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21.
Andrea Streit reas Faissner Bernd Gehrig Melitta Schachner 《Journal of neurochemistry》1990,55(5):1494-1506
The monoclonal L5 antibody reacts with an N-glycosidically linked carbohydrate structure which is present on the neural cell adhesion molecule L1, neural chondroitin sulfate proteoglycans, and other not yet identified glycosylated proteins. Using this antibody, we isolated and characterized proteoglycans from adult mouse brain and cultured astrocytes biosynthetically labeled with Na2 35SO4 and a 3H-amino acid mixture. Our data suggest that the L5 proteoglycans of both sources are identical in their biochemical properties. The apparent molecular mass of the L5 proteoglycan is approximately 500 kDa. Digestion of the iodinated L5 proteoglycan from mouse brain and of the [35S]methionine-labeled L5 proteoglycan from cultured astrocytes with proteinase-free chondroitinases ABC and AC revealed three major core proteins with apparent molecular masses of approximately 380, 360, and 260 kDa. These represent molecularly distinct protein cores. 相似文献
22.
Summary Ion: solute cotransporters frequency are incapable of achieving equilibrium between the solute accumulation and the transmembrane difference of the electrochemical potential of the ion. The presence of uncoupled flows of ion and solutes (leaks) is often advanced as an explanation. Here an alternative is discussed. The net accumulation of solute may be so slow that equilibrium can never be attained at finite times (e.g., several hours). Cotransporters may exhibit strong product inhibition, and the net influx of solute approaches zero far from equilibrium. The inherent slowness of net transport under these conditions is termed catalytic inefficiency. The likelihood that galactoside: H+ cotransport inEscherichia coli, hexose: H+ cotransport inChlorella vulgaris, andd-glucose: Na+ cotransport in brush-border membranes exhibit catalytic inefficiency is examined. The existence of strong product inhibition complicates the determination of the stoichiometry of cotransport and the characterization of chemically modified or mutant cotransporters. 相似文献
23.
Sorbitol dehydrogenase (EC 1.1.1.14) was isolated from bovine brain and purified 3,000-fold to apparent homogeneity, as judged by polyacrylamide gel electrophoresis. The purified enzyme had a specific activity of 36 units/mg of protein; a molecular weight of 39,000 for each of the four identical subunits and 155,000 for the intact enzyme were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel exclusion chromatography, respectively. The presence of one Zn2+ per subunit was confirmed by atom absorption spectroscopy; inactivation of the enzyme by metal-chelating agents points to the essential role that Zn2+ plays in the catalytically competent enzyme. The enzyme is also inactivated by thiol-blocking reagents; with respect to inactivation by sodium pyrophosphate, sorbitol dehydrogenase is different from closely related alcohol dehydrogenase. 相似文献
24.
Creatine Transport in Cultured Cells of Rat and Mouse Brain 总被引:7,自引:3,他引:4
Astroglia-rich cultures derived from brains of newborn rats or mice use a transport system for the uptake of creatine. The uptake system is saturable, Na+-dependent, and highly specific for creatine and Na+. Kinetic studies on rat cells revealed a Km value for creatine of 45 microM, a Vmax of 17 nmol x h-1 x (mg of protein)-1, and a Km value of 55 mM for Na+. The carrier is competitively inhibited by guanidinopropionate (Ki = 15 microM). No such transport system was found in neuron-rich primary cultures from embryonic rat brain. It is hypothesized that creatine transport is an astroglial rather than a neuronal function. 相似文献
25.
Bernd Richard Knappmann Maria-Regina Kula 《Applied microbiology and biotechnology》1990,33(3):324-329
Summary Several strains of Gram-negative microorganisms were screened for maximum 3-deoxy-d-manno-2-octulosonic acid (KDO) aldolase (EC 4.1.2.23) activity. Although this enzyme has been noted to be inducible on special medium, no induction was found. By centrifugation studies the KDO aldolase was found to be localized in the cell wall or membrane fraction. The enzyme activity was very susceptible to small amounts of detergent in solution.
Offprint requests to: M.-R. Kula 相似文献
26.
Secretogranin II: Relative Amounts and Processing to Secretoneurin in Various Rat Tissues 总被引:2,自引:0,他引:2
Bernd Leitner Reiner Fischer-Colbrie Gerhard Scherzer Hans Winkler 《Journal of neurochemistry》1996,66(3):1312-1317
Abstract: Secretoneurin is a 33-amino-acid peptide produced in vivo from secretogranin II. An antiserum raised against this peptide recognizes both the free peptide and its precursors. By HPLC and radioimmunoassay we characterized the immunoreactive molecules and determined the levels of immunoreactivity in various rat organs. In adrenal medulla and to a lesser degree in the anterior pituitary processing of secretogranin II to secretoneurin was very limited, whereas in all other organs studied (brain, intestine, endocrine pancreas, thyroid gland, and posterior pituitary) a high degree of processing was apparent. Thus, practically all of the immunoreactivity was present as free secretoneurin. This was also true for serum. When the total amount of secretoneurin immunoreactivity was calculated for the various organs, the largest pools in descending order were in the intestine, CNS, anterior pituitary, pancreas, and adrenal gland. This makes it likely that secretoneurin in serum is mainly derived from the intestine. The high degree of processing of secretogranin II in most organs is consistent with the concept that this protein acts as a precursor of a functional peptide, i.e., secretoneurin. 相似文献
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Regulation of gap junction coupling in the developing neocortex 总被引:4,自引:0,他引:4
In the developing mammalian, neocortex gap junctions represent a transient, metabolic, and electrical communication system.
These gap junctions may play a crucial role during the formation and refinement of neocortical synaptic circuitries. This
article focuses on two major points. First, the influence of gap junctions on electrotonic cell properties will be considered.
Both the time-course and the amplitude of synaptic potentials depend,inter alia, on the integration capabilities of the postsynaptic neurons. These capabilities are, to a considerable extent, determined
by the electrotonic characteristics of the postsynaptic cell. As a consequence, the efficacy of chemical synaptic inputs may
be crucially affected by the presence of gap junctions.
The second major topic is the regulation of gap junctional communication by neurotransmitters via second messenger pathways.
The monoaminergic neuromodulators dopamine, nordrenaline, and serotonin reduce gap junction coupling via activation of two
different intracellular signaling cascades—the cAMP/protein kinase A pathway and the IP3/Ca2+/protein kinase C pathway, 013 respectively. In addition, gap junctional
communication seems to be modulated by the nitric oxide (NO)/cGMP system. Since NO production can be stimulated by glutamate-induced
calcium influx, the NO/cGMP-dependent modulation of gap junctions might represent a functional link between developing glutamatergic
synaptic transmission and the gap junctional network. Thus, it might be of particular importance in view of a role of gap
junctions during the process of circuit formation. 相似文献