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31.
The interaction of vanadate with the Ca2+-ATPase of sarcoplasmic reticulum vesicles has been studied by making use of the ATPase activity as a measure of uncomplexed enzyme. The binding/dissociation is slow, so that initial rates can be used to study the equilibrium binding. The results indicate that in addition to a Ca2+-free complex E.Van (KV = 0.4 microM), there must also be a Ca2+-enzyme-vanadate complex (K'V = 7 microM). This observation is confirmed by the difference between the kinetics of decay of activity on vanadate addition, and on addition of ATP to enzyme preincubated with vanadate and Ca2+, which requires two enzyme-vanadate complexes. ATP increases the apparent affinity of the enzyme for vanadate by inducing calcium release. Upper limits for the kinetic parameters for vanadate binding and dissociation are estimated. 相似文献
32.
The properties of periodic and aperiodic glycolytic oscillations observed in yeast extracts under sinusoidal glucose input were analyzed by the following methods. (1) Spectral analysis, rendering sharp peaks for periodic responses and enhanced broad-band noise for aperiodic oscillations. (2) Phase plane analysis, leading to closed and to open trajectories for periodic and aperiodic oscillations, respectively. (3) Rotation of a phase plane proportionally to time, revealing strange attractors associated with the aperiodic oscillations. (4) Stroboscopic plot on the phase plane, showing that the strange attractors follow a stretch-fold-press process, if the stroboscoping phase is varied. (5) Stroboscopic transfer plot, admitting a period of three transfer processes and thus implying chaos according to the Li-Yorke theorem. (6) Determination of the rate of information production by differentiation of the transfer plot, yielding approx. 0.21 bits per min for the chaotically glycolyzing yeast extract. 相似文献
33.
Adipose tissue kinetics of chlorpromazine and imipramine, two drugs which are more lipophilic than thiopental, were studied in the rat. After single i.v. doses, the time-course of drug distribution was followed in adipose and various other tissues, until their concentrations in adipose tissues declined. Under these conditions the two drugs behaved almost identically. Among the tissues analyzed, the lowest concentrations were found in adipose tissue, with the exception of plasma. At its maximum concentration after about 30 minutes, total adipose tissue contained only 3 % of the dose of administered drugs. Adipose/plasma and adipose/lung concentration ratios were 2–5 and 0.05, respectively.After maximum tolerated oral doses of imipramine for 3 weeks, similar steady state concentration ratios (plasma:adipose:brain:lung 1:3:12:96) were observed. In adipose tissue the imipramine/desmethylimipramine ratio was about 1, and the desmethylimipramine steady state levels did not increase with time. Literature data indicate that many basic lipophilic drugs are not stored in adipose tissue. This is now clearly shown for chlorpromazine and imipramine, even under extreme, subchronic conditions in the case of imipramine. 相似文献
34.
Y L Colson B H Markus A Zeevi R J Duquesnoy 《Journal of immunology (Baltimore, Md. : 1950)》1990,144(8):2975-2984
The interactions of alloreactive T lymphocytes with the vascular endothelium were studied in an in vitro model of lymphocyte adherence to cultured human arterial endothelial cell (HAEC) monolayers. Donor-primed lymphocytes (DPL) were shown to have significantly greater adherence to donor HAEC than were third-party primed lymphocytes. Limiting dilution analysis of adherent DPL showed an enrichment of donor-reactive lymphocytes compared with nonadherent DPL. This study examines the allospecific nature of this increased lymphocyte adherence. HAEC constitutively express class I HLA Ag and can be induced by IFN-gamma to express class II Ag. DPL adherence to class I+ HAEC was inhibited only in the presence of mAb directed against class I Ag. DPL adherence to class I+ and class II+ HAEC was inhibited in the presence of mAb directed against class I and class II Ag. Class I- and class II-specific adherence was also shown to involve CD8 and CD4 molecules, respectively, whereas lymphocyte function-associated Ag do not appear to play a major role in long term alloreactive lymphocyte adherence to HAEC. These findings suggest that alloreactive lymphocyte adherence to HAEC is mediated by two mechanisms. One is based on allorecognition, primarily of HLA Ag, and the other is related to presumably non-Ag-specific interactions between activated lymphocytes and the vascular endothelium. The studies presented provide evidence to suggest that HLA-specific lymphocyte adherence to endothelium may significantly contribute to the development of alloreactive lymphocyte infiltrates within the allograft. 相似文献
35.
