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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Okadaic acid (OA) is a frequently used phosphatase inhibitor that by inhibiting dephosphorylation increases the net phosphorylation level in various systems. In the present study OA was used to assess the role of balanced phosphorylation-dephosphorylation reactions for successful regeneration of peripheral nerves. To achieve this, the effects of OA on phosphorylation levels, neurite outgrowth, injury-induced support cell proliferation, and neurofilament stability, respectively, were investigated in the in vitro regenerating, adult frog sciatic sensory nerve. OA at a moderate concentration (20 nM) increased phosphorylation levels and almost completely inhibited the in vitro regeneration in a reversible way. The effect on regeneration was not due to induced neurofilament instability and was only seen when the drug was applied in the outgrowth region. The latter and the absence of effects on support cell proliferation indicate that OA acts locally at the level of newly formed axons. However, the inhibition of regeneration was not a consequence of reduced delivery of proteins by axonal transport, because this process in fact was increased by OA. Altogether, the study suggests that properly balanced phosphorylating-dephosphorylating reactions are critical for regeneration of peripheral nerves.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 24 (1975), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Human glioma cells (138 MG) were found to take up 3-O-methyl-d-glucose (3-OMG) by a saturable low affinity transport system with a Km of 20 mm and a Vmax of 500 nmol/mg protein/min. About 20 per cent of the total uptake was due to passive diffusion. d-Glucose was a competitive inhibitor with a Ki of 10 mm. Follow-up experiments indicated that the same transport mechanism is involved in the uptake of n-glucose and 3-OMG. Phloretin (0·02 mm) and cytochalasin B (0·002 mm) strongly inhibited the uptake of 3-OMG, whereas phlorizin (0·02 mm), ouabain (0·1 mm), NaCN (0·5 mm) and iodoacetic acid (1·0 mm) had no effect. The data suggest that 3-OMG and d-glucose enter 138 MG cells mainly by a Na+-independent passive carrier-mediated transport system. Serum-deprivation doubled the population doubling time (Td) without affecting the total uptake of 3-OMG. An increase in the non-specific (diffusional) uptake was balanced by a decrease in the specific (carrier-medíated) uptake. After addition of dibutyryl cyclic AMP (dbcAMP, 0·25 mm) the cells attained a morphology characteristic of differentiated glia cells. Td was maintained unchanged. The non-specific uptake of 3-OMG was not affected in cells grown in serum-containing medium plus dbcAMP, whereas the specific uptake increased by 40 per cent and there-fore also the total uptake. Similar, but more pronounced, changes were observed if serum-deprived cells were treated with dbcAMP.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 19 (1972), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— An in vitro system from the frog has been used to study fast axonal protein transport. The preparation, which was incubated in a specially made chamber, consisted of the gastrocnemius muscle, the sciatic nerve, the dorsal ganglia and part of the spinal cord. The parts were separated from each other by silicone grease barriers, which made it possible to follow the migration of labelled proteins from the spinal cord and ganglia, along the sciatic nerve, towards the muscle. About 80 per cent of transported proteins in the sciatic nerve originated from the dorsal spinal ganglia and moved antidromically at a rate of 60–90 mm per day at 18°C. The rapidly transported proteins were 90 per cent particulate and mainly associated with structures sedimenting in the microsomal fraction.The effects of cyclohexirnide showed that the synthesis of rapidly moving proteins and their transport were separate processes. A low concentration of colchicine inhibited the transport when it was present in the medium surrounding the ganglia, but had no effect even at a higher concentration, when it was added to the nerve compartment. The presence of vinblastine at a low concentration in either of the two compartments completely arrested the protein transport. Likewise N-ethylmaleimide or p-chloromercuribenzene sulphonic acid in the nerve medium effectively blocked the fast transport. Results from experiments performed to test the possibility of disto-proximal flow and of transfer of proteins from the muscle to the nerve are discussed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 21 (1973), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: —[3H]Leucine, [3H]glucosamine and [3H]fucose were incorporated in vitro into proteins in frog sciatic ganglia and subsequently transported at a rapid rate along the sciatic nerve towards a ligature, in front of which they accumulated. The synthesis of transported fucose-labelled proteins is closely linked to protein synthesis but is not dependent on RNA synthesis, as judged by effects after incubation for 17 h in the presence of cycloheximide and actinomycin D. Labelled ganglionic as well as transported material were solubilized in sodium dodecyl sulphate and characterized by polyacrylamide gel electrophoresis. The bulk of ganglionic proteins, labelled with any of the precursors used, had molecular weights exceeding 40,000. The radioactivity patterns of leucine- and glucosamine-labelled ganglionic proteins showed similarities with dominant peaks corresponding to molecular weights of about 75,000 and 50,000. The last peak was almost lacking in fucose-labelled ganglionic components. Leucine- and glucosamine labelled-transported proteins exhibited characteristic and similar electrophoretic distributions in contrast to the pattern of fucose-labelled nerve proteins, which was more polydisperse. The most conspicious nerve proteins corresponded to molecular weights of about 75,000 and 18,000. There was a remarkable agreement in the profile of leucine-labelled transported nerve proteins and fucose-labelled ganglionic proteins. In the light of these observations the possibility that glycoproteins constitute a large part of rapidly transported proteins will be discussed.