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931.
Shakir Sarhan Patrick Casara Bernd Knödgen Nikolaus Seiler 《Neurochemical research》1991,16(3):285-293
(4S)-4-Amino-5,6-heptadienoic acid ((S)--allenyl-GABA; MDL 72483) is a potent inactivator of brain GABA-T in mice; (ED50 (i.p.)=60 mg·kg–1; ED50 (oral)=70 mg·kg–1). Its anticonvulsant effects against 3-mercaptopropionic acid (MPA)-induced seizures in mice is related to the elevation of whole brain GABA concentrations: The mentioned doses of MDL 72483 which cause a decrease of GABA-T activity by 50%, produce within 5 h after dosing an increase of GABA concentration by about 3 mol·g–1, and protect 50% of the mice against seizures in this model of presynaptic GABA deficit. When given orally MDL 72483 is about five times more potent than vigabatrin ((4R/S)-4-amino-5-hexenoic acid) a known antiepileptic GABA-T inhibitor. Complete protection was achieved with a dose of 150 mg·kg–1. Similar to vigabatrin, MDL 72483 does not protect significantly against metrazol-induced convulsions. However, at a dose of 300 mg·kg–1, the time elapsing between metrazol administration and onset of convulsions was prolonged by a factor of 3.4. Oral administration of MDL 72483 for up to 19 days at a daily dose of 91–96 mg·kg–1 did not produce any obvious behavioral changes in mice, nor was the ED50 of the drug in MPA-seizure tests significantly altered by the pretreatment. These observations indicate that MDL 72483 is a promising drug for the treatment of certain epilepsies.Special issue dedicated to Dr. Eugene Roberts. 相似文献
932.
933.
Bernd Krüger Ortwin Meyer Matthias Nagel Jan R. Andreesen Michael Meincke Eberhard Bock Sendor Blümle Walter G. Zumft 《FEMS microbiology letters》1987,48(1-2):225-227
Abstract Bactopterin was resolved in the eubacterial molybdoenzymes nicotinic acid dehydrogenase from Bacillus niacini , nitrite oxidoreductase from Nitrobacter hamburgensis and respiratory nitrate reductase from Pseudomonas stutzeri . These findings lend support to the proposal that bactopterin is a common cofactor of eubacterial molybdoenzymes. 相似文献
934.
Michael Bachmann August Bernd Heinz C. Schröder Rudolf K. Zahn Werner E.G. Müller 《生物化学与生物物理学报:生物膜》1984,773(2):308-316
The activities of nuclear envelope-associated protein phosphokinase and protein phosphatase were determined in nuclear ghosts from liver and oviduct of quails. The protein kinase was found to be inhibited by poly(A) by 75%. During the kinase reaction proteins with molecular weights of 106 000 and 64 000 were phosphorylated. The phosphoprotein phosphatase from liver was stimulated to 190% by poly(A), whereas only a slight enhancing effect by this polymer was determined with the oviduct enzyme (to 125%). Comparative determinations of the nuclear ghost-associated enzyme activities revealed the following values (in nmol Pi/min per 108 ghosts); oviduct: phosphokinase, 0.015; phosphatase, 0.004 and nucleoside triphosphatase, 39.4; and liver: phosphokinase, 0.044; phosphatase, 0.012 and nucleoside triphosphatase, 11.7. These data indicate that phosphorylation/dephosphorylation proceeds independently of the nucleoside triphosphatase cycle. This assumption is supported by analytical results revealing that no marked dephosphorylation occurs after poly(A) binding to the nuclear envelope. Moreover, stoichiometrical data showed a nearly 1:1 molar ratio between ATP-binding and phosphorylation of nuclear envelope protein. From these findings a new model for the nucleoside triphosphatase-mediated poly(A)(+)mRNA efflux from nuclei is deducted, proposing phosphokinase and phosphatase only to modulate the affinity of the ‘carrier structure’ for poly(A) (+)mRNA, but not to constitute the nucleoside triphosphatase. 相似文献
935.
Otto Baumann Bernd Walz 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1989,165(5):627-636
Summary The photoreceptor cells in the honeybee drone contain an elaborate Ca2+-sequestering endoplasmic reticulum (ER). We measured Ca-oxalate formation within the ER of permeabilized retinal slices with a microphotometer and studied the kinetics of Ca2+-uptake into the ER and the properties of Ins(1,4,5)P3-induced Ca2+-release.The ATP-dependent Ca2+-uptake mechanism has a high affinity for Ca2+: Uptake rate was half maximal at Ca2+
free 0.6 M.Addition of Ins(1,4,5)P3 caused a persistent depression of Ca-oxalate formation due to Ca2+ -release from the ER. The Ins(1,4,5)P3-dependent Ca2+-release mechanism has a high affinity (half maximal rate with 0.2 M Ins(1,4,5)P3) and a high specificity for Ins(1,4,5)P3: Ins(2,4,5)P3 was 6 times, Ins(1,3,4,5)P4 was 15 times less potent in inducing Ca2+-release. 3 M Ins(1,4)P2 had no detectable effect. The sensitivity for Ins(1,4,5)P3 was maximal between 280 nM and 1.6 M Ca2+
free and decreased at higher and lower Ca2+-concentrations.Our data show that the ER in invertebrate photoreceptor cells is an effective Ca2+ -sink and an Ins(1,4,5)P3-sensitive Ca2+-source. We support the idea (Payne et al. 1988) that the ER-network close to the photoreceptive membrane, the submicrovillar cisternae (SMC), are the light- and Ins(1,4,5)P3-sensitive Ca2+-stores.Abbreviations
ER
endoplasmic reticulum
-
Ins(1,4,5)P
3
D-inositol 1,4,5-trisphosphate
-
Ins(1,3,4)P
3
D-inositol 1,3,4-trisphosphate
-
Ins(2,4,5)P
3
D-inositol 2,4,5-trisphosphate
-
Ins(1,4)P
2
D-inositol 1,4-bisphosphate
-
Ins(1,3,4,5)P
4
D-inositol 1,3,4,5-tetrakisphosphate
-
SMC
submicrovillar cisternae
-
[Ca
2+]i
intracellular free Ca2+-concentration 相似文献
936.