Cysteine: Depolarization-Induced Release from Rat Brain In Vitro 总被引:3,自引:2,他引:1
Hans Jörg Keller Kim Quang Do Markus Zollinger Kaspar H. Winterhalter Michel Cuénod 《Journal of neurochemistry》1989,52(6):1801-1806
Compounds released on depolarization in a Ca2+-dependent manner from rat brain slices were screened to identify candidates for neuroactive substances. Lyophilized superfusates were analyzed by reversed-phase HPLC after derivatization with 9-fluorenyl N-succinimidyl carbonate. One of the compounds that showed an increase of concentration in superfusates in the presence of iodoacetamide was identified as the cysteine (Cys) derivative, S-carboxamidomethylcysteine, by fast atom bombardment mass spectrometry and other methods. This stable Cys derivative originates from endogenous, extracellular Cys. The finding led to a method for quantification of Cys in superfusates by immediate cooling of the superfusates to 0 degrees C and reaction of Cys with N-ethylmaleimide. Depolarization-induced Ca2+-dependent release of Cys was most prominent in the neocortex, followed by the mesodiencephalon, striatum, and cerebellum. This suggests that Cys is released from a neuronal compartment and might be involved in neurotransmission. 相似文献
36.
Daniel Gygax Henk Nachtegaal Oreste Ghisalba René Lattmann Hans-Peter Schär Christian Wandrey Markus B. Streiff 《Applied microbiology and biotechnology》1990,32(6):621-626
Summary The production of d-ribulose-5-phosphate in an enzyme membrane reactor was examined. Phosphoryl transfer from ATP to d-ribulose was catalysed by d-ribulokinase isolated from Klebsiella pneumoniae. For production of d-ribulose-5-phosphate the phosphoryl donor ATP was used either in stoichiometric or in catalytic amounts. Using catalytic amounts of ATP requires a second enzyme, e.g. pyruvate kinase, to regenerate ATP. The kinetic parameters for d-ribulokinase and pyruvate kinase were determined to calculate the performance of an enzyme membrane reactor for continuous production of d-ribulose-5-phosphate. Both processes operated for more than 200 h. Regardless of whether ATP was used in catalytic or stoichiometric amounts, about the same production parameters were determined. In continuous production space/time yields of 117 g (with ATP regeneration) and 103 g (without ATP regeneration) of d-ribulose-5-phosphate 1–1 per day were reached.Offprint requests to: D. Gygax 相似文献
37.
Gutmann Markus; von Aderkas Patrick; Label Philippe; Lelu Marie-Anne 《Journal of experimental botany》1996,47(12):1905-1917
Somatic embryos of hybrid larch (Larixleptoeuropaea) whichhad been matured for 4 weeks on maturation medium, developednormally on medium supplemented with 60 µM ABA, but abnormallyon medium with no ABA. A comparative structural and histochemicalinvestigation was carried out on these two types of mature embryos.At the light microscope level, differences between both treatmentswere visible only after 23 weeks of maturation. At aroundthis time, abnormal development becomes evident macroscopically:ABA-minus embryos remain rather stubby as opposed to the morecylindrically shaped ABA-plus embryos. Whereas somatic embryosmatured with ABA consist of densely cytoplasmic cells showinga high rate of cell division, ABA-minus embryos are largelymade up of expanded and highly vacuolate cells, indicating thatgrowth in the latter is mainly due to cell expansion and notdivision. After 4 weeks of maturation, ABA-minus embryos beginto elongate in the hypocotyl region, and precocious germinationwas observed frequently. Again, these morphogenetic events werelargely due to abnormal timing of cell expansion. Histochemically,storage proteins were found only in somatic embryos maturedfor 4 weeks with ABA. This observation is in line with resultsobtained by total protein analysis, yielding significantly lowertotal protein contents in ABA-minus embryos both on a freshweight and a per embryo basis after 45 weeks of maturation.Deposition of starch grains mainly in the cortex tissue of thehypocotyl region was observed within 2 weeks of maturation invarying amounts regardless of ABA supply. Polyphenols, in particularcatechins and proanthocyanidins, were present in all embryosfrom the very onset of development. They were localized preferentiallyin the proximal suspensor cells and the basal region of theembryo. However, accumulation of polyphenols was generally muchmore pronounced in embryos matured without ABA, indicating alack of biochemical regulatory competence in those embryos. Key words: Abscisic acid, embryonal development, somatic embryo, storage protein, polyphenols 相似文献
38.
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40.
Markus Kurz Karin Schütz Michael Göbel 《Origins of life and evolution of the biosphere》1996,26(3-5):263-264