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 23 (1974), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 16 (1969), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— Segments of spinal cords from goldfish or from carp were incubated in vitro in the presence of RNA precursors for varying periods of time. Mauthner nerve fibres were isolated from the fresh unfixed tissue, or, for the separate analyses of axon and myelin sheath, from the fixed spinal cord.The myelinated Mauthner fibre isolated from the incubated spinal cord showed RNA synthesis. A considerable part of the material sedimented at 4S, but part of the nucleic acid was recovered at higher sedimentation values, up to 30S. Newly synthesized RNA was extracted from the isolated myelin sheath as well as from the axon. Isolated myelinated Mauthner fibres were also incubated in vitro with RNA precursors. In this case incorporation occurred exclusively in material sedimenting at 4S or lower. The turnover rate for RNA from the fibre was of a higher order than that of the bulk of RNA from the spinal cord. The findings of RNA synthesis in these tissue components lacking nuclei could possibly be explained as owing to mitochondria.Studies by electron microscopy demonstrated the extent of purity of the isolated components and it was found that contamination was so small as to make it unlikely that the RNA investigated originated in contaminating tissue.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 16 (1969), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— Mauthner nerve fibres isolated from the spinal cord of goldfish were incubated, in the presence of radioactive amino acids for varying periods of time. It was found that the Mauthner fibre synthesizes proteins in the absence of cell nuclei. Amino acid incorporation showed sensitivity to puromycin and to acetoxycycloheximide but resistance to chloramphenicol. Only slight inhibition was caused by actinomycin-D. The contribution of the denuded axon to the total protein synthesis was about 30 per cent per unit length Mauthner fibre. The remaining activity was due to the myelin sheath compartment. Fractionation experiments showed that the incorporation in the sheath was due to components other than the myelin lamellae. The subcellular distribution of newly synthesized proteins in the isolated and incubated Mauthner fibre was compared to that found in the incubated spinal cord. The results strongly suggested the existence in the Mauthner fibre of a primary microsomal, rather than a mitochondrial, protein synthesizing system.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 32 (1979), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The hydrolysis of p-Nitrophenylphosphate has been studied in vitro in a tubulin preparation from bovine brain. The activity at pH 6.8 was 16.4 ± 2.2 nmol/mg protein, h.At least two phosphatases were responsible for this activity. They were found to have pH-optima at 5.1 and 10.4. respectively, and their apparent KM values were 1.23 ± 0.10 mm and 0.17 ± 0.03 mm. respectively. Mg2+ was found to stimulate activity at both pHs while Zn2+ inhibited at pH 5.1 and stimulated activity at pH 10.4.All of the alkaline and part of the acid phosphatase activity were found to be closely associated with microtubules/tubulin. Tubulin purified by phosphocellulose chromatography contained phosphatase activity, and it is suggested that such activity is an intrinsic property of tubulin itself.Phosphatase activity was also found in association with the microtubule-associated proteins that co-purify with tubulin. Two proteins of high molecular weight constituted the major part of the associated material. The results indicate an association of phosphatase activity with the larger of these two proteins.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 33 (1979), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— The effects of two sulfhydryl reagents, PCMBS (p-chloromercuribenzene sulfonic acid) and NEM (N-ethylmaleimide) on microtubule-associated Mg2+ -and Ca2+ -ATPase activity were studied in a MTP (microtubule proteins) preparation and in a MAP (microtubule-associated proteins) fraction. In the MTP preparation at pH 6.8, PCMBS stimulated the Mg2+ -ATPase activity at low concentrations and inhibited at higher, whereas the Ca2+ -ATPdse activity was only inhibited. NEM affected the activity in a similar way. At pH 8.0 PCMBS was only inhibitory. NEM showed stimulatory effects over a broader concentration range.Preincubation in the presence of ATP counteracted the stimulatory effects of both PCMBS and NEM on Mg2+ -ATPase at pH 6.8.In the MAP fraction at pH 6.8 PCMBS and NEM caused similar but less pronounced effects on the Mg2+ -and Ca2+ -ATPase.The results show that brain microtubule-associated ATPase activity is similar to dynein and myosin ATPases with respect to biphasic alteration by sulfhydryl reagents.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 29 (1977), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— Endogenous protein phosphorylation has been studied during in vitro polymerization of microtubules by incubating a purified tubulin preparation at 37°C in the presence of radioactive ATP. At optimal conditions the rate of phosphorylation was found to follow the course of polymerization by a shift to a lower rate at the polymerization plateau.Zn2+ at 0.5 mm was shown to stimulate phosphorylation, mainly of tubulin-associated proteins (mol wt 110,000 and 175,000,) and to a lesser extent of tubulin. The effect occurred at Zn2+-concentrations which induce formation of tubulin sheet polymers, which suggests that the state of aggregation of tubulin is of importance for the phosphorylation. In contrast to Zn2+, Mg2+ only increased phosphorylation of the high molecular weight proteins, and to a lesser degree. The stimulation by Zn2+ or Mg2+ was potentiated by cyclic AMP or cyclic GMP.A low concentration of Zn2+ (5 μm) or cyclic GMP at 10 μm inhibited phosphorylation, possibly by interaction with a co-existing protein phosphatase.
    Type of Medium: Electronic Resource
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