Evidence for oxidative thiolytic cleavage of acetoin in Pelobacter carbinolicus analogous to aerobic oxidative decarboxylation of pyruvate 总被引:3,自引:0,他引:3
Fred Bernd Oppermann Alexander Steinbüchel Hans G. Schlegel 《FEMS microbiology letters》1989,60(1):113-118
Dihydrolipoamide dehydrogenase and dihydrolipoamide acetyltransferase were formed when Pelobacter carbinolicus strain GraBd1 was grown on acetoin. The specific activities of these enzymes amounted to 0.50 and 28.7 U/mg protein, respectively. The crude extract catalyzed the CoASH- and NAD+-dependent formation of acetyl-CoA from acetoin and methylacetoin. From ethylene glycol-grown cells these activities were absent. Crude extracts also exhibited acetoin: methyl viologen and acetoin: metronidazole oxidoreductase activity. As shown by reconstitution experiments methylviologen reduction was dependent on the presence of a light-brownish protein (Mr 220,000 +/- 10,000); metronidazole reduction was in addition dependent on the presence of a dark-brownish protein (Mr 4,900 +/- 800), which is probably a ferredoxin. However, both components were synthesized constitutively. We discussed a model for oxidative-thiolytic cleavage of acetoin which is analogous to the reaction of the pyruvate dehydrogenase enzyme complex rather than to pyruvate: ferredoxin oxidoreductase. 相似文献
937.
Bernd Heinrich 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1984,154(2):175-180
Summary
D. maculata, the white-faced hornet, stabilized (regulated) thoracic temperature (T
Th) over wide ranges of ambient temperature (T
a), whileV. vulgaris, the common yellowjacket, regulatedT
Th poorly. The hornets also maintained a higherT
Th than the wasps, sometimes heating 38°C aboveT
a. Attacking individuals of both species had higherT
Th than those either leaving or returning to the nest from foraging. The hornets, who are primarily hunters of live prey, showed peak activity near dawn, and they were as active atT
a=2°C as at 20°C. Being able to regulate theirT
Th and fly at the lowT
a should enhance their ability to capture small insects that are usually torpid at theseT
a. The yellowjacket wasps, on the other hand, who are scavengers as well as hunters, did not leave the nest at 2°C; their activity decreased greatly with decreasingT
a. Differences in the foraging technique of the two vespids may be related to their different abilities to thermoregulate. 相似文献
938.
A new sensitive method for qualitative and quantitative assay of neomycin phosphotransferase in crude cell extracts 总被引:57,自引:0,他引:57
A general method is described for the detection and quantification of low amounts of neomycin phosphotransferase in crude cell extracts. The assay is based on the electrophoretic separation of the enzyme from other interfering proteins and detection of its enzymatic activity by in situ phosphorylation of the antibiotic kanamycin. Both kanamycin and [γ32P]ATP acting as substrates are embedded in an agarose gel placed on the polyacrylamide gel containing the separated proteins. After the enzymatic reaction, the phosphorylated kanamycin is transferred to P81 phosphocellulose ion exchange paper and the radiolabeled kanamycin is visualised by autoradiography. With this method 1 ng of active enzyme can easily be detected. Both prokaryotic and eukaryotic cell extracts can be examined, and changes in the size of enzymatically active proteins can be determined. 相似文献
939.
Platycnemis pennipes deposits eggs into plant tissue at or just below the water surface. On a number of different plant species egg deposition rate was found to be similar, while oviposition duration varied. Eggs were not always to be found in the substrate after a female had probed the substrate with her ovipositor. Actual oviposition took place only during longer stays. 相似文献
940.
Bernd Friesenbichler Lisa M. Stirling Peter Federolf Benno M. Nigg 《Journal of biomechanics》2011,44(1):116-120
The impact force in heel–toe running initiates vibrations of soft-tissue compartments of the leg that are heavily dampened by muscle activity. This study investigated if the damping and frequency of these soft-tissue vibrations are affected by fatigue, which was categorized by the time into an exhaustive exercise. The hypotheses were tested that (H1) the vibration intensity of the triceps surae increases with increasing fatigue and (H2) the vibration frequency of the triceps surae decreases with increasing fatigue. Tissue vibrations of the triceps surae were measured with tri-axial accelerometers in 10 subjects during a run towards exhaustion. The frequency content was quantified with power spectra and wavelet analysis. Maxima of local vibration intensities were compared between the non-fatigued and fatigued states of all subjects. In axial (i.e. parallel to the tibia) and medio-lateral direction, most local maxima increased with fatigue (supporting the first hypothesis). In anterior–posterior direction no systematic changes were found. Vibration frequency was minimally affected by fatigue and frequency changes did not occur systematically, which requires the rejection of the second hypothesis. Relative to heel-strike, the maximum vibration intensity occurred significantly later in the fatigued condition in all three directions. With fatigue, the soft tissue of the triceps surae oscillated for an extended duration at increased vibration magnitudes, possibly due to the effects of fatigue on type II muscle fibers. Thus, the protective mechanism of muscle tuning seems to be reduced in a fatigued muscle and the risk of potential harm to the tissue may increase. 相似文献