile ancho pepper were grown in pots containing a pasteurized mixture of sand and a low phosphorus (P) sandy loam soil, and either inoculated (VAM) or not inoculated (NVAM) with the endomycorrhizal fungus Glomus intraradices. Long Ashton nutrient solution (LANS) was modified to supply P to the seedlings at 0, 11, and 44 g(P) m-3 (P0, P11, P44, respectively). Low P depressed net photosynthetic rate (PN), stomatal conductance (gs), phosphorus use efficiency (PN/P), and internal CO2 concentration (Ci). The mycorrhiza alleviated low P effects by increasing PN, gs, PN/P, and decreasing Ci. At P0, Ci of NVAM plants was equal to or higher than that of VAM plants, suggesting nonstomatal inhibition of photosynthesis. Gas exchange of VAM plants at P0 was similar to that of NVAM plants at P11. Endomycorrhiza increased leaf number, leaf area, shoot, root and fruit mass at P0 and P11 compared to NVAM plants. Reproductive growth was enhanced by 450 % in mycorrhizal plants at P44. Root colonization (arbuscules, vesicles, internal and extraradical hyphae development) was higher at lower P concentrations, while sporulation was unaffected. The enhanced growth and gas exchange of mycorrhizal plants was in part due to greater uptake of P and greater extraradical hyphae development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007032320951
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  • 7
    Electronic Resource
    Electronic Resource
    Kinetic Study and Mathematical Modelling of the Growth of S. cerevisiae 522D in Presence of K2 Killer Protein (1997)
    Chichester : Wiley-Blackwell
    Journal of Chemical Technology AND Biotechnology 68 (1997), S. 195-201 
    Details
    ISSN: 0268-2575
    Keywords: Saccharomyces cerevisiae ; alcoholic fermentation ; killer yeasts ; sensitive yeasts ; mathematical model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: --This paper deals with the study of the kinetics of batch fermentations for a sensitive strain of S. cerevisiae growing in a culture medium containing K2 killer protein. The inhibition due to the killer toxin was measured by the reduction of the viable biomass, ethanol production and glucose consumption compared with a reference fermentation. The reference culture was run under the same conditions, but using a heat-denatured solution of killer protein. Results showed a decrease of the viable population of 67·8% after 15 h incubation. The fermentation time for the total consumption of the glucose was significantly affected by the presence of the killer toxin. The specific rate of ethanol production was also affected during the fermentation. However, the yields of ethanol and biomass were very similar for both fermentations. A kinetic mathematical model was proposed to explain the dynamics of the S. cerevisiae 522D growth in the presence of the K2 killer protein. The results of the suggested simulation were in agreement with the experimental data. © 1997 SCI.